RT9285A/B Preliminary Tiny Package, High Performance, Diode Embedded White LED Driver General Description Features The RT9285 is a high frequency asynchronous boost converter with internal diode, which can support 2 to 5 White LEDs for backlighting and OLED power supply. The Internal soft start function can reduce the inrush current. The device operates with 1MHz fixed switching frequency to allow small external components and to simplify possible EMI problems. The device comes with 20V over voltage protection to allow inexpensive and small-output capacitors with lower voltage rating. The LED current is initially set with the external sense resistor RSET , and the feedback voltage is 250 mV. Tiny package type TSOT-23-6 and WDFN-8L 2x2 packages provide the best solution for PCB space saving and total BOM cost. l l l l l l l l l l l Applications l Ordering Information l RT9285 l Package Type QW : WDFN-8L 2x2 (W-Type) J6 : TSOT-23-6 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) VIN Operating Range : 2.7V to 5.5V Up to 85% Efficiency 22V Internal Power N-MOSFET 1MHz Switching Frequency Built-in Diode Digital Dimming with Zero-Inrush Input UVLO Protection Output Over Voltage Protection Internal Soft Start and Compensation TSOT-23-6 and 8-Lead WDFN Package RoHS Compliant and 100% Lead (Pb)-Free l l l Cellular Phones Digital Cameras PDAs and Smart Phones Porbable Instruments MP3 Player OLED Power Pin Configurations Dimming A : Digital Pulse Dimming B : PWM Clock Dimming (TOP VIEW) VDD VOUT EN Note : Richtek Pb-free and Green products are : }RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. }Suitable for use in SnPb or Pb-free soldering processes. }100%matte tin (Sn) plating. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area, otherwise visit our website for detail. DS9285A/B-02 August 2007 AGND LX NC PGND 1 2 3 4 8 9 7 6 5 FB EN VOUT VDD WDFN-8L 2x2 6 5 4 1 2 3 LX GND FB TSOT-23-6 Note : There is no pin1 indicator on top mark for TSOT-23-6 type, and pin 1 will be lower left pin when reading top mark from left to right. www.richtek.com 1 RT9285A/B Preliminary Typical Application Circuit L1 10uH to 22uH VIN 2.7V to 5.5V RT9285A/B LX EN C1 1uF VDD VOUT Chip Enable GND C2 0.22uF to 1uF FB RSET 12.5 Functional Pin Description Pin No. Pin Name Pin Function WDFN-8L TSOT-23-6 1 -- AGND 2 1 LX -- 2 GND Ground Pin. 3, Exposed Pad (9) -- NC No Internal Connection. 4 -- PGND Power Ground Pin. 5 6 VDD 6 5 VOUT 7 4 EN Analog Ground Pin. LX Pin. Connect this Pin to an inductor. Minimize the track area to reduce EMI. Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input ripple. Output Voltage pin. The pin internally connects to OVP diode to limit output voltage while LEDs are disconnected. Chip Enable (Active High). Note that this pin has an internal pull-down resistance around 300k. Feedback Pin. Series connecting a resistor between WLED and 8 3 FB ground as a current sense. Sense the current feedback voltage to set the current rating. -- www.richtek.com 2 GND Exposed pad should be soldered to PCB board and connected to GND. DS9285A/B-02 August 2007 RT9285A/B Preliminary Function Block Diagram 1.0MHz OSC Current Sense Slope Compensation OCP LX PWM Logic OVP VOUT UVLO/P GOOD VDD EN FB VREF + Timer Dimming Controller Operation Soft-Start The Soft-Start function is made by clamping the output voltage of error amplifier with another voltage source that is increased slowly from zero to near VIN in the Soft-Start period. Therefore, the duty cycle of the PWM will be increased from zero to maximum in this period. The softstart time is decided by a timer of 1.5ms. The charging time of the inductor will be limited as the smaller duty so that the inrush current can be reduced to an acceptable