19-5011; Rev 2; 4/10 KIT ATION EVALU LE B A IL A AV High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing The MAX9934 high-precision, low-voltage, high-side current-sense amplifier is ideal for both bidirectional (charge/discharge) and unidirectional current measurements in battery-powered portable and laptop devices. Input offset voltage (VOS) is a low 10V (max) at +25C across the -0.1V to 5.5V input common-mode voltage range, and is independent of VCC. Its precision input specification allows the use of very small sense voltages (typically 10mV full-scale) for minimally invasive current sensing. The output of the MAX9934 is a current proportional to input V SENSE and is available in either 25A/mV or 5A/mV gain options (GM) with gain accuracy better than 0.25% (max) at +25C. A chip select (CS) allows multiplexing of several MAX9934 current outputs to a single microcontroller ADC channel (see the Typical Operating Circuit). CS is compatible with 1.8V and 3.3V logic systems. The MAX9934 is designed to operate from a 2.5V to 3.6V VCC supply, and draws just 120A (typ) quiescent current. When powered down (VCC = 0), RS+ and RSdraw less than 0.1nA (typ) leakage current to reduce battery load. The MAX9934 is robust and protected from input faults of up to 6V input differential voltage between RS+ and RS-. The MAX9934 is specified for operation over the -40C to +125C temperature range and is available in an 8-pin MAX(R) or a 6-bump UCSPTM (1mm x 1.5mm x 0.6mm), making it ideal for space-sensitive applications. Applications Features Input Offset Voltage: 10V (max) Gain Error Less than 0.25% -0.1V to +5.5V Input Common-Mode Voltage Range Chip Select Allows Multiplexing Several MAX9934 Current Monitors to One ADC Current Output Allows ROUT Selection for Gain Flexibility Single Supply Operation: 2.5V to 3.6V Two Gain Options: GM of 25A/mV (MAX9934T) and 5A/mV (MAX9934F) Bidirectional or Unidirectional Operation Small, 6-Bump UCSP (1mm x 1.5mm x 0.6mm) and 8-Pin MAX Packages Ordering Information PART PINPACKAGE GAIN MAX9934FART+T TOP MARK 5A/mV 6 UCSP AAG MAX9934FAUA+T 5A/mV 8 MAX -- MAX9934TART+T 25A/mV 6 UCSP AAF MAX9934TAUA+T 25A/mV 8 MAX -- Note: All devices are specified over the -40C to +125C extended temperature range. +Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. PDAs and Smartphones MP3 Players Sensor Instrumentation Amplifiers Notebook PCs and Ultra-Mobile PCs Typical Operating Circuit Portable Current Monitoring VCC = 3.3V 0.1F -0.1V VCM 5.5V ILOAD VCC RSENSE MAX9934 RS- OUT RS+ MAX is a registered trademark and UCSP is a trademark of Maxim Integrated Products, Inc. ROUT 10k GND CS VOUT TO ADC 1000pF FROM C CHIP SELECT ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX9934 General Description MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing ABSOLUTE MAXIMUM RATINGS RS+, RS- to GND......................................................-0.3V to +6V VCC to GND ..............................................................-0.3V to +4V CS, OUT to GND (VCC = 0, or CS < VIL)..................-0.3V to +4V OUT to GND (CS > VIH)................................-0.3V to VCC + 0.3V Differential Input Voltage (RS+ - RS-) ....................................6V Output Short-Circuit Current Duration OUT to GND or VCC ...............................................Continuous Continuous Input Current into Any Terminal.....................20mA Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate multilayer 4.8mW/C above +70C).............................................................388mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) ....................................................................206C/W Junction-to-Case Thermal Resistance (JC) (Note 1) ......................................................................42C/W 6-Bump UCSP (derate multilayer 3.9mW/C above +70C).............................................................308mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) ....................................................................260C/W Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (MAX only, soldering, 10s) ..............