SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 4 KEY PRODUCT FEATURES GENERAL DESCRIPTION The SX8650 is an ultra low power 4-wire resistive touchscreen controller optimized for portable equipment where power and board-space are at a premium. It incorporates a highly accurate 12-bit ADC for data conversion and operates from a single 1.65 to 3.7V supply voltage. The SX8650 features a built-in preprocessing algorithm for data measurements, which greatly reduces the host processing overhead and bus activity. This complete touchscreen solution includes four user-selectable operation modes which offer programmability on different configurations such as conversion rate and settling time, thus enable optimization in throughput and power consumption for a wide range of touch sensing applications. The touch screen inputs have been specially designed to provide robust on-chip ESD protection of up to 15kV in both HBM and Contact Discharge, and eliminates the need for external protection devices. The SX8650 supports the Fast-mode IC (400kbit/s) serial bus data protocol and includes 2 user-selectable slave addresses. A custom I2C address is possible on request. The SX8650 is offered in two tiny packages: 3.0 mm x 3.0 mm DFN and a 1.5 mm x 2.0 mm wafer-level chip-scale package (WLCSP). APPLICATIONS Extremely Low Power Consumption: 23uA@1.8V 8kSPS Superior On-chip ESD Protection 15kV HBM (X+,X-,Y+,Y-) 2kV CDM 25kV Air Gap Discharge 15kV Contact Discharge 300V MM Single 1.65V to 3.7V Supply/Reference Integrated Preprocessing Block to Reduce Host Loading and Bus Activity Four User Programmable Operation Modes provides Flexibility to address Different Application Needs Manual, Automatic, Pen Detect, Pen Trigger High Precision 12-bit Resolution Low Noise Ratiometric Conversion Selectable Polling or Interrupt Modes Touch Pressure Measurement 400kHz Fast-Mode IC Interface Hardware Reset & IC Software Reset -40C to 85C Operation 12-LD (3.0 mm x 3.0 mm) DFN Package 12-Ball (1.5 mm x 2.0 mm) WLCSP Package Pin-compatible with SX8651 Pb-Free, Halogen Free, RoHS/WEEE compliant product Windows CE 6.0, Linux Driver Support Available ORDERING INFORMATION Portable Equipment Mobile Communication Devices Part Number Cell phone, PDA, MP3, GPS, DSC Touch Screen Monitors Block Diagram Package SX8650ICSTRT1 12 - Ball WLCSP (1.5 mm x 2.0 mm) SX8650IWLTRT1 12 - Lead DFN (3.0 mm x 3.0 mm) 1. 3000 Units / reel SX8650 VDD AUX Control A0 X+ NRST POR OSC I2C Y+ XYGND Revision V2.19/October 2010 (c)2010 Semtech Corp. Touch Screen Interface Vref SCL HOST ref+ in ADC out ref- Page 1 SDA Digital Filter NIRQ www.semtech.com SX8650 ADVANCED COMMUNICATIONS & SENSING DATASHEET Table of contents Section 1. 2. 3. General Description ................................................................................................................................................. 4 1.1. DFN Pinout Diagram and Marking Information (Top View).............................................................................. 4 1.2. WLCSP Pinout Diagram and Marking Information (Top View) ........................................................................ 4 1.3. Pin Description................................................................................................................................................. 5 1.4. Simplified Block Diagram ................................................................................................................................. 5 Electrical Characteristics ......................................................................................................................................... 6 2.1. Recommended Operating Conditions.............................................................................................................. 6 2.2. Thermal Characteristics ................................................................................................................................... 6 2.3. Electrical Specifications ................................................................................................................................... 7 2.4. Host Interface Specifications ........................................................................................................................... 9 2.5. Host Interface Timing Waveforms.................................................................................................................. 10 2.6. Typical Operating Characteristics .................................................................................................................. 11 Functional Description ........................................................................................................................................... 13 3.1. General Introduction ..................................................................................................................................... 13 3.2. Channel Pins.................................................................................................................................................. 13 3.2.1. X+, X-, Y+. Y- .......................................................................................................................................... 13 3.2.2. AUX ......................................................................................................................................................... 13 3.3. 5. Host Interface and Control Pins ..................................................................................................................... 14 3.3.1. NIRQ ....................................................................................................................................................... 14 3.3.2. SCL ......................................................................................................................................................... 14 3.3.3. SDA ......................................................................................................................................................... 14 3.3.4. A0 ............................................................................................................................................................ 15 3.3.5. NRST ...................................................................................................................................................... 15 3.4. 4. Page Power Management Pins............................................................................................................................... 15 3.4.1. VDD......................................................................................................................................................... 15 3.4.2. GND ........................................................................................................................................................ 15 Detailed Description............................................................................................................................................... 16 4.1. Touch Screen Operation................................................................................................................................ 16 4.2. Coordinates Measurement............................................................................................................................. 17 4.3. Pressure Measurement.................................................................................................................................. 17 4.4. Pen Detection ................................................................................................................................................ 18 Data Processing .................................................................................................................................................... 19 5.1. Host Interface and Control ............................................................................................................................. 19 5.1.1. I2C Address ............................................................................................................................................ 19 5.1.2. I2C Write Registers ................................................................................................................................. 