value. + - Soft Start/Cla mping GND In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for RSET selection is shown below. Table 1. RSET Value Selection ILED (mA) RSET () 5 49.9 10 24.9 12 21 15 16.5 20 12.4 Over Voltage Protection Digital Pulse Dimming (RT9285A) The Over Voltage Protection is detected by a junction breakdown detecting circuit. Once VOUT goes over the detecting voltage, LX pin stops switching and the power NMOS is turned off. Then, the VOUT is clamped to be near VOVP. The digital pulse dimming is implemented by checking the low-level duration time of EN pin. As the duration time is in the range of TUP, the LED current will increase 1/16. If the duration time is in the range of TDOWN, the LED current will decrease 1/16. The high-level duration time of EN pin needs larger than TDELAY to make sure the logic can be detected correctly. As the LED current is set to MAX (16/ 16), it will keep MAX until the decreasing signal is detected. On the other hand, as the LED current is set to MIN (1/16), it will keep MIN until the increasing signal is detected. When the chip turns on, the initial state of LED current is MAX. LED Current Setting The RT9285 regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily. ILED (mA) = 0.25/RSET DS9285A/B-02 August 2007 www.richtek.com 3 RT9285A/B Preliminary Table 2 Feedback Voltage Time Symbol Increase 0.5s to 75s TUP Decrease 180s to 300s TDOWN Delay between steps > 0.5s TDELAY Shutdown > 1ms TSHDN TDELAY EN TDOWM TUP TSHDN Shut-down Shut-down 100% 15/16 100% IWLED Figure 1 PWM Dimming (RT9285B) For controlling the LED brightness, the RT9285B can perform the dimming control by applying a PWM signal to EN pin. A low pass filter is implemented inside chip to reduce the slew rate of ILED to prevent the audio noise. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly. EN IWLED, AVG = Duty of EN IWLED Figure 2 Current Limiting The current flow through the inductor as charging period is detected by a current sensing circuit. As the value over the current limiting, the NMOS will be turned-off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase over the current limiting. www.richtek.com 4 DS9285A/B-02 August 2007 RT9285A/B Preliminary Absolute Maximum Ratings (Note 1) Supply Voltage, VIN ------------------------------------------------------------------------------------------------- -0.3 to 6V l LX Input Voltage ------------------------------------------------------------------------------------------------------ - 0.3V to 22V l Output Voltage ------------------------------------------------------------------------------------------------------- - 0.3V to 21V l The other pins -------------------------------------------------------------------------------------------------------- - 0.3V to 6V l Power Dissipation, PD @ TA = 25C TSOT23-6 -------------------------------------------------------------------------------------------------------------- 0.455W WDFN-8L 2x2 --------------------------------------------------------------------------------------------------------- 0.606W l Package Thermal Resistance (Note 4) TSOT23-6, JA -------------------------------------------------------------------------------------------------------- 220C/W WDFN-8L 2x2, JA --------------------------------------------------------------------------------------------------- 165C/W l Junction Temperature ----------------------------------------------------------------------------------------------- 150C l Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------- 260C l Storage Temperature Range --------------------------------------------------------------------------------------- - 65C to 150C l ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V l Recommended Operating