+300C Soldering Temperature (reflow) .......................................+260C Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and 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 affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC CHARACTERISTICS MAX9934T Input Offset Voltage (Note 3) VOS MAX9934F Input Offset Voltage Drift (Note 3) VOS/dT Common-Mode Input Voltage Range (Average of VRS+ and VRS-) (Note 3) CMVR CMRR1 Common-Mode Rejection Ratio (Note 3) CMRR2 2 TA = +25C 10 -40C TA +125C 14 TA = +25C 10 -40C TA +125C 20 MAX9934T 60 MAX9934F 90 Guaranteed by CMRR2 -0.1 0 VCM VCC 0.2V (MAX9934F) TA = +25C 128 -40C TA +125C 112 0 VCM VCC 0.2V (MAX9934T) TA = +25C 128 -40C TA +125C 109 -0.1 VCM 5.5V (MAX9934F) TA = +25C 119 -40C TA +125C 104 -0.1 VCM 5.5V (MAX9934T) TA = +25C 98 -40C TA +125C 98 +5.5 V nV/C V 134 135 125 113 _______________________________________________________________________________________ dB High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER Current Gain (Transconductance) SYMBOL GM CONDITIONS MAX9934F 5 GME MAX9934F Gain Error Drift GME/dT Input-Bias Current for RS+ IBRS+ TYP 25 MAX9934T Current Gain Error (Note 4) MIN MAX9934T TA = +25C MAX UNITS A/mV 0.25 -40C TA +125C 2.0 TA = +25C 0.25 -40C TA +125C % 2.4 MAX9934T 200 MAX9934F 240 ppm/C VRS+ = VRS- = 5.5V 0.1 100 VRS+ = VRS- VCC - 0.2V 0.1 100 nA VRS+ = VRS- = 5.5V 35 60 A 0.1 100 nA 1 100 nA Input-Bias Current for RS- IBRS- Input Leakage Current ILEK VCC = 0V, VRS+ = VRS- = 5.5V Minimum Current for Output Low IOL Unidirectional, VOL = IOL x ROUT Output-Voltage Range (MAX9934T) VOH IOUT = +600A, VOH = VCC - VOUT 0.1 0.25 VOL IOUT = -600A, bidirectional 0.15 0.25 Output-Voltage Range (MAX9934F) VOH IOUT = +375A, VOH = VCC - VOUT 0.18 0.30 VOL IOUT = -375A, bidirectional 0.18 0.26 IOLK VCS = 0V, VOUT = 3.6V, and 0 VCC 3.6V 0.1 100 nA DC CHARACTERISTICS Deselected Amplifier Output Leakage V V nA LOGIC I/O (CS) Input Voltage Low CS VIL Input Voltage High CS VIH Input Current CS 0.54 IIL,IIH 0 VCS VCC VCC Guaranteed by PSRR 2.5 2.5V VCC 3.6V, VRS+ = VRS- = 2V (Note 3) 110 V 0.1 1.26 V 100 nA 3.6 V POWER SUPPLY Supply-Voltage Range Power-Supply Rejection Ratio Supply Current PSRR ICC Supply Current, Output Deselected ICC,DES 120 dB VCC = 3.3V, ROUT = 10k to 3.3V, VRS+ = VRS- = 3.1V 120 230 A VCS = 0V, ROUT = 10k to 3.3V, VRS+ = VRS- = 3.1V 120 210 A MAX9934T GM = 25A/mV, VSENSE = 5mV 1.5 MAX9934F GM = 5A/mV, VSENSE = 25mV 5 AC CHARACTERISTICS (CL = 1000pF) Amplifier Bandwidth BW kHz _______________________________________________________________________________________ 3 MAX9934 ELECTRICAL CHARACTERISTICS (continued) MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing ELECTRICAL CHARACTERISTICS (continued) (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, VCM = (VRS+ + VRS-)/2, VCS = 3.3V, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER Output Settling Time Output Select Time SYMBOL tS tZH CONDITIONS MIN TYP 0.1% final value, Figure 1, MAX9934T 670 0.1% final value, Figure 1, MAX9934F 220 Output to 0.1% final value, Figure 2, MAX9934T 150 MAX UNITS s s Output to 0.1% final value, Figure 2, MAX9934F 80 Output Deselect Time tHZ Output step of 100mV, CL = 10pF, Figure 2 2 s Power-Down Time tPD Output step of -100mV, CL = 10pF, VCC > 2.5V 2 s Power-Up Time tPU 0.1% final value, Figure 3, MAX9934T 300 0.1% final value, Figure 3, MAX9934F 200 s Note 2: All devices are 100% production tested at TA = +25C. Unless otherwise noted, specifications overtemperature are guaranteed by design. Note 3: Guaranteed by design. Thermocouple, contact resistance, RS- input-bias current, and leakage effects preclude measurement of this parameter during production