20 5.1.3. I2C Read Registers ................................................................................................................................. 21 5.1.4. I2C Host Commands ............................................................................................................................... 21 5.1.5. I2C Read Channels ................................................................................................................................ 22 5.1.6. Data Channel Format ............................................................................................................................. 23 Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 2 www.semtech.com SX8650 ADVANCED COMMUNICATIONS & SENSING DATASHEET Table of contents Section Page 5.1.7. 6. 7. 8. Invalid Qualified Data .............................................................................................................................. 23 5.2. I2C Register Map .......................................................................................................................................... 23 5.3. Host Control Writing....................................................................................................................................... 24 5.4. Host Commands ............................................................................................................................................ 26 5.5. Power-Up ....................................................................................................................................................... 27 5.6. Reset.............................................................................................................................................................. 27 Modes of Operation .............................................................................................................................................. 27 6.1. Manual Mode ................................................................................................................................................. 28 6.2. Automatic mode ............................................................................................................................................. 29 6.3. PENDET Mode .............................................................................................................................................. 30 6.4. PENTRIG Mode ............................................................................................................................................. 30 Application Information .......................................................................................................................................... 31 7.1. Acquisition Setup ........................................................................................................................................... 31 7.2. Channel Selection.......................................................................................................................................... 31 7.3. Noise Reduction............................................................................................................................................. 31 7.3.1. POWDLY................................................................................................................................................. 31 7.3.2. SETDLY .................................................................................................................................................. 32 7.3.3. AUX Input ................................................................................................................................................ 32 7.4. Interrupt Generation....................................................................................................................................... 32 7.5. Coordinate Throughput Rate ......................................................................................................................... 32 7.5.1. I2C Communication Time........................................................................................................................ 33 7.5.2. Conversion Time ..................................................................................................................................... 33 7.5.3. AUTO MODE .......................................................................................................................................... 33 7.6. ESD event...................................................................................................................................................... 33 7.7. Application Schematic.................................................................................................................................... 34 7.8. Application Examples..................................................................................................................................... 34 7.8.1. Soft Keyboard ......................................................................................................................................... 34 7.8.2. Slider Controls......................................................................................................................................... 34 7.8.3. Game ...................................................................................................................................................... 35 7.8.4. Handwriting Application........................................................................................................................... 35 Packaging Information ........................................................................................................................................... 36 8.1. DFN Package................................................................................................................................................. 36 8.2. WLCSP Package ........................................................................................................................................... 38 Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 3 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 1. General Description 1.1. DFN Pinout Diagram and Marking Information (Top View) VDD 1 X+ 2 Y+ 3 SX8650 TOP VIEW 12 AUX 11 A0 10 NRST 8650 YYWW 13 X- 4 9 SCL Y- 5 8 SDA GND 6 7 NIRQ XXXX PIN 1 IDENTIFIER Figure 1. SX8650SX8650 DFN Top View, Pad on Bottom Side YYWW : date code XXXXX: Lot Number 1.2. WLCSP Pinout Diagram and Marking Information (Top View) SX8650 TOP VIEW solder bumps on bottom side X+ Y+ X- Y- VDD A0 NRST GND AUX NIRQ SDA SCL C D 3 8650 Eyww 2 1 A B BALL A1 IDENTIFIER Figure 2. SX8650 WLCSP Top View, Solder Bumps on Bottom Side YYWW : date code XXXXX: Lot Number Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 4 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 1.3. Pin Description Pin Number # Name Type Description DFN WLCSP 1 A2 VDD Power Input power supply connect to a 0.1uF capacitor to GND 2 A3 X+ Analog X+ channel input 3 B3 Y+ Analog Y+ channel input 4 C3 X- Analog X- channel input 5 D3 Y- Analog Y- channel input 6 D2 GND Ground Ground 7 B1 NIRQ Digital Output / Open Drain Output Interrupt output, active low. Need external pull-up resistor 8 C1 SDA Digital Input / Open Drain Output I2C data input/output 9 D1 SCL Digital Input / Open Drain Output I2C clock, input/output 10 C2 NRST Digital Input / Output Reset Input, active low. Need external 50k pull-up resistor 11 B2 A0 Digital Input I2C slave address selection input 12 A1 AUX Digital Input/Analog Input Analog auxiliary input or conversion synchronization 13 GND Ground Die attach paddle, connect to Ground Table 1 Pin description 1.4. Simplified Block Diagram The SX8650 simplified block diagram is shown in Figure 3. SX8650 VDD AUX Control X+ A0 Y+ NRST POR X- YGND OSC I2C SCL Touch Screen Interface Vref ref+ in ADC out ref- SDA Digital Filter NIRQ Figure 3. Simplified block diagram of the SX8650 Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 5 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 2. Electrical Characteristics Stresses above the values listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these, or any other conditions beyond the "Recommended Operating Conditions", is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Parameter Symbol Min. Max. Unit Supply Voltage VDDABS -0.5 3.9 V Input voltage (non-supply pins) VIN -0.5 3.9 V Input current (non-supply pins) IIN 10 mA Operating Junction Temperature TJCT 125 C Reflow temperature TRE 260 C Storage temperature TSTOR 150 C High ESD pins: X+, X-,Y+,YESD HBM (Human Body Model) All pins except high ESD pins: AUX,A0,NRST,NIRQ,SDA,SCL ESD (Contact Discharge) High ESD pins: X+, X-,Y+,Y- Latchup -50 15(i) kV 8(ii) kV ESDHBM2 2 kV ESDCD 15 kV ILU 100(iii) mA ESDHBM1 Table 2. Absolute Maximum Ratings (i) (ii) (iii) Tested to TLP (10A) Tested to JEDEC standard JESD22-A114 Tested to JEDEC standard JESD78 2.1. Recommended Operating Conditions Parameter Supply Voltage Ambient Temperature Range Symbol Min. Max Unit VDD 1.65V 3.7 V TA -40 85 C Symbol Min. Max Unit 2.2. Thermal Characteristics Parameter Thermal Resistance with DFN package - Junction to Ambient (i) JA 39 C/W Thermal Resistance with WLCSP package - Junction to Ambient (i) JA 65 C/W (iii) JA is calculated from a package in still air, mounted to 3" x 4.5", 4 layer FR4 PCB with thermal vias under exposed pad (if applicable) per JESD51 standards. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 6 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 2.3. Electrical Specifications Parameter Symbol Conditions Min. Typ Max Unit Current consumption Manual Ipwd Manual (converter stopped, pen detection off, I2C listening, OSC stopped) 0.4 0.75 uA Pen Detect Ipndt Pen detect mode (converter stopped, pen detection activated, device will generate interrupt upon detection, I2C listening, OSC stopped). 0.4 0.75 uA Pen Trigger Ipntr Pen trigger mode (converter stopped, pen detection activated, device will start conversion upon pen detection. I2C listening, OSC stopped 0.4 0.75 uA Automatic Iwt Automatic (converter stopped, pen detection off, I2C listening, OSC and timer on, device is waiting for timer expiry) 1.5 Operation @8kSPS, VDD=1.8V Iopl X,Y Conv. RATE=4kSPS, Nfilt=1 PowDly=0.5us, SetDly=0.5us 23 50 uA Operation @42kSPS, VDD=3.3V Ioph X,Y Conv. RATE=3kSPS, Nfilt=7 PowDly=0.5us, SetDly=0.5us 105 140 uA uA Digital I/O High-level input voltage 1 VIH 0.7VDD VDD+0.5 V Low-level input voltage VIL VSS-0.3 0.3VDD V SDA / SCL Hysteresis of Schmitt Vhys trigger inputs VDD > 2 V VDD < 2 V Low-level output voltage Input leakage current VOL LI 0.05VDD 0.1VDD IOL=3mA, VDD>2V IOL=3mA, VDD<2V V 0 0 0.4 0.2VDD CMOS input V 1 uA VDD V AUX Input voltage range VIAUX Input capacitance CX+,CX-,CY+, CY- 50 pF CAUX 5 pF Revision V2.19/October 2010 (c)2010 Semtech Corp. 0 Page 7 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET Symbol Parameter Input leakage current Conditions IIAUX Min. Typ -1 Max Unit 1 uA 1 ms Startup Power-up time (Delay tPOR Time between rising edge VDD and rising NIRQ Reset tNRST 50 ns Resolution Ares 12 bits Offset Aoff Gain error Age Differential nonlinearity Integral nonlinearity Reset low time ADC 1 LSB 0.5 LSB Adnl 1 LSB Ainl 1.5 LSB 5 Ohm At full scale Resistors X+, X-, Y+, Y- resistance Rchn Touch Pad Biasing Resistance Pen detect resistance RPNDT_00 RPNDT = 0 100 kOhm RPNDT_01 RPNDT = 1 200 kOhm RPNDT_10 RPNDT = 2 50 kOhm RPNDT_11 RPNDT = 3 25 kOhm 0.1 uF External components Capacitor between VDD, GND recommendations Cvdd Type 0402, tolerance +/-50% 1. SCL, SDA, NRST and NIRQ can be pulled up to a potential higher than the chip VDD but must not exceed the maximun voltage of 3.7V. All values are valid within the recommended operating conditions unless otherwise specified. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 8 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 2.4. Host Interface Specifications Parameter Symbol Condition Min Typ Max Unit 400 kHz I2C TIMING SPECIFICATIONS (i) SCL clock frequency fSCL 0 SCL low period tLOW 1.3 us SCL high period tHIGH 0.6 us Data setup time tSU;DAT 100 ns Data hold time tHD;DAT 0 ns Repeated start setup time tSU;STA 0.6 us Start condition hold time tHD;STA 0.6 us Stop condition setup time tSU;STO 0.6 us Bus free time between stop and start tBUF 1.3 us Data valid time tVD;DAT 0.9 us Data valid ack time tVD;ACK 0.9 us Pulse width of spikes that must be suppressed by the input filter tSP 50 ns Capacitive Load on each bus line SCL, SDA Cb 400 pF I2C BUS SPECIFICATIONS Table 3 Host Interface Specifications Notes: (i) All timing specifications refer to voltage levels (VIL, VIH, VOL) defined in Table 3 unless otherwise mentioned. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 9 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 2.5. Host Interface Timing Waveforms 70% 30% SDA 70% SCL tSU;STA tHD;STA tSU;STO tBUF Figure 4. I2C Start and Stop timing SDA 70% 30% SCL 70% 30% tLOW tHIGH tHD;DAT tSU;DAT tSP Figure 5. I2C Data timing Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 10 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 2.6. Typical Operating Characteristics At Ta= -40C to +85C, VDD=1.7V to 3.7V, PowDly=0.5 us, SetDly=0.5us, Filt=1, Resistive touch screen sensor current not taking in account, unless otherwise noted. SUPPLY CURRENT in MANUAL MODE vs TEMPERATURE CURRENT IN PEN TRIGGER MODE 500 700 V DD=3.3V Manual Mode Supply Current (nA) TOUCH SENSOR NOT ACTIVATED Supply Current (nA) 400 300 200 100 600 VDD=1.85V 500 400 300 200 100 0 0 1.5 2 2.5 3 -40 3.5 -20 0 40 60 80 100 SUPPLY CURRENT VS CONVERSION RATE VDD=1.8V - X,Y, Z1, Z2 CONVERSION SUPPLY CURRENT VS CONVERSION RATE VDD=1.8V - X,Y CONVERSION 130 100 90 120 Filt=7 Supply Current (uA) Filt=5 70 60 50 Filt=3 40 30 Filt=5 110 100 80 Supply Current (uA) 20 Temperature (C) V DD (V) Filt=1 90 Filt=3 80 70 60 50 Filt=1 40 20 30 20 10 10 0 Filt=7 0 0 1 2 3 4 5 0 Conversion Rate (kCPS) 1 2 3 4 5 Conversion Rate (kCPS) SUPPLY CURRENT vs SAMPLE RATE 500 TOUCH SENSOR X+ to X- =1000 Ohm Y+ to Y- =1000 Ohm 400 V DD=3.3V Supply Current (uA) V DD=2.5V 300 V DD=1.65V 200 100 0 0 1 2 3 4 5 Sample Rate (kCPS) Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 11 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET Typical Operating Characteristics (continued) At Ta= -40C to +85C, VDD=1.7V to 3.7V, PowDly=0.5 us, SetDly=0.5us, Filt=1, Resistive touch screen sensor current not taking in account, unless otherwise noted. CHANGE IN ADC OFFSET vs. TEMPERATURE 2 2 1 1 Delta from +25C (LSB) Delta from +25C (LSB) CHANGE IN ADC GAIN vs. TEMPERATURE 0 -1 -2 -40 -20 0 20 40 60 80 0 -1 -2 -40 100 Temperature (C) -20 0 20 40 60 80 100 Temperature (C) ADC INL @ VDD=3.3V 1 0.75 Error (LSB) 0.5 0.25 0 -0.25 -0.5 -0.75 -1 0 0.5 1 1.5 2 2.5 3 VX+(V) Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 12 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 3. Functional Description 3.1. General Introduction This section provides an overview of the SX8650 architecture, device pinout and a typical application. The SX8650 is designed for 4-wire resistive touch screen applications (Figure 6).The touch screen or touch panel is the resistive sensor and can be activated by either a finger or stylus. The touch screen coordinates and touch pressure are converted into I2C format by the SX8650 for transfer to the host. SX8650 VDD AUX Control VDD_HOST A0 NRST X+ POR OSC I2C Y+ XY- SCL Touch Screen Interface GND Vref HOST SDA ref+ in ADC out ref- Digital Filter NIRQ Figure 6. SX8650 with screen 3.2. Channel Pins 3.2.1. X+, X-, Y+. YThe SX8650's channel pins (X+, X-, Y+, Y-) directly connect to standard touch screen X and Y resistive layers. The SX8650 separately biases each of these layers and converts the resistive values into (X,Y) coordinates. VDD X+ XY+ Y- Rchn Touch Screen Interface The channel pins are protected to VDD and GROUND. Figure 7 shows the simplified diagram of the X+, X-, Y+, Y- pins. Figure 7. Simplified diagram of X+, X-, Y+, Y- pins 3.2.2. AUX The SX8650 interface includes an AUX pin that serves two functions: an ADC input; and a start of conversion trigger. When used as an ADC, the single ended input range is from GND to VDD, referred to GND. When the AUX input is configured to start conversions, the AUX input can be further configured as a rising and / or falling edge trigger. VDD ADC AUX The AUX is protected to VDD and GROUND. Control Figure 8 shows a simplified diagram of the AUX pin. Figure 8. Simplified diagram of AUX Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 13 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 3.3. Host Interface and Control Pins The SX8650 host and control interface consists of: NIRQ, I2C pins SCL