Conditions l l (Note 3) Operation Junction Temperature Range ------------------------------------------------------------------------- -40C to 125C Operation Ambient Temperature Range ------------------------------------------------------------------------- -40C to 85C Electrical Characteristics (VIN = 3.7V, FREQ left floating, TA = 25 C, unless otherwise specification) Parameter Symbol Test Condition Min Typ Max Units System Supply Input Operation voltage Range V IN 2.7 -- 5.5 V Under Voltage Lock Out V UVLO 1.7 2 2.3 V Quiescent Current IQ FB = 1.5V, No switch -- 300 450 A Supply Current I IN FB = 0V, Switch -- -- 2 mA Shut Down Current I SHDN VEN < 0.4V -- 2 5 uA V IN = 3V to 4.3V -- -- 3 % -- 1 -- MHz 85 90 -- % 0.237 0.25 0.263 V -- 0.9 -- V 0.5 0.75 1 Output Line Regulation Oscillator Operation Frequency f OSC Maximum Duty Cycle Reference Voltage Feedback Reference Voltage VREF Diode Forward Voltage VFW IFW = 100mA MOSFET On Resistance of MOSFET R DS(ON) To be continued DS9285A/B-02 August 2007 www.richtek.com 5 RT9285A/B Parameter Preliminary Symbol Test Condition Min Typ Max Units -- 20 -- V -- 400 -- mA -- -- 0.4 V 1.4 -- -- V Protection OVP Threshold VOVP OCP Control Interface EN Threshold Logic-Low Voltage VIL Logic-High Voltage VIH Digital Dimming (for RT9285A) Up Brightness Time TUP Refer to Figure 1 0.5 -- 75 s Down Brightness Time TDOWN Refer to Figure 1 180 -- 300 s Delay Between Steps Time TDELAY Refer to Figure 1 0.5 -- -- s Shut Down Delay Time TSHDN Refer to Figure 1 1 -- -- ms Note 1.Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. www.richtek.com 6 DS9285A/B-02 August 2007 RT9285A/B Preliminary Typical Operating Characteristics OVP vs. Input Voltage Efficiency vs. Input Voltage 20.8 90 90% 20.4 85 85% 4W-LED 80 80% Efficiency (%) OVP (V) 20 19.6 19.2 18.8 75 75% 70% 70 65% 65 60% 60 18.4 55% 55 18 50% 50 2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8 6.2 2.5 3 3.5 Input Voltage (V) Quiescent Current vs. Input Voltage 5 5.5 6 Frequency vs. Input Voltage 1.02 1.00 400 -40C 350 25C 300 85C 250 200 Frequency (MHz) Quiescent Current (uA) 4.5 Input Voltage (V) 450 0.98 0.96 0.94 0.92 0.90 150 0.88 100 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 3.1 3.6 Enable Voltage vs. Input Voltage 5.1 5.6 Output Voltage vs. Output Current 0.83 16 0.80 0.79 Shutdown Voltage 0.77 Output Voltage (V) Enable Voltage 0.81 0.78 4.6 17 0.84 0.82 4.1 Input Voltage (V) Input Voltage (V) Enable Voltage (V) 4 15 14 13 12 0.76 11 0.75 0.74 10 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 Input Voltage (V) DS9285A/B-02 August 2007 5 15 25 35 45 55 65 75 Output Current (mA) www.richtek.com 7 RT9285A/B Preliminary Feedback Reference Voltage vs. Input Voltage Dimming Operation @ Decreace Feedback Reference Voltage (mV) 253.5 VIN (2V/Div) VOUT (5V/Div) 253.0 252.5 VIN = 3.7V 252.0 251.5 251.0 EN (2V/Div) 250.5 250.0 ILED (10mA/Div) 249.5 249.0 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 Time (500s/Div) Input Voltage (V) Dimming Operation @ Increase VIN (2V/Div) VOUT (5V/Div) VIN = 3.7V Inrush Current Response VIN (2V/Div) VIN = 3.7V VOUT (5V/Div) EN (2V/Div) EN (2V/Div) IIN (100mA/Div) ILED (10mA/Div) Time (500s/Div) www.richtek.com 8 Time (500s/Div) DS9285A/B-02 August 2007 RT9285A/B Preliminary Application Information LED Current Control The RT9285A/B regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The RT9284A/B feedback voltage (VFB) is 0.25V. The LED current (ILED) can be set by a resistor RSET . ILED = 0.25/RSET In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). L1 10uH to 22uH RT9285A/B LX EN Capacitor Selection Input and output ceramic capacitors of 1F are recommended for RT9285A/B applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Output