testing. Devices are screened during production testing to eliminate defective units. Note 4: Gain error tested in unidirectional mode: 0.2V VOUT 3.1V for the MAX9934T; 0.25V VOUT 2.5V for the MAX9934F. 4 _______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE MAX9934T DRIFT VOS HISTOGRAM 35 25 20 N (%) 15 15 10 10 TA = +25NC TA = -40NC -4 -2 0 2 4 6 8 10 0 6 -0.1 0.6 12 18 24 30 36 42 48 54 60 1.3 2.0 2.7 3.4 4.1 VOS (FV) TCVOS (nV/NC) COMMON-MODE VOLTAGE (V) OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE MAX9934T GAIN ERROR HISTOGRAM MAX9934T GAIN ERROR DRIFT HISTOGRAM 30 VCC = 3.3V 25 N (%) VCC = 3.6V 15 15 -2 10 0 0 MAX9934F GAIN ERROR HISTOGRAM VOUT vs. VSENSE VREF = GND 20 30 -200 0.20 0.12 0.16 MAX9934F GAIN ERROR DRIFT HISTOGRAM 3.5 MAX9934 toc08 35 TC GE (PPM/NC) 25 MAX9934 toc07 40 GE (%) 3.0 MAX9934 toc09 COMMON-MODE VOLTAGE (V) 0.08 5.5 0 4.8 0.04 4.1 -0.04 3.4 -0.08 2.7 -0.12 2.0 -0.20 1.3 -0.16 -10 80 5 120 5 -8 0 10 40 -6 -40 -4 -0.1 0.6 20 -80 0 N (%) 20 2 -120 VCC = 2.5V 4 25 MAX9934 toc06 6 5.5 35 MAX9934 toc05 30 MAX9934 toc04 8 4.8 200 -4 160 -6 10 OFFSET VOLTAGE (FV) 0 -2 -10 0 -10 -8 GAIN = 25A/mV 2.5 20 15 VOUT (V) N (%) 25 10 15 2.0 GAIN = 5A/mV 1.5 1.0 10 UNIDIRECTIONAL 5 0.5 TC GE (PPM/C) 200 160 80 120 40 0 -40 -80 -120 -160 0 -200 0.20 0.16 0.12 0.08 0 GE (%) 0.04 -0.08 -0.04 -0.12 -0.20 5 -0.16 N (%) 2 -8 0 0 4 -6 5 5 TA = +125NC 6 -160 N (%) 20 8 OFFSET VOLTAGE (FV) 30 25 10 MAX9934 toc02 30 MAX9934 toc01 40 MAX9934 toc03 MAX9934T VOS HISTOGRAM 0 0 10 20 30 40 50 60 70 80 VSENSE (mV) _______________________________________________________________________________________ 5 MAX9934 Typical Operating Characteristics (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.) VOUT vs. VSENSE VREF = 1.65V VOUT vs. VSENSE (VOUT < 5mV) BIDIRECTIONAL 1.5 4 1.0 G = 25FA/mV 0.5 VOUT (mV) VOUT - VREF (V) MAX9934 toc11 5 MAX9934 toc10 2.0 GAIN = 5A/mV 0 GAIN = 25A/mV -0.5 -1.0 3 G = 5FA/mV 2 1 -1.5 -2.0 0 -20 0 20 40 100 80 VOH vs. IOH SUPPLY CURRENT vs. TEMPERATURE (VCS = 0) 160 MAX9934 toc12 MAX9934T 100 140 SUPPLY CURRENT (A) MAX9934F 150 50 VCM = 0V 120 VCM = 5.5V 100 80 60 0 40 100 200 300 400 500 600 -40 -25 -10 5 20 35 50 65 80 95 110 125 IOH (A) TEMPERATURE (C) RS+ BIAS CURRENT vs. VRS+ SUPPLY CURRENT vs. TEMPERATURE 10nA MAX9934 toc14 160 VCM = 0V MAX9934 toc15 0 140 60 VSENSE + VOS (FV) 250 200 20 VSENSE (mV) 300 VOH (mV) 0 40 MAX9934 toc13 -40 TA = +125C 1nA 120 VCM = 5.5V 100 80 RS+ BIAS CURRENT SUPPLY CURRENT (A) MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing 100pA TA = +25C AND -40C 10pA 60 1pA 40 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) 6 -0.1 0.6 1.3 2.0 2.7 3.4 4.1 VRS+ (V) _______________________________________________________________________________________ 4.8 5.5 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing RS- BIAS CURRENT vs. VRS- (-0.1V VRS- VCC) RS- BIAS CURRENT vs. VRS- ( 3V VRS_ 5.5V) 45 40 RS- BIAS CURRENT (A) 10nA 1nA 100pA TA = +25C AND -40C 10pA MAX9934 toc17 TA = +125C RS- BIAS CURRENT (pA) 50 MAX9934 toc16 100nA TA = +125C 35 TA = +25C 30 25 TA = -40C 20 15 10 5 0 1pA 0.4 0.9 1.4 1.9 2.4 2.9 3.0 3.4 3.5 4.0 OUTPUT LEAKAGE CURRENT vs. VOUT (VCS = 0) 1nA TA = +125C 100pA TA = +25C 1pA 10nA OUTPUT LEAKAGE CURRENT MAX9934 toc18 OUTPUT LEAKAGE CURRENT 5.0 5.5 OUTPUT LEAKAGE CURRENT vs. VOUT (VCC = 0, VCS = 0) 10nA 10pA 4.5 VRS- (V) VRS- (V) MAX9934 toc19 -0.1 TA = +125C 1nA 100pA TA = +25C TA = -40C 10pA TA = -40C 100fA 1pA 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 VOUT (V) NORMALIZED GAIN vs. FREQUENCY COMMON-MODE REJECTION RATIO vs. FREQUENCY 10 G = 5FA/mV 0 0 -20 4.0 -40 -10 CMRR (dB) NORMALIZED GAIN (dB) 0 VOUT (V) MAX9934 toc21 0.5 MAX9934 toc20 0 G = 25FA/mV -20 -60 -80 -100 -30 -120 -40 -140 1 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 0.1 1.0 10 100 FREQUENCY (kHz) _______________________________________________________________________________________ 7 MAX9934 Typical Operating Characteristics (continued) (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.) 