and SDA, A0, and NRST. 3.3.1. NIRQ The NIRQ pin is an active low, open drain output to facilitate interfacing to different supply voltages and thus requires an external pull-up resistor (110 kOhm). The NIRQ pin does not have protection to VDD. HOST VDD IRQ Control NIRQ The NIRQ function is designed to provide an interrupt to the host processor. Interrupts may occur when a pen is detected, or when channel data is available. Figure 9 shows a simplified diagram of the NIRQ pin. Figure 9. Simplified diagram of NIRQ 3.3.2. SCL The SCL pin is a high-impedance input and opendrain output pin. The SCL pin does not have protection to VDD to conform to I2C slave specifications. An external pull-up resistor (1-10 kOhm) is required. HOST VDD Figure 10 shows the simplified diagram of the SCL pin. SCL IN SCL I2C OUT Figure 10. Simplified diagram of SCL 3.3.3. SDA SDA is an I/O pin. It can be used as an open-drain output (with external pull-up resistor) or as an input. An external pull-up resistor (1-10 kOhm) is required. HOST VDD SDA IN SDA I2C OUT The SDA I/O pin does not have protection to VDD to conform to I2C slave specifications. Figure 11 shows a simplified diagram of the SDA pin. Figure 11. Simplified diagram of SDA Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 14 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 3.3.4. A0 The A0 pin is connected to the I2C address select control circuitry and is used to modify the device I2C address. A0 The A0 pin is protected to GROUND. I2C Figure 12 shows a simplified diagram of the A0 pin. Figure 12. Simplified diagram of A0 3.3.5. NRST The NRST pin is an active low input that provides a hardware reset of the SX8650's control circuitry. HOST VDD The NRST pin is protected GROUND to enable interfacing with devices at a different supply voltages. Control NRST Figure 13 shows a simplified diagram of the NRST pin. Figure 13. Simplified diagram of NRST 3.4. Power Management Pins The SX8650's power management input consists of the following Power and Ground pins. 3.4.1. VDD VDD The VDD is a power pin and is the power supply for the SX8650. The VDD has ESD protection to GROUND. Figure 14 shows a simplified diagram of the VDD pin. VDD Figure 14. Simplified diagram of VDD 3.4.2. GND VDD The SX8650 has one power management ground pin, GND. (The die attach paddle on DFN is also connected to GND.) The GND has ESD protection to VDD. Figure 15 shows a simplified diagram of the GND pin. GND Figure 15. Simplified diagram of GND Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 15 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 4. Detailed Description 4.1. Touch Screen Operation A resistive touch screen consists of two (resistive) conductive sheets separated by an insulator when not pressed. Each sheet is connected through 2 electrodes at the border of the sheet (Figure 16). When a pressure is applied on the top sheet, a connection with the lower sheet is established. Figure 17 shows how the Y coordinate can be measured. The electrode plates are connected through terminals X+, X- and Y+, Y- to an analog to digital converter (ADC) and a reference voltage. The resistance between the terminals X+ and X- is defined by Rxtot. Rxtot will be split in 2 resistors, R1 and R2, in case the screen is touched. The resistance between the terminals Y+ and Y- is represented by R3 and R4. The connection between the top and bottom sheet is represented by the touch resistance (RT). Y+ top conductive sheet electrodes Y- electrodes X+ X- bottom conductive sheet Figure 16. 4-wire Touch Screen Y+ R3 X- + Vref - RT R2 R1 X+ + - ADC Ypos R4 YFigure 17. Touch Screen Operation ordinate measurement (Y) Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 16 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 4.2. Coordinates Measurement The top resistive sheet (Y) is biased with a voltage source. Resistors R3 and R4 determine a voltage divider proportional to the Y position of the contact point. Since the converter has a high input impedance, no current flows through R1 so that the voltage X+ at the converter input is given by the voltage divider created by R3 and R4. The X coordinate is measured in a similar fashion with the bottom resistive sheet (X) biased to create a voltage divider by R1 and R2, while the voltage on the top sheet is measured through R3. Figure 18 shows the coordinates measurement setup. The resistance RT is the resistance obtained when a pressure is applied on the screen. RT is created by the contact area of the X and Y resistive sheet and varies with the applied pressure. Ypos X+ Y+ R1 X+ R3 RT R2 R1 + Vref - + Vref - R4 X- Y+ Xpos R3 RT R2 Y- R4 X- Y- Figure 18. Ordinate (Y) and abscissa (X) coordinates measurement setup The X and Y position are found by: Xpos R2 = 4095 -------------------R1 + R2 R4 Ypos = 4095 -------------------R3 + R4 4.3. Pressure Measurement The pressure measurement consists of two additional setups: z1 and z2 (see Figure 19). X+ Y+ R1 + Vref - z1 X+ R1 R3 + Vref - RT R2 Y+ R3 RT R2 R4 R4 z2 X- Y- X- Y- Figure 19. z1 and z2 pressure measurement setup The corresponding equations for the pressure: Revision V2.19/October 2010 (c)2010 Semtech Corp. R4 z1 = 4095 --------------------------------R1 + R4 + R T Page 17 R4 + Rt z2 = 4095 --------------------------------R1 + R4 + R T www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET The X and Y total sheet resistance (Rxtot, Rytot) are known from the touch screen supplier. Rxtot = R1 + R2 Rytot = R3 + R4 R4 is proportional to the Y coordinate. The R4 value is given by the total Y plate resistance multiplied by the fraction of the Y Ypos R4 = Rytot -----------position over the full coordinate range. 4095 z2 R T = R4 ----- - 1 By re-arranging z1 and z2 one obtains z1 Ypos R T = Rytot ------------ 4095 Which results in: z2 ----- - 1 z1 The touch resistance calculation above requires three channel measurements (Ypos, z2 and z1) and one specification data (Rytot).An alternative calculation method is using Xpos, Ypos, one z channel and both Rxtot and Rytot shown in the next calculations R1 is inverse proportional to the X coordinate. Xpos R1 = Rxtot 1 - ------------4095 Substituting R1 and R4 into z1 and rearranging terms Rytot Y pos 4095 Xpos R T = ------------------------------- ------------ - 1 - Rxtot 1 - ------------gives: 4095 z1 4095 4.4. Pen Detection RPNDT Y+ + Vref - Y- X+ R3 RT R1 R4 R2 X- The pen detection circuitry is used both to detect a user action and generate an interrupt or start an acquisition in PENDET and PENTRG mode respectively. Doing a pen detection prior to conversion avoids feeding the host with dummy data and saves power. If the touchscreen is powered between X+ and Y- through a resistor RPNDT, no current will flow so long as pressure is not applied to the surface (see Figure 20). When some pressure is applied, a current path is created and brings X+ to the level defined by the resistive divider determined by RPNDT and the sum of R1, RT and R4. The level is detected by a comparator. Figure 20. Pen detection RPNDT should be set to the greatest value 200 kOhm for optimal detection (see Table 6). Increasing PowDly settings can also improve the detection on panel with high resistance. The pen detection will set the PENIRQ bit of the RegStat register. In PENDET mode, the pen detection will set NIRQ low. The PENIRQ bit will be cleared and the NIRQ will be de-asserted as soon as the host reads the status register. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 18 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 5. Data Processing NFILT The SX8650 offers 4 types of data processing which allows the user to make trade-offs between data throughput, power consumption and noise rejection. Preprocessing ADC cn,cn-1,cn-2,... Sort: .>.>.>.>. sn The parameter FILT is used to select the filter order Nfilt . The noise rejection will be improved with a high order to the detriment of the power consumption. The K coefficient in Table 4 is a filter constant. Its value is K=4079/4095. I2C N-1 1 sn = cn-i N i=0 Figure 21. Filter structure . FILT Nfilt 0 1 Processing sn = cn No average. 