19-4429; Rev 0; 3/09 KIT ATION EVALU E L B AVAILA Ultra-Precision, High-Side Current-Sense Amplifiers The MAX9922/MAX9923 ultra-precision, high-side current-sense amplifiers feature ultra-low offset voltage (VOS) of 25µV (max) and laser-trimmed gain accuracy better than 0.5%. The combination of low VOS and highgain accuracy allows precise current measurements even at very small sense voltages. The MAX9922/MAX9923 are capable of both unidirectional and bidirectional operation. For unidirectional operation, connect REF to GND. For bidirectional operation, connect REF to VDD/2. The MAX9922 has adjustable gain set with two external resistors. The MAX9923T/MAX9923H/MAX9923F use an internal laser-trimmed resistor for fixed gain of 25V/V, 100V/V, and 250V/V, respectively. The devices operate from a +2.85V to +5.5V single supply, independent of the input common-mode voltage, and draw only 700µA operating supply current and less than 1µA in shutdown. The +1.9V to +28V current-sense input common-mode voltage range makes the MAX9922/MAX9923 ideal for current monitoring in applications where high accuracy, large common-mode measurement range, and minimum full-scale VSENSE voltage is critical. The MAX9922/MAX9923 use a patented spread-spectrum autozeroing technique that constantly measures and cancels the input offset voltage, eliminating drift over time and temperature, and the effect of 1/f noise. This, in conjunction with the indirect current-feedback technique, achieves less than 25µV (max) offset voltage. The MAX9922/MAX9923 are available in a small 10-pin µMAX® package and are specified over the -40°C to +85°C extended temperature range. Applications Features ♦ Ultra-Precision VOS Over Temperature MAX9922: ±10µV (max) MAX9923T: ±25µV (max) MAX9923H: ±20µV (max) MAX9923F: ±10µV (max) ♦ ±0.5% (max) Full-Scale Gain Accuracy ♦ Bidirectional or Unidirectional ISENSE ♦ Multiple Gains Available Adjustable (MAX9922) +25V/V (MAX9923T) +100V/V (MAX9923H) +250V/V (MAX9923F) ♦ 1.9V to 28V Input Common-Mode Voltage, Independent of VDD ♦ Supply Voltage: +2.85V to +5.5V ♦ 700µA Supply Current, 1µA Shutdown Current ♦ Extended Temperature Range (-40°C to +85°C) ♦ Available in Space-Saving 10-Pin µMAX Ordering Information PINPACKAGE PART 10 µMAX MAX9922EUB+ TEMP RANGE GAIN (V/V) -40°C to +85°C Adjustable MAX9923TEUB+ 10 µMAX -40°C to +85°C 25 MAX9923HEUB+ 10 µMAX -40°C to +85°C 100 MAX9923FEUB+ 10 µMAX -40°C to +85°C 250 +Denotes a lead(Pb)-free/RoHS-compliant package. Notebook/Desktop Power Management Handheld Li+ Battery Current Monitoring Pin Configuration Precision Current Sources TOP VIEW RSB 1 RS+ Typical Operating Circuits appear at end of data sheet. µMAX is a registered trademark of Maxim Integrated Products, Inc. + 10 VDD 2 RS- 3 N.C. 4 GND 5 MAX9922 MAX9923T MAX9923H MAX9923F 9 OUT 8 FB 7 REF 6 SHDN µMAX ________________________________________________________________ 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 MAX9922/MAX9923 General Description MAX9922/MAX9923 Ultra-Precision, High-Side Current-Sense Amplifiers ABSOLUTE MAXIMUM RATINGS RSB, RS+, RS- to GND...........................................