1.0 MAX9934 toc22 0 1V VOUT STEP 0.9 0.8 SETTING TIME (ms) -20 MAX9934 toc23 OUTPUT SETTING TIME vs. PERCENTAGE OF FINAL VALUE POWER-SUPPLY REJECTION RATIO vs. FREQUENCY -40 PSRR (dB) MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing -60 -80 0.7 0.6 MAX9934T 0.5 0.4 MAX9934F 0.3 0.2 -100 0.1 0 -120 0.01 0.1 1.0 1.00 100 10 0.10 0.01 FREQUENCY (kHz) PERCENTAGE OF FINAL VALUE (%) LARGE-SIGNAL INPUT STEP RESPONSE (MAX9934F) LARGE-SIGNAL INPUT STEP RESPONSE (MAX9934T) MAX9934 toc24 MAX9934 toc25 VSENSE 20mV/div VSENSE 5mV/div 0.01% FINAL VALUE 0.01% FINAL VALUE 2V VOUT 500mV/div 1% FINAL VALUE 1V 2V VOUT 500mV/div 400s/div OUTPUT SELECT TIME CS DISABLED TRANSIENT RESPONSE COUT = 10pF (MAX9934T) MAX9934 toc27 CL = 0 VCS 2V/div 1% FINAL VALUE 1V VCS 2V/div 0.1% FINAL VALUE MAX9934T 1% FINAL VALUE 1V VOUT 500mV/div 0.1% FINAL VALUE MAX9934F 40Fs/div 8 1V 100s/div MAX9934 toc26 VOUT 500mV/div 1% FINAL VALUE VOUT 1V/div 4s/div _______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing SATURATION RECOVERY TIME VOUT = VOL TO 1V (MAX9934T) POWER-UP TIME MAX9934 toc28 MAX9934 toc29 UNIDIRECTIONAL VCS 2V/div VSENSE 5mV/div 1% FINAL VALUE 1mV 1V VOUT 500mV/div 0.1% FINAL VALUE 1% FINAL VALUE MAX9934T 1V VOUT 500mV/div MAX9934F 1V 0.1% FINAL VALUE VOUT 500mV/div CBYPASS = 0.1F 0V 100Fs/div 400Fs/div SATURATION RECOVERY TIME VOUT = VOH TO 1V (MAX9934T) MAX9934 toc30 UNIDIRECTIONAL VSENSE 10mV/div VOUT 1V/div 1V 400s/div _______________________________________________________________________________________ 9 MAX9934 Typical Operating Characteristics (continued) (VCC = 3.3V, VRS+ = VRS- = 3.0V, VSENSE = 0V, CL = 1000pF, ROUT = 10k to GND for unidirectional operation, ROUT = 10k to VCC/2 for bidirectional operation. TA = +25C, unless otherwise noted.) MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing Pin Description PIN/BUMP NAME FUNCTION UCSP MAX A1 1 VCC Power Supply A2 2 OUT Current Output. OUT provides an output current proportional to input VSENSE. Connect an external resistor (ROUT) from OUT to GND for unidirectional sensing or to an external reference voltage for bidirectional sensing. A3 3 GND Ground B1 8 RS+ Sense Resistor Power Side Connection B2 7 RS- Sense Resistor Load Side Connection Chip-Select Input. Drive CS high to enable OUT, drive CS low to put OUT in a high-impedance state. B3 6 CS -- 4, 5 N.C. No Connection. Not internally connected. Functional Diagram CS VSENSE MAX9934 % FINAL VALUE VCC 2V VOUT 1V STEP RS+ Gm Gm RS- % FINAL VALUE *RGAIN OUT 1V tS tS GND *RGAIN = 40 FOR THE MAX9934T AND RGAIN = 200 FOR THE MAX9934F. Detailed Description The MAX9934 high-side, current-sense amplifier monitors current through an external current-sense resistor by amplifying the voltage across the resistor (VSENSE) to create an output current (IOUT). An output voltage (VOUT) then develops across the external output resistor (ROUT). See the Typical Operating Circuit. The MAX9934 uses precision amplifier design techniques to achieve a low-input offset voltage of less than 10V. These techniques also enable extremely low-input offset voltage drift over time and temperature and 10 Figure 1. Output Settling Time achieve gain error of less than 0.25%. The precision VOS specification allows accurate current measurements with a low-value current-sense resistor, thus reducing power dissipation in battery-powered systems, as well as loadregulation issues in low-voltage DC power supplies. The MAX9934 high-side current-sense amplifier features a -0.1V to +5.5V input common-mode range that is independent of supply voltage (VCC). This ability to sense at voltages beyond the supply rail allows the monitoring of currents out of a power supply even in a shorted condition, while also enabling high-side current sensing at voltages greater than the MAX9934 supply ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934 1.8V 3.3V VCS VCC 2.5V 0V 0V % FINAL VALUE % FINAL VALUE tHZ tPD VOUT VOUT 100mV 100mV tZH Figure 2. Output Select and Deselect Time voltage. Further, when VCC = 0, the amplifier maintains an extremely high impedance on both its inputs and output, up to the maximum operating voltages (see the Absolute Maximum Ratings section). The MAX9934 features a CS that can be used to deselect its output current-source. This allows multiple current-sense amplifier outputs to be multiplexed into a single ADC channel with a single ROUT. See the Chip Select Functionality for Multiplexed Systems section for more details. The Functional Diagram shows the internal operation of the MAX9934. At its core is the indirect current-feedback architecture. This architecture uses two matched transconductance amplifiers to convert their input differential voltages into an output current. A high-gain feedback amplifier forces the voltage drop across RGAIN to be the same as the input differential voltage. The internal resistor (RGAIN) sets the transconductance gain of the device. Both input and output transconductance amplifiers feature excellent common-mode rejection characteristics, helping the MAX9934 to deliver industry-leading precision specifications over the full common-mode range. tPU Figure 3. Output Power-Up and Power-Down Time Applications Information Advantages of Current-Output Architecture The transconductance transfer function of the MAX9934 converts input differential voltage to an output current. An output termination resistor, ROUT, then converts this current to a voltage. In a large circuit board with multiple ground planes and multiple current-measurement rails spread across the board, traditional voltage-output current-sense amplifiers become susceptible to ground-bounce errors. These errors occur because the local ground at the location of the current-sense amplifier is at a slightly different voltage than the local ground voltage at the ADC that is sampling the voltage. The MAX9934 allows accurate measurements to be made even in the presence of system ground noise. This is achieved by sending the output information as a current, and by terminating to the ADC ground. A further advantage of current-output systems is the flexibility in setting final voltage gain of the device. Since the final voltage gain is user-controlled by the choice of output termination resistor, it is easy to optimize the monitored load current range to the ADC input voltage range. It is no longer necessary to increase the size of the sense resistor (also increasing power dissipation) as necessary with fixed-gain, voltage-output current-sense amplifiers. ______________________________________________________________________________________ 11 MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing ILOAD1 VCC = 3.3V VIN1 -0.1V VCM 5.5V 0.1F RSENSE OUT1 MAX9934 MICROCONTROLLER CS1 ILOAD2 VIN2 -0.1V VCM 5.5V VCC = 3.3V 0.1F RSENSE OUT2 MAX9934 CS2 ILOAD3 VIN3 -0.1V VCM 5.5V VCC = 3.3V 0.1F RSENSE OUT3 MAX9934 CS3 ADC VOUT UNIDIRECTIONAL OPERATION 10k (OPTIONAL) Figure 4. Typical Application Circuit Showing Chip-Select Multiplexing Chip-Select Functionality for Multiplexed Systems The MAX9934 features a CS that can be used to deselect the output current - source achieving a high-impedance output with 0.1nA leakage current. Thus, different supply voltages can be used to power different MAX9934 devices that are multiplexed on the same bus. This technique makes it possible for advanced current monitoring and power-management schemes to be implemented when a limited number of ADC channels are available. In a multiplexed arrangement, each MAX9934 is typically placed near the load being monitored and all 12 amplifier outputs are connected in common to a single load resistor located adjacent to the monitoring ADC. This resistor is terminated to the ADC ground reference as shown in Figure 4 for unidirectional applications. Figure 5 shows a bidirectional multiplexed application. Terminating the external resistor at the ground reference of the ADC minimizes errors due to ground shift as discussed in the Advantages of Current-Output Architecture section. The MAX9934 is capable of both sourcing and sinking current from OUT, and thus can be used as a precision bidirectional current-sense amplifier. To enable this functionality, terminate ROUT to a midrail voltage VBIAS. ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934 ILOAD1 VCC = 3.3V VIN1 -0.1V VCM 5.5V RSENSE OUT1 MAX9934 MICROCONTROLLER CS CS1 ILOAD2 VCC = 3.3V VIN2 -0.1V VCM 5.5V RSENSE OUT2 MAX9934 CS CS2 ILOAD3 VCC = 3.3V VIN3 -0.1V VCM 5.5V RSENSE OUT3 MAX9934 CS3 CS TO EXTERNAL REFERENCE VOLTAGE R ROUT = R 2 VOUT VREF 10k ADC R 10k (OPTIONAL) Figure 5. Bidirectional Multiplexed Operation In Figure 5, VOUT is equal to VBIAS when the sum of all outputs is zero. For positive input-sense voltages, the MAX9934 sources current causing its output voltage to rise above VBIAS. For negative input-sense voltages, the MAX9934 sinks current causing its output voltage to be lower than VBIAS, thus allowing bidirectional current sensing. Since the ADC reference voltage, VREF, determines the full-scale reading, a common choice for V BIAS is VREF/2. The current output makes it possible to use a simple resistor-divider from VREF to GND to generate VBIAS. The output resistance for gain calculation is the parallel combination of the two resistors. For example, if two equal value resistors, R, are used to generate a VBIAS = VREF/2, the output termination resistance for gain calculation is ROUT = R/2. See Figure 5. ______________________________________________________________________________________ 13 MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing A MAX9934 can be deselected by either forcing VCS low as shown in Figures 4 and 5, or by making VCC = 0V as shown in Figure 6. In all these conditions, the MAX9934 maintains a high-impedance output with 0.1nA (typ) leakage current. In this state, OUT can rise above VCC if necessary. Thus, different supply voltages can be used to power different MAX9934 devices that are multiplexed on the same OUT bus. Multiplexing by forcing the MAX9934 to be powered down (VCC = 0V) reduces its supply current to zero to help extend battery life in portable applications. Choosing RSENSE and ROUT In the current-sense application, the monitored load current (I LOAD) develops a sense voltage (V SENSE) across a current-sense resistor (R SENSE ). The MAX9934 sources or sinks an output current that is proportional to VSENSE. Finally, the MAX9934 output current is provided to an output resistor (ROUT) to develop an output voltage across ROUT that is proportional to the sensed load current. VCC = 3.3V ILOAD1 VIN1 -0.1V VCM 5.5V 1/4 MAX4737 0.1F RSENSE CS OUT1 MAX9934 MICROCONTROLLER CS1 VCC = 3.3V 1/4 MAX4737 ILOAD2 VIN2 -0.1V VCM 5.5V 0.1F RSENSE CS OUT2 MAX9934 CS2 VCC = 3.3V 1/4 MAX4737 ILOAD3 VIN3 -0.1V VCM 5.5V 0.1F RSENSE CS OUT3 CS3 MAX9934 ADC ROUT 10k (OPTIONAL) Figure 6. Multiplexed Amplifiers with Power Saving 14 ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing When selecting RSENSE, consider the expected magnitude of I LOAD and the required V SENSE to manage power dissipation in RSENSE: RSENSE = VSENSE,MAX/ILOAD,MAX R SENSE is typically a low-value resistor specifically designed for current-sense applications. Finally, in selecting the appropriate MAX9934 gain option (GM), consider both the required VSENSE and IOUT: GM = IOUT,MAX/VSENSE,MAX Once all three component values have been selected in the current-sense application, the system performance is represented by: VSENSE = RSENSE x ILOAD and VOUT = VSENSE x GM x ROUT Accuracy In a first-order analysis of accuracy there are two MAX9934 specifications that contribute to output error, input offset (VOS) and