1 3 2 5 1--- 4079 -----------n = 3 4095 ( c n + c n - 1 + c n - 2 ) 3 ADC samples are averaged 1 4079 s n = --- ------------ ( c n + c n - 1 + c n - 2 + c n - 3 + c n - 4 ) 5 4095 5 ADC samples are averaged 3 7 c max1 c max2 c a c b c c c min1 c min2 1 4079 --- -----------n = 3 4095 ( c a + c b + c c ) 7 ADC samples are sorted and the 3 center samples are averaged Table 4. Filter order 5.1. Host Interface and Control The host interface consists of I2C (SCL and SDA) and the NIRQ, A0, NRST signals. The I2C implemented on the SX8650 is compliant with: Standard Mode (100 kbit/s) & Fast Mode (400 kbit/s) Slave mode 7 bit slave address 5.1.1. I2C Address Pin A0 defines the LSB of the I2C address. It is shown on Figure 22. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 19 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET . 1 0 0 1 0 0 0 with pin A0 connected to ground 1 0 0 1 0 0 1 with pin A0 connected to VDD SX8650 Slave Address(7:1) = Figure 22. I2C slave address Upon request of the customer, a custom I2C address can be burned in the NVM. The host uses the I2C to read and write data and commands to the configuration and status registers. During a conversion, the I2C clock can be stretched until the end of the processing. Channel data read is done by I2C throughput optimized formats. The supported I2C access formats are described in the next sections: I2C Write Registers I2C Read Registers I2C Host Commands I2C Read Channels 5.1.2. I2C Write Registers The format for I2C write is given in Figure 23. After the start condition [S], the SX8650 slave address (SA) is sent, followed by an eighth bit (W=`0') indicating a Write. The SX8650 then Acknowledges [A] that it is being addressed, and the host sends 8-bit Command and Register address consisting of the command bits `000' followed by the SX8650 Register Address (RA). The SX8650 Acknowledges [A] and the host sends the appropriate 8-bit Data Byte (WD0) to be written. Again the SX8650 Acknowledges [A]. In case the host needs to write more data, a succeeding 8-bit Data Byte will follow (WD1), acknowledged by the slave [A]. This sequence will be repeated until the host terminates the transfer with the Stop condition [P]. S SA W A CR A WD0 A A Optional Clock stretching S: SA: W: A: CR: WDn: P: WD1 Start condition SX8650 Slave Address(7:1) '0' Acknowledge '000' + Register Address(4:0) Write Data byte(7:0), 0...n Stop condition WDn A P Optional From host to SX8650 From SX8650 to host Figure 23. I2C write register Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 20 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET The register address increments automatically when successive register data (WD1...WDn) is supplied by the host. This automatic increment can be used for the first 4 register addresses (see Table 6). The correct sampling of the screen by the SX8650 and the host I2C bus traffic are events that might occur simultaneously. The SX8650 will synchronize these events by the use of clock stretching if that is required. The stretching occurs directly after the last received command bit (see Figure 23). 5.1.3. I2C Read Registers The format for incremental I2C read for registers is given in Figure 24. The read has to start with a write of the read address. After the start condition [S], the SX8650 Slave Address (SA) is sent, followed by an eighth bit (W=`0') indicating a Write. The SX8650 then Acknowledges [A] that it is being addressed, and the host responds with a 8-bit CR Data consisting of `010' followed by the Register Address (RA). The SX8650 responds with an Acknowledge [A] and the host sends the Repeated Start Condition [Sr]. Once again, the SX8650 Slave Address (SA) is sent, followed by an eighth bit (R=`1') indicating a Read. The SX8650 responds with an Acknowledge [A] and the read Data byte (RD0). If the host needs to read more data it will acknowledge [A] and the SX8650 will send the next read byte (RD1). This sequence can be repeated until the host terminates with a NACK [N] followed by a stop [P]. S SA W A CR A Sr SA R A RD0 A RD1 A RDn N P Optional S: Sr: SA: W: R: A: N: CR: RDn: P: Start Condition Repeated Start Condition SX8650 Slave Address(7:1) '0' '1' ACKnowledge Not ACKnowledge (terminating read stream) '010' + Register Address(4:0) Read Data byte(7:0), 0...n Stop Condition From Host to SX8650 From SX8650 to Host Figure 24. I2C read registers The I2C read register format of Figure 24 is maintained until the Stop Condition. After the Stop Condition the SX8650 is performing succeeding reads by the compact read format of the I2C read channels described in the next section. No clock stretching will occur for the I2C read registers. 5.1.4. I2C Host Commands The format for I2C commands is given in Figure 25. After the start condition [S], the SX8650 Slave Address (SA) is sent, followed by an eighth bit (W=`0') indicating a Write. The SX8650 then Acknowledges [A] that it is being addressed, and the host responds with an 8-bit Data consisting of a `1' + command(6:0). The SX8650 Acknowledges [A] and the host sends a stop [P]. The exact definition of command(6:0) can be found in Table 8. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 21 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET S SA W A CR A P Clock stretching S: SA: W: A: CR: P: Start condition SX8650 Slave Address(7:1) '0' Acknowledge '1' + Command(6:0) Stop condition From host to SX8650 From SX8650 to host Figure 25. I2C host command The sampling of the screen by the SX8650 and the host I2C bus traffic are events that might occur simultaneously. The SX8650 will synchronize these events by the use of clock stretching if that is required. The stretching occurs directly after the last received command bit (see Figure 25). 5.1.5. I2C Read Channels The host is able to read the channels with a high throughput, by the format shown in Figure 26. After the start condition [S], the SX8650 Slave Address (SA) is sent, followed by an eighth bit (R=`1') indicating a read. The SX8650 responds with an Acknowledge [A] and the Read Data byte (RD0). The host sends an Acknowledge [A] and the SX8650 responds with the Read Data byte (RD1). If the host needs to read more data, it will acknowledge [A] and the SX8650 will send the next read bytes. This sequence can be repeated until the host terminates with a NACK [N] followed immediately by a stop [P]. The NACK [N] releases the NIRQ line. The stop [P] must occur before the end of the conversion. The channel data that can be read is defined by the last conversion sequence. A maximum number of 10 data bytes is passed when all channels (X, Y, z1, z2 and AUX) are activated in the "I2CRegChanMsk". The channel data is sent with the following order: X, Y, Z1, Z2, AUX. The first byte of the data contains the channel information as shown in Figure 27. Typical applications require only X and Y coordinates, thus only 4 bytes of data will be read. S SA R A RD0 A RD1 A RDn-1 A Channel (i) Clock stretching S: SA: R: A: N: RDn: P: Start condition SX8650 Slave Address(7:1) '1' Acknowledge Not Acknowledge (terminating read stream) Read Data byte(7:0), 0...n Stop condition RDn N P Channel (i+1) From host to SX8650 From SX8650 to host Figure 26. I2C read channels Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 22 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET The sampling of the screen by the SX8650 and the host I2C bus traffic are events that might occur simultaneously. The SX8650 will synchronize these events by the use of clock stretching if that is required. The stretching occurs directly after the address and read bit have been sent for the I2C read channels command (see Figure 26). 5.1.6. Data Channel Format Channel data is coded on 16 bits as shown in Figure 27 0 C H A N (2:0) D (7:0) D (11:8) RD1 RD0 Figure 27. data channel format The 3 bits CHAN(2:0) are defined in Table 9 and show which channel data is referenced. The channel data D(11:0) is of unsigned format and corresponds to a value between 0 and 4095. 5.1.7. Invalid Qualified Data The SX8650 will return 0xFFFF data in case of invalid qualified data. This occurs: when the SX8650 converted channels and the host channel readings do not correspond. E.g. the host converts X and Y and the host tries to read X, Y and z1 and z2. when a conversion is done without a pen being detected. 5.2. I2C Register Map I2C register address RA(4:0) Register Description 0 0000 I2CRegCtrl0 Write, Read 0 0001 I2CRegCtrl1 Write, Read 0 0010 I2CRegCtrl2 Write, Read 0 0100 I2CRegChanMsk Write, Read 0 0101 I2CRegStat Read 1 1111 I2CRegSoftReset Write Table 5. I2C Register address The details of the registers are described in the next sections. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 23 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 5.3. Host Control Writing The host control writing allows the host to change SX8650 settings. The control data goes from the host towards the SX8650 and may be read back for verification. register bits default description Set rate in coordinates per sec (cps) ( 20%) If RATE equals zero then Manual mode. if RATE is larger than zero then Automatic mode 7:4 0000 0000: Timer disabled -Manual mode 0001: 10 cps 0010: 20 cps 0011: 40 cps 0100: 60 cps 0101: 80 cps 0110: 100 cps 0111: 200 cps RATE I2CRegCtrl0 1000: 300 cps 1001: 400 cps 1010: 500 cps 1011: 1k cps 1100: 2k cps 1101: 3k cps 1110: 4k cps 1111: 5k cps Settling time ( 10%): The channel will be biased for a time of POWDLY before each channel conversion 3:0 7:6 0000 00 POWDLY 0000: Immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms 00: AUX is used as an analog input 01: On rising AUX edge, wait POWDLY and start acquisition 10: On falling AUX edge, wait POWDLY and start acquisition 11: On rising and falling AUX edges, wait POWDLY and start acquisition AUXAQC The AUX trigger requires the manual mode. I2CRegCtrl1 5 1 CONDIRQ 4 0 reserved 3:2 1:0 00 00 Enable conditional interrupts 0: interrupt always generated at end of conversion cycle. If no pen is detected the data is set to `invalid qualified'. 1: interrupt generated when pen detect is successful RPDNT Select the Pen Detect Resistor 00: 100 KOhm 01: 200 KOhm 10: 50 KOhm 11: 25 KOhm FILT Digital filter control 00: Disable 01: 3 sample averaging 10: 5 sample averaging 11: 7 sample acquisition, sort, average 3 middle samples Table 6. I2C registers Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 24 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET register bits default 7:4 0 description reserved Settling time while filtering ( 10%) When filtering is enabled, the channel will initially bias for a time of POWDLY for the first conversion, and for a time of SETDLY for each subsequent conversion in a filter set. 0000: Immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us I2CRegCtrl2 I2CRegChanMsk 3:0 0000 SETDLY 7 1 XCONV 0: no sample 1: sample, report X channel 6 1 YCONV 0: no sample 1: sample, report Y channel 5 0 Z1CONV 0: no sample 1: sample, report Z1 channel 4 0 Z2CONV 0: no sample 1:sample, report Z2 channel 3 0 AUXCONV 0: no sample 1: sample, report AUX channel 0 0 reserved 0 0 reserved 0 0 reserved 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms The host status reading allows the host to read the status of the SX8650. The data goes from the SX8650 towards the host. Host writing to this register is ignored. I2CRegStat 7 0 CONVIRQ 0: no IRQ pending 1: End of conversion sequence IRQ pending IRQ is cleared by the I2C channel reading 6 0 PENIRQ operational in pen detect mode 0: no IRQ pending 1: Pen detected IRQ pending IRQ is cleared by the I2C status reading 5:0 I2CRegSoftReset 7:0 000000 reserved 0x00 If the host writes the value 0xDE to this register, then the SX8650 will be reset. Any other data will not affect the SX8650 Table 6. I2C registers Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 25 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 5.4. Host Commands The host can write to and read from registers of the SX8650 by the write and read commands as defined in Table 7. W/R command name CR(7:0) 4 Function 7 6 5 3 2 1 0 WRITE(RA) 0 0 0 RA(4:0) Write register (see Table 5 for RA) READ(RA) 0 1 0 RA(4:0) Read register (see Table 5 for RA) Table 7. I2C W/R commands .The host can issue commands to change the operation mode or perform manual actions as defined in Table 8. command name CR(7:0) Function 7 6 5 4 3 2 1 0 SELECT(CHAN) 1 0 0 0 x CHAN(2:0) Bias channel (see Table 9 for CHAN) CONVERT(CHAN) 1 0 0 1 x CHAN(2:0) Bias channel (see Table 9 for CHAN) Wait POWDLY settling time Run conversion MANAUTO 1 0 1 1 x x x x Enter manual or automatic mode. PENDET 1 1 0 0 x x x x Enter pen detect mode. PENTRG 1 1 1 0 x x x x Enter pen trigger mode. Table 8. I2C commands The channels are defined as in Table 9. Channel CHAN(2:0) Function 2 1 0 X 0 0 0 X channel Y 0 0 1 Y channel Z1 0 1 0 First channel for pressure measurement Z2 0 1 1 Second channel for pressure measurement AUX 1 0 0 Auxiliary channel reserved 1 0 1 reserved 1 1 0 SEQ 1 1 1 Channel sequentially selected from I2CRegChanMsk register, (see Table 8) Table 9. channel definition Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 26 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 5.5. Power-Up The NIRQ pin is kept low during SX8650 power-up. voltage During power-up, the SX8650 is not accessible and I2C communications are ignored. VDD VDD/2 time After startup, the host must wait tpor before any communication with the SX8650. t POR voltage As soon as NIRQ rises, the SX8650 is ready for I2C communication. The POR of the SX8650 will reset all registers and states of the SX8650 at power-up. NIRQ time Figure 28. Power-up, NIRQ 5.6. Reset Additionally the host can reset the SX8650 by asserting the NRST pin (active low) and also via the I2C bus. voltage NRST t NRST time voltage If NRST is driven LOW, then NIRQ will be driven low by the SX8650. When NRST is released (or set to high) then NIRQ will be released by the SX8650. The circuit has also a soft reset capability. When writing the code 0xDE to the register RegSoftReset, the circuit will be reset. NIRQ t POR time Figure 29. Reset 6. Modes of Operation The SX8650 has four operation modes that are configured using the I2C commands as defined in Table 8 and Table 6. These 4 modes are: manual (command `MANAUTO' and RATE=0), automatic (command `MANAUTO' and RATE>0), pen detect (command `PENDET'), pen trigger mode (command `PENTRG'). At startup the SX8650 is set in manual mode. In the manual mode the SX8650 is entirely stopped except for the I2C peripheral which accepts host commands. This mode requires RATE equal to be zero (RATE = 0, see Table 6). Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 27 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET In the automatic mode the SX8650 will sequence automatic channel conversions. This mode requires RATE to be larger than zero (RATE > 0, see Table 6). In the PENDET mode the pen detection is activated. The SX8650 will generate an interrupt (NIRQ) upon pen detection and set the PENIRQ bit in the I2C status register. To quit the PENDET mode the host needs to configure the manual mode. In the PENTRG mode the pen detection is activated and a channel conversion will start after the detection of a pen. The SX8650 will generate an interrupt (NIRQ) upon pen detection and set the CONVIRQ bit in the I2C status register. To quit the PENTRIG mode the host needs to configure the manual mode. The PENTRG mode offers the best compromise between power consumption and coordinate throughput. 6.1. Manual Mode In manual mode (RATE=0) single actions are triggered by the I2C commands described in Table 10. When a command is received, the SX8650 executes the associated task and waits for the next command. It is up to the host to sequence all actions. Command CONVERT(CHAN) Action Select and bias a channel Wait for the programmed settling time (POWDLY) Start conversion SELECT(CHAN) Select and bias a channel Table 10 CONVERT and SELECT command The channel can be biased for an arbitrary amount of time by first sending a SELECT command and then a CONVERT command once the settling time requirement is met. The SELECT command can be omitted if the large range of POWDLY settings cover the requirements. In the latter case, the CONVERT command alone is enough to perform an acquisition. With CHAN=SEQ, multiple channels are sampled. This requires programming the POWDLY field in register RegCTRL0. The selected channel will be powered during POWDLY before a conversion is started. The channel bias is automatically removed after the conversion has completed. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 28 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 6.2. Automatic mode In automatic mode (RATE > 0), SX8650 will automatically decide when to start acquisition, sequence all the acquisitions and alerts the host if data is available for download with a NIRQ. The host will read the channels and the SX8650 will start again with the next conversion cycle. AUTO MODE The fastest coordinate rate is obtained if the host reads the channels immediately after the NIRQ. yes CONDIRQ=1 ? Touch Detected ? To not loose data, the SX8650 will not begin conversion before the host read the channels. If after the NIRQ a delay superior to the sampling period is made by the host to read the channels a slower coordinate rate is obtained. When the control CONDIRQ bit (see register I2CRegStat Table 6) is set to `1' then the interrupts will only be generated if the pen detect occurred. This result in a regular interrupt stream, as long as the host performs the read channel commands, and the screen is touched. When the screen is not touched, interrupts does not occur. no yes Set timer=RATE Start timer Start channel conversion If the control CONDIRQ bit is cleared to `0', the interrupts will always be generated. In case there is no pen detected on the screen then the coordinate data will be qualified as invalid, see section [5.1.7]. This result in a regular interrupt stream, as long as the host performs the read channel commands, independent of the screen being touched or not. All conversion finished Set interrupt NIRQ=0 All channel data read This working is illustrated in Figure 30. Release Interrupt NIRQ=1 Timer expire Figure 30. AUTO Mode Flowchart Figure 31 shows the I2C working in automatic mode. After the first sentence send throught the I2C to make the initialization, traffic is reduced as only reads are required. The processing time is the necessary time for the SX8650 to makes the pendetection, the settling time (POWDLY) and the conversion. This time increases with the number of channel selected and the filter used.All succeeding conversions notifies the host by an interrupt signal and the host only needs to issue the I2C read command. TOUCH NIRQ I2C Read Channels Conversion time Time is 1/ RATE NAK The reads occur at the RATE interval. Figure 31. Revision V2.19/October 2010 (c)2010 Semtech Corp. I2C working in AUTO mode Page 29 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 6.3. PENDET Mode The PENDET mode can be used if the host only needs to know if the screen has been touched or not and take from that information further actions. When pen detect circuitry is triggered the interrupt signal NIRQ will be generated and the status register bit `PENIRQ' will be set. The bit is cleared by reading the status register RegStat. PENDET MODE Touch Detected ? no yes Set interrupt NIRQ=0 RegStat read Release Interrupt NIRQ=1 Figure 32. PENDET Mode Flowchart 6.4. PENTRIG Mode The PENTRIG mode offers the best compromise between power consumption and coordinate throughput. In this mode the SX8650 will wait until a pen is detected on the screen and then starts the coordinate conversions. The host will be signalled only when the screen is touched and coordinates are available. The coordinate rate in pen trigger mode is determined by the speed of the host reading the channels and the conversion times of the channels. The host performs the minimum number of I2C commands in this mode. The host has to wait for the NIRQ interrupt to make the acquisition of the datas. The flowchart and the I2C working is illustrated in Figure 33. Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 30 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET PENTRIG MODE Touch Detected ? no TOUCH yes NIRQ Start channel conversion All conversion finished I2C bus I2C Read Channels Set interrupt NIRQ=0 Conversion time NAK All channel data read Release Interrupt NIRQ=1 Figure 33. PENTRIG Mode Flowchart and I2C working in PENTRIG mode 7. Application Information This section describes in more detail application oriented data. 7.1. Acquisition Setup Prior to an acquisition, the SX8650 can be setup by writing the control registers. Registers are written by issuing the register write command. They can be read by issuing the read command. Please refer to the section [5.3]. If no registers are written, the circuit will start in manual mode. 7.2. Channel Selection The SX8650 can be setup to start a single channel conversion or to convert several channels in sequence. For a single conversion, the channel to be converted is determined from the CHAN(2:0) field in the command word (defined in Table 9). Several channels can be acquired sequentially by setting the CHAN(2:0) field to SEQ. The channels will be sampled in the order defined by register RegChanMsk from MSB to LSB. If a "one" is written in a channel mask, the corresponding channel will be sampled, in the opposite case, it is ignored and the next selected channel is chosen. 7.3. Noise Reduction A noisy environment can decrease the performance of the controller. For example, an LCD display located just under the touch screen can adds a lot of noise on the high impedance A/D converter inputs. 7.3.1. POWDLY In order to perform correct coordinates acquisition properly, some time must be given for the touch screen to reach a proper level. It is a function of the PCB trace resistance connecting the SX8650 to the touchscreen and also the capacitance of the touchscreen. If tau is this RC time constant then POWDLY duration must be programmed to 10 tau to reach 12 bit accuracy. Adding a capacitor from the touch screen drivers to ground is a solution to minimize external noise. A low-pass filter created by the capacitor may increase settling time. Therefore, use POWDLY to stretch the acquisition period. POWDLY can be estimated by the following formula : Revision V2.19/October 2010 (c)2010 Semtech Corp. PowDly = 10 x Rtouch x Ctouch Page 31 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET Rtouch is the sum of the panel resistances plus any significant series input resistance, Rxtot + Rytot + Ri. Ctouch is the sum of the touch panel capacitance plus any noise filtering and routing capacitances. 7.3.2. SETDLY A second method of noise filtering uses an averaging filter as described in section [5] (Data processing). In this case, the chip will sequence up to 7 conversions on each channel. The parameter SETDLY sets the settling time between the consecutive conversions. X+ Start of the conversion 5 successive conversions POWDLY In most applications, SETDLY can be set to 0. In some particular applications, where accuracy of 1LSB is required and Ctouch is less than 100nF a specific value should be determined. SETDLY time Figure 34. POWDLY and SETDLY timing with FILT=2 7.3.3. AUX Input An alternate conversion trigger method can be used if the host system provides additional digital signals that indicate noisy or noise-free periods. The SX8650 can be set up to start conversions triggered by the AUX pin. A rising edge, a falling edge or both can trigger the conversion. To enter this mode, AUXACQ must be set to a different value than '00' as defined in Table 6. The AUX edge will first trigger the bias delay (POWDLY). Following the programmed delay, the channel acquisition takes place. 7.4. Interrupt Generation An interrupt (NIRQ=0) will be generated: During the power-up phase or after a reset After completion of a conversion in MANUAL, PENTRIG or AUTO mode. CONVIRQ (bit [7] of RegStat) will be set at the same time. After a touch on the panel is detected in PENDET mode. PENIRQ (bit [6] of RegStat) will be set at the same time. The NIRQ will be released and pulled high(NIRQ=1) by the external pull-up resistor: When the power-up phase is finished When the host read all channels data that were previously converted by the SX8650 in MANUAL, PENTRIG or AUTO mode. CONVIRQ will be cleared at the same time. When the host read the status register in PENDET mode. PENIRQ, will be cleared at the same time. An active NIRQ (low) needs to be cleared before any new conversions will occur. 