-0.3V to +30V VDD to GND ..............................................................-0.3V to +6V OUT, REF, FB, SHDN to GND .................-0.3V to the lower of (VDD + 0.3V) and +6V OUT Short Circuit to VDD or GND ..............................Continuous Differential Voltage (VRS+ - VRS-), (VRSB - VRS+), (VRSB - VRS-) ...................................................................±5.5V Current into Any Pin..........................................................±20mA Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 4.5mW/°C above +70°C) ...........362mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 (VRSB = VRS+ = VRS- = +12V, VDD = +3.3V, VGND = 0, VREF = VDD/2 for bidirectional, VREF = 0 for unidirectional, VSENSE = VRS+ - VRS- = 0, MAX9922 is set for AV =100V/V (R1 = 1kΩ, R2 = 99kΩ), SHDN = VDD, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX MAX9922 (AV = 100), VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.1 ±10 MAX9923T, VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.2 ±25 MAX9923H, VSENSE = 0, VREF = VDD/2 -40°C ≤ TA ≤ +85°C ±0.2 ±20 MAX9923F, VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.1 ±10 UNITS DC CHARACTERISTICS Input Offset Voltage (Notes 2, 3) Input Offset Voltage Temperature Drift (Notes 2, 4) VOS TCVOS µV MAX9922 (AV = 100V/V), VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.05 MAX9923T, VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.20 MAX9923H, VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.10 MAX9923F, VSENSE = 0, VREF = VDD/2, -40°C ≤ TA ≤ +85°C ±0.05 µV/°C Input Common-Mode Range VCMR Guaranteed by CMRR 1.90 Input Common-Mode Rejection CMRR 1.9V ≤ VRS+ ≤ 28V, -40°C ≤ TA ≤ +85°C (Note 2) 121 MAX9922 Gain 2 AV 28.00 140 V dB Adj MAX9923T 25 MAX9923H 100 MAX9923F 250 _______________________________________________________________________________________ V/V Ultra-Precision, High-Side Current-Sense Amplifiers (VRSB = VRS+ = VRS- = +12V, VDD = +3.3V, VGND = 0, VREF = VDD/2 for bidirectional, VREF = 0 for unidirectional, VSENSE = VRS+ - VRS- = 0, MAX9922 is set for AV =100V/V (R1 = 1kΩ, R2 = 99kΩ), SHDN = VDD, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MAX9922 (AV = 100) MAX9923T Gain Accuracy (Note 5) ΔAV Gain Nonlinearity ~AV Open-Loop Gain AVOL Input Bias Current MIN TA = +25°C TYP MAX ±0.17 ±0.40 ±0.12 ±0.30 ±0.24 ±0.40 -40°C ≤ TA ≤ +85°C ±0.60 TA = +25°C -40°C ≤ TA ≤ +85°C ±0.60 TA = +25°C MAX9923H -40°C ≤ TA ≤ +85°C MAX9923F -40°C ≤ TA ≤ +85°C UNITS % ±0.75 TA = +25°C ±0.21 ±0.50 ±0.80 MAX9922 (AV = 100) ±0.06 MAX9923T ±0.04 MAX9923H ±0.06 MAX9923F MAX9922 ±0.12 IRS+, IRS- % 160 dB 1 pA FB Bias Current IFB MAX9922 1 pA FB Resistance RFB MAX9923T/MAX9923H/MAX9923F resistance between FB and REF 1 kΩ Guaranteed by REF CMRR test REF Input Range REF Common-Mode Rejection Ratio VDD 1.4 -40°C ≤ TA ≤ +85°C 0 VDD 1.6 VOH 100 ±16 ±20 ±60 ±70 MAX9923H (bidirectional), VSENSE ≥ ±20mV ±16 ±20 MAX9923F (bidirectional), VSENSE ≥ ±4mV ±6 ±7 7 30 VOH = VDD – VOUT (Note 7) RL = 10kΩ to GND and REF = GND 1 6 1 10 RL = 10kΩ to VDD and REF = VDD - 1.4 6 30 VIL VDD = 5.5V SHDN Logic-High VIH