gain error (GE). The MAX9934 has a maximum VOS of 10V and a maximum GE of 0.25%. Note that the tolerance and temperature coefficient of the chosen resistors directly affect the precision of any measurement system. Efficiency and Power Dissipation At high-current levels, the I2R losses in RSENSE can be significant. Take this into consideration when choosing the resistor value and its power dissipation (wattage) rating. Also, the sense resistor's value drifts if it is allowed to self-heat excessively. The precision VOS of the MAX9934 allows the use of a small sense resistor to reduce power dissipation and eliminate hot spots. Kelvin Contacts Due to the high currents that flow through RSENSE, take care to prevent trace resistance in the load current path from causing errors in the sense voltage. Use a four terminal current-sense resistor or Kelvin contacts (force and sense) PCB layout techniques. Table 1. Unidirectional Gain Table* PART MAX9934T MAX9934F OUTPUT CURRENT (A) ROUT (k) GAIN (V/V) 12.4 310 10 250 24.8 620 5 125 62 310 10 50 75 375 8 40 VSENSE (mV) *All calculations were made with VCC = 3.3V and VOUT(MAX) = VCC - VOH = 3.1V. Table 2. Bidirectional Gain Table* PART MAX9934T MAX9934F VSENSE (mV) OUTPUT CURRENT (A) ROUT (k) GAIN (V/V) 5.8 145 10 250 11.6 290 5 125 24 600 2.4 60 29 145 10 50 58 290 5 25 72 360 4 20 *All calculations were made with VCC = 3.3V, VOUT(MAX) = VCC VOH = 3.1V, VOUT(MIN) = VOL, and OUT connected to an external reference voltage of VREF = 1.65V through ROUT. Interfacing the MAX9934 to SAR ADCs Since the MAX9934 is essentially a high-output impedance current-source, its output termination resistor, ROUT, acts like a source impedance when driving an ADC channel. Most successive approximation register (SAR) architecture ADCs specify a maximum source resistance to avoid compromising the accuracy of their readings. Choose the output termination resistor ROUT such that it is less than that required by the ADC specification (10k or less). If the ROUT is larger than the source resistance specified, the ADC internal sampling capacitor can momentarily load the amplifier output and cause a drop in the voltage reading. If ROUT is larger than the source resistance specified, consider using a ceramic capacitor from ADC input to GND. This input capacitor supplies momentary charge to the internal ADC sampling capacitor, helping hold VOUT constant to within 1/2 LSB during the acquisition period. Use of this capacitor reduces the noise in the output signal to improve sensitivity of measurement. ______________________________________________________________________________________ 15 MAX9934 Three components are to be selected to optimize the current-sense system: R SENSE , R OUT , and the MAX9934 gain option (G M = 25A/mV or 5A/mV). Tables 1 and 2 are gain tables for unidirectional and bidirectional operation, respectively. They offer a few examples for both MAX9934 options having an output range of 3.1V unidirectional and 1.65V bidirectional. Note that the output current of the MAX9934 adds to its quiescent current. This can be calculated as follows: IOUT,MAX = VOUT,MAX/ROUT MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing Effect of Input-Bias Currents The MAX9934 has extremely low CMOS input-bias currents at both RS+ and RS- (0.1nA) when the input common-mode voltage is less than the supply voltage. When the input common-mode voltage becomes higher than the supply voltage, it draws the input stage operating current from RS-, 35A (typ). RS+ maintains its CMOS input characteristics. Low-input-bias currents are extremely useful in design of input filters for current-sense amplifiers. Input differential filters are sometimes required to average out rapidly varying load currents. An example of such load currents are those consumed by a processor, or switching power supply. Large bias and offset currents can interact with resistors used in these external