Voltage Control The output voltage of R9285 can be adjusted by the divider circuit on FB pin. Figure 6 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations in Figure 6. C1 1uF VDD VOUT C2 0.22uF to 1uF Chip Enable GND VIN 2.7V to 5.5V The inductor saturation current rating should be considered to cover the inductor peak current. L1 10uH to 22uH FB VIN 2.7V to 5.5V RSET 12.5 C1 1uF RT9285A/B Figure 3. Application for Driving 4 Series WLEDs L1 10uH to 22uH LX VDD VOUT EN VIN 2.7V to 5.5V VOUT 15V R1 590k C2 0.22uF to 1uF Chip Enable GND FB R2 10k RT9285A/B LX EN VOUT = 0.25 x R1 + R2 ; R2 > 10k R2 VDD Figure 5. Application for Constant Output Voltage VOUT C2 0.22uF to 1uF Chip Enable GND C1 1uF VIN FB RSET 12.5 The recommended value of inductor for 4 to 5WLEDs applications are 10H to 22H. For 3W LEDs, the recommended value of inductor is 4.7H to 22H. Small size and better efficiency are the major concerns for portable device, such as RT9285A/B used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. DS9285A/B-02 August 2007 RT9285A/B VDD Figure 4. Application for Driving 5 Series WLEDs Inductor Selection GPIO VEN VOUT LX FB EN GND RA R GPIO OLED RB Figure 6. Application Circuit for Output Voltage Control and Related Equations www.richtek.com 9 RT9285A/B Preliminary VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB (1) As GPIO = 0V, } LX node copper area should be minimized for reducing EMI. (*1) (2) } The input capacitor C1 should be placed as closed as possible to Pin 6. (*2) VOUT = RA x {(0.25/RB) + (0.25-2.8)/RGPIO )} + 0.25 (3) } The output capacitor C2 should be connected directly from the Pin 5 to ground rather than across the LEDs. (*3) As GPIO = 1.8V, VOUT = RA x {(0.25/RB) + (0.25-1.8)/ RGPIO)} + 0.25 (4) } FB node copper area should be minimized and keep far away from noise sources (Pin 1, Pin 5, Pin 6). (*4) For Efficiency Consideration : } The Inductor is far away receiver and microphone. Set RA = 990k, } The voice trace is far away RT9285. If 2 levels are 16V (GPIO = 0V) and 14V (GPIO = 1.8V) } The embedded antenna is far away and different side RT9285. VOUT = RA x {(0.25/RB) + (0.25/RGPIO)} + 0.25 As GPIO = 2.8V, Get RB = 16k, RGPIO = 890k Table 3. Suggested Resistance for Output Voltage Control RA RB RGPIO Conditions (k) (k) (k) } R1 should be placed as close as RT9285. } The through hole of RT9285's GND pin is recommended as large and many as possible. Case A : L1 VIN C1 Normal Voltage = 16V (GPIO = 0V) *1 1100 18 *2 495 LX 1 6 VDD GND 2 5 VOUT 3 4 EN Dimming Voltage = 12V C2 *3 GND (GPIO = 1.8V) RSET *4 FB Case B : WLEDs EN Normal Voltage = 16V (GPIO = 0V) 1200 19.5 840 Figure 7. TOP Dimming Voltage = 12V (GPIO = 2.8V) Considering the output voltage deviation from the GPIO voltage tolerance, as GPIO voltage vibrated by 0 50mV and 1.8(2.8) 5% ,the output voltage could be kept within 2.5%. Layout guide } A full GND plane without gap break. Figure 8. Bottom } Traces in bold need to be routed first and should be kept as short as possible. } VDD to GND noise bypass : Short and wide connection for the 1uF MLCC capacitor between Pin 6 and Pin 2. www.richtek.com 10 DS9285A/B-02 August 2007 RT9285A/B Preliminary Outline Dimension H D L C B b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-6 Surface Mount Package DS9285A/B-02 August 2007 www.richtek.com 11 RT9285A/B Preliminary D2 D L E2 E 1 e SEE DETAIL A b 2 1 2 1 A A1 A3 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.200 0.300 0.008 0.012 D 1.950 2.050 0.077 0.081 D2 1.000 1.250 0.039 0.049 E 1.950 2.050 0.077 0.081 E2 0.400 0.650 0.016 0.026 e L 0.500 0.300 0.020 0.400 0.012 0.016 W-Type 8L DFN 2x2 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com www.richtek.com 12 DS9285A/B-02 August 2007