7.5. Coordinate Throughput Rate The coordinate throughput rate depends on the following factors: The I2C communication time : Tcom The conversion time : Tconv 1 The coordinate rate is the frequency to get the X, Y, Z1 and Z2 coordinate: CoordRate = ------------------------------T com + T conv Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 32 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 7.5.1. I2C Communication Time The minimun time to read the channel data in PENTRIG mode is : T com = ( 8 + 16 x N chan ) x T SPI The highest throughput will be obtained with a I2C frequency of 5MHz when the host read the channel data as quickly as possible after the NIRQ falling edge. 7.5.2. Conversion Time The maximum possible throughput can be estimated with the following equation Tconv ( us ) = 47 Tosc + N chan ( POWDLY + ( N filt - 1 ) SETDLY + ( 21N filt + 1 ) Tosc ) with: Nfilt = {1,3,5,7} based on the order defined for the filter FILT (see Figure 4). Nchan = {1,2,3,4,5} based on the number of channels defined in RegChanMsk POWDLY = 0.5us to 18.19ms, settling time as defined in RegCtrl0 SETDLY = 0.5us to 18.19ms, settling time when filtering as defined in RegCtrl2 Tosc is the oscillator period (555ns +/- 15%) Table 11 gives some examples of Coordinate Rate and Sample Rate for various setting in PENTRIG mode. Nch [1..5 ] Nfilt [1 3 5 7] PowDly [uS] SetDly [uS] Tconv [uS] Tcomm [uS] 2.0 1.0 0.5 0.5 51.7 91.2 2.0 3.0 35.5 0.5 170.6 2.0 5.0 2.2 0.5 4.0 3.0 35.5 0.5 Total [uS] CR [kCPS] ECR [kCPS] SR [kSPS] ESR [kSPS] 142.9 7.0 14.0 7.0 14.0 91.2 261.8 3.8 7.6 11.5 22.9 152.8 91.2 244.0 4.1 8.2 20.5 41.0 315.0 181.2 496.2 2.0 8.1 6.0 24.2 Table 11Coordinate throughput examples 7.5.3. AUTO MODE In AUTO mode, the coordinate throughput rate is the RATE set in RegCtrl0 if the host retrieve channel data at this RATE. The RATE set should be superior or equal to the CoordRate. 7.6. ESD event In case of ESD event, the chip can reset to protect its internal circuitry. Polling a register may be used to check the chip reset event. ESD event may trig the pen detection circuitry. In this case wrong data will be send to the host. To detect this false coordinates on 4-wire touchscreen, a pressure measurement can be done. When reading the values Z1<10 and Z2>4070, the data may not be valid and indicate an ESDevent or a Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 33 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 7.7. Application Schematic A typical application schematic is shown in Figure 35 VDD SX8651 VDD 0.1 uF VDD_HOST AUX VDD_HOST POR OSC R1 R2 R3 R4 NRST 2.2k 2.2k 2.2k X+ A0 2.2k Control I2C HOST DO XYTOUCH SCREN GND SCL Touch Screen Interface Vref ref+ in ADC out ref- Figure 35. SDA Digital Filter NIRQ SCL SDA I2C Interface Y+ INT Typical application VDD_HOST can be higher than VDD but must not exceed the maximun voltage of 3.7V. The host GPIO D0 output is connected to the SX8650 NRST input to allows SX8650 hardware reset. The host D0 may be a totem pole output. In this configuration and if the host and the SX8650 are supply with the same VDD, the R1 pull-up resistor is not required. NIRQ pin is connected to a host interrupt pin. Once NIRQ event happens, the host read the data by a I2C read register. 7.8. Application Examples 7.8.1. Soft Keyboard A keyboard application can be designed with the help of the SX8650. The data are entered by tapping keys on the keyboard with a stylus. The SX8650 send the key coordinates to the microcontroller which interpret them as a symbol. When the keyboard is not activated, the chip stays in low power mode to save power. Figure 36. Keyboard 7.8.2. Slider Controls Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 34 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET Every kind of controls such as rotative knob, slider, button could be emulated with a SX8650 associated to a touchscreen. Figure 37. Slider controls 7.8.3. Game Many kinds of game can be designed with touchscreen. With its high data throughput and its ability to sense pressure, SX8650 is the perfect controller for this kind of application. Figure 38. Game 7.8.4. Handwriting Application An handwriting application needs a powerful microcontroller to run recognition algorithms. The SX8650 includes a preprocessing block to reduce host activity. Figure 39. Handwriting application Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 35 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 8. Packaging Information 8.1. DFN Package D A DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX B A A1 A2 b D D1 E E1 e L N aaa bbb E PIN 1 INDICATOR (LASER MARK) A .028 .000 .030 .031 .001 .002 (.008) .006 .008 .010 .114 .118 .122 .074 .079 .083 .114 .118 .122 .042 .048 .052 .018 BSC .012 .016 .020 12 .003 .004 0.70 0.00 0.75 0.80 0.02 0.05 (0.20) 0.15 0.20 0.25 2.90 3.00 3.10 1.87 2.02 2.12 2.90 3.00 3.10 1.06 1.21 1.31 0.45 BSC 0.30 0.40 0.50 12 0.08 0.10 SEATING PLANE aaa C C A1 A2 D1 1 2 e/2 LxN E/2 E1 N e bxN D/2 bbb C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS. Figure 40. DFN Package Outline Drawing Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 36 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET K DIM (C) Z G H Y X P C G H K P X Y Z DIMENSIONS INCHES MILLIMETERS (.112) .075 .055 .087 .018 .010 .037 .150 (2.85) 1.90 1.40 2.20 0.45 0.25 0.95 3.80 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. 3. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. Figure 41. DFN Package Land Pattern Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 37 www.semtech.com SX8650 World's Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD ADVANCED COMMUNICATIONS & SENSING DATASHEET 8.2. WLCSP Package B 1.50.10 A INDEX AREA A1 CORNER 2.00.10 0.10 C 0.625 Max. 0.250.02 SEATING PLANE C 1.00 0.08 C 0.50 D 0.50 C 1.50 B 0.25 A 1 2 3 12X O0.3150.03 0.05 C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS Figure 42. WLCSP Package Outline Drawing 1.00 0.50 0.50 0.25 1.50 12X O0.25 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS 2. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Figure 43. WLCSP Land Pattern Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 38 www.semtech.com SX8650 DATASHEET ADVANCED COMMUNICATIONS & SENSING (c) S e m te c h 2 0 1 0 A ll rig h ts re s e rv e d . R e p ro d u c tio n in w h o le o r in p a rt is p ro h ib ite d w ith o u t th e p rio r w ritte n c o n s e n t o f th e c o p y rig h t o w n e r. T h e in fo rm a tio n p re s e n te d in th is d o c u m e n t d o e s n o t fo rm p a rt o f a n y q u o ta tio n o r c o n tra c t, is b e lie v e d to b e a c c u ra te a n d re lia b le a n d m a y b e c h a n g e d w ith o u t n o tic e . N o lia b ility w ill b e a c c e p te d b y th e p u b lis h e r fo r a n y c o n s e q u e n c e o f its u s e . P u b lic a tio n th e re o f d o e s n o t c o n v e y n o r im p ly a n y lic e n s e u n d e r p a te n t o r o th e r in d u s tria l o r in te lle c tu a l p ro p e rty rig h ts . S e m te c h a s s u m e s n o re s p o n s ib ility o r lia b ility w h a ts o e v e r fo r a n y fa ilu re o r u n e x p e c te d o p e ra tio n re s u ltin g fro m m is u s e , n e g le c t im p ro p e r in s ta lla tio n , re p a ir o r im p ro p e r h a n d lin g o r u n u s u a l p h y s ic a l o r e le c tric a l s tre s s in c lu d in g , b u t n o t lim ite d to , e x p o s u re to p a ra m e te rs b e y o n d th e s p e c ifie d m a x im u m ra tin g s o r o p e ra tio n o u ts id e th e s p e c ifie d ra n g e . S E M T E C H P R O D U C T S A R E N O T D E S IG N E D , IN T E N D E D , A U T H O R IZ E D O R W A R R A N T E D T O B E S U IT A B L E F O R U S E IN L IF E -S U P P O R T A P P L IC A T IO N S , D E V IC E S O R S Y S T E M S O R O T H E R C R IT IC A L A P P L IC A T IO N S . IN C L U S IO N O F S E M T E C H P R O D U C T S IN S U C H A P P L IC A T IO N S IS U N D E R S T O O D T O B E U N D E R T A K E N S O L E L Y A T T H E C U S T O M E R 'S O W N R IS K . S h o u ld a c u s to m e r p u rc h a s e o r u s e S e m te c h p ro d u c ts fo r a n y s u c h u n a u th o riz e d a p p lic a tio n , th e c u s to m e r s h a ll in d e m n ify a n d h o ld S e m te c h a n d its o ffic e rs , e m p lo y e e s , s u b s id ia rie s , a ffilia te s , a n d d is trib u to rs h a rm le s s a g a in s t a ll c la im s , c o s ts d a m a g e s a n d a tto rn e y fe e s w h ic h c o u ld a ris e . A ll re fe re n c e d b ra n d s , p ro d u c t n a m e s , s e rv ic e n a m e s a n d tra d e m a rk s a re th e p ro p e rty o f th e ir re s p e c tiv e o w n e rs . Contact information Semtech Corporation Advanced Communications & Sensing Products E-mail: sales@semtech.comacsupport@semtech.comInternet: http://www.semtech.com USA 200 Flynn Road, Camarillo, CA 93012-8790. Tel: +1 805 498 2111 Fax: +1 805 498 3804 FAR EAST 12F, No. 89 Sec. 5, Nanking E. Road, Taipei, 105, TWN, R.O.C. Tel: +886 2 2748 3380 Fax: +886 2 2748 3390 EUROPE Semtech Ltd., Units 2 & 3, Park Court, Premier Way, Abbey Park Industrial Estate, Romsey, Hampshire, SO51 9DN. Tel: +44 (0)1794 527 600 Fax: +44 (0)1794 527 601 ISO9001 CERTIFIED Revision V2.19/October 2010 (c)2010 Semtech Corp. Page 39 www.semtech.com