VDD = 5.5V µA mV RL = 10kΩ to VDD and REF = VDD - 1.4 RL = 10kΩ to GND and REF = GND SHDN Logic-Low V dB MAX9923T (bidirectional), VSENSE ≥ ±100mV VOL IIH/IIL 94 MAX9922 (bidirectional), VSENSE ≥ ±20mV OUT Low Voltage (Note 7) SHDN Input Current 0 0 ≤ REF ≤ VDD - 1.4V (Note 2) REF Input Current (Note 6) OUT High Voltage TA = +25°C 0.3 0.6 x VDD mV V V 0.001 ±1 µA _______________________________________________________________________________________ 3 MAX9922/MAX9923 ELECTRICAL CHARACTERISTICS (continued) MAX9922/MAX9923 Ultra-Precision, High-Side Current-Sense Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VRSB = VRS+ = VRS- = +12V, VDD = +3.3V, VGND = 0, VREF = VDD/2 for bidirectional, VREF = 0 for unidirectional, VSENSE = VRS+ - VRS- = 0, MAX9922 is set for AV =100V/V (R1 = 1kΩ, R2 = 99kΩ), SHDN = VDD, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS AC CHARACTERISTICS -3dB Small-Signal Bandwidth BW VSENSE = 10mVP-P VSENSE = 5mVP-P Slew Rate SR OUT Settling Time to 1% of Final Value Autozeroing Clock Frequency 10 MAX9923T 50 MAX9923H 10 2.5 MAX9923F ΔVOUT = 2V, CLOAD = 100pF CLOAD = 7pF Input-Voltage Noise Peak-to-Peak MAX9922 0.4 MAX9922 200 MAX9923T 100 MAX9923H 200 MAX9923F 400 fO = 0.1Hz to 10Hz fC Capacitive-Load Stability kHz V/µs µs 3.4 µVP-P Pseudo-random 20 kHz No sustained oscillations 200 pF POWER-SUPPLY CHARACTERISTICS Supply Voltage Range Power-Supply Rejection Ratio Quiescent Supply Current VDD PSRR IDD Power-Down Input Current 4 2.85V ≤ VDD ≤ 5.5V, -40°C ≤ TA ≤ +85°C (Note 2) 2.85 93 5.50 99 VDD = 5.0V 780 1300 VDD = 3.0V 700 1500 VRSB = 12V 200 300 V SHDN = 0.3V 0.05 1 IRSB_SD V SHDN = 0.3V, VRSB = 28V 0.05 1 VDD = VREF = 0, VRSB = VRS+ = VRS- = 28V 0.01 0.1 IRS+L, IRS-L _______________________________________________________________________________________ V dB IDD_SD IRSB Shutdown Supply Current Guaranteed by PSRR µA µA µA Ultra-Precision, High-Side Current-Sense Amplifiers (VRSB = VRS+ = VRS- = +12V, VDD = +3.3V, VGND = 0, VREF = VDD/2 for bidirectional, VREF = 0 for unidirectional, VSENSE = VRS+ - VRS- = 0, MAX9922 is set for AV =100V/V (R1 = 1kΩ, R2 = 99kΩ), SHDN = VDD, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER Power-Down Supply Current Power-Up Time Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: SYMBOL IRSBL TYP MAX UNITS VDD = VREF = 0, VRSB = VRS+ = VRS- = 28V CONDITIONS MIN 0.05 1 µA MAX9922, AV = 100V/V, VREF = 0, VSENSE = 10mV, VDD = 0 to 3.3V, settling to 0.1% of final value 800 µs All devices are 100% production tested at TA = +85°C. All temperature limits are guaranteed by design. VOS is measured in bidirectional mode with VREF = VDD/2. Data sheet limits are guaranteed by design and bench characterization. Thermocouple effects preclude measurement of this parameter during production testing. Devices are screened during production testing to eliminate defective units. VOS drift limits are guaranteed by design and bench characterization and are the average of drift from -40°C to +25°C and from +25°C to +85°C. VRSB = VRS+ = 12V, VREF = VDD/2 for bipolar mode and VREF = 0 for unipolar mode. Gain accuracy and gain linearity are