filters to generate large input offset voltages and gain errors. For more detailed information, see Application Note AN3888: Performance of Current-Sense Amplifiers with Input Series Resistors. Due to the low-input-bias currents, resistors as large as 10k can be easily used without impact on error specifications with the MAX9934. For applications where the input common-mode voltage is below VCC, a balanced differential filter can be used. For applications where the input common-mode voltage extends above VCC, use a one-sided filter with a capacitor between RS+ and RS-, and a filter resistor in series with RS+ to maintain the excellent performance of the MAX9934. See Figure 7. PCB Layout For applications where the input common-mode voltage extends above VCC, trace resistance between RSENSE and RS- influences the effective VOS error due to the voltage drop developed across the trace resistance by the 35A input bias current at RS-. Monitoring Very Low Currents The accuracy of the MAX9934 leads to a wide dynamic range. This applies to both unidirectional mode and bidirectional mode. This is made possible in the unidirectional mode because the output maintains gain accuracy below 1mV as shown in the VOUT vs. VSENSE (VOUT < 5mV) graph in the Typical Operating Characteristics . Extending the useful output below 1mV makes it possible for the MAX9934 to accurately monitor very low currents. 16 BUCK CONTROLLER ASIC RS+ RS- MAX9934 Figure 7. One-Sided Input Filter Use as Precision Instrumentation Amplifier When the input common-mode voltage is below VCC, the input bias current of the RS- input drops to the 10pA range, the same range as the RS+ input. This low-input-bias current in combination with the rail-to-rail common-mode input range, the extremely high common-mode rejection, and low V OS of the MAX9934 make it ideally suited for use as a precision instrumentation amplifier. In addition, the MAX9934 is stable into an infinite capacitive load, allowing filtering flexibility. Figure 8 shows the MAX9934 in a multiplexed arrangement of strain-gauge amplifiers. UCSP Applications Information For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results go to the Maxim website at www.maxim-ic.com/ucsp for the Application Note 1891: Understanding the Basics of the Wafer-Level Chip-Scale Package (WL-CSP). ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing VIN1 MAX9934 VCC = 3.3V 0.1F OUT1 MAX9934 CS CS1 VCC = 3.3V 0.1F MICROCONTROLLER VIN2 OUT2 MAX9934 CS VCC = 3.3V VIN3 CS2 0.1F OUT3 MAX9934 CS TO EXTERNAL REFERENCE VOLTAGE R CS3 VREF 10k ROUT = R/2 ADC VOUT 10k R (OPTIONAL) Figure 8. Multiplexed, Strain-Gauge Amplifier Operation ______________________________________________________________________________________ 17 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing MAX9934 Pin Configurations TOP VIEW (BUMPS ON BOTTOM) TOP VIEW MAX9934T/F + + VCC 1 8 RS+ OUT 2 7 RS- 3 6 CS N.C. 4 5 N.C. MAX9934T/F GND RS+ B1 A1 VCC RS- B2 A2 OUT CS B3 A3 GND MAX UCSP Chip Information PROCESS: BiCMOS 18 ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing PACKAGE CODE DOCUMENT NO. 2x3 UCSP R61A1+1 21-0228 8 MAX U8+1 21-0036 UCSP.EPS PACKAGE TYPE ______________________________________________________________________________________ 19 MAX9934 Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. MAX9934 High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 20 ______________________________________________________________________________________ High-Precision, Low-Voltage, Current-Sense Amplifier with Current Output and Chip Select for Multiplexing REVISION NUMBER REVISION DATE 0 10/09 Initial release 1 1/10 Removed DFN package option 2 4/10 Removed future product references and updated lead temperature DESCRIPTION PAGES CHANGED -- 1-10, 18 1, 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21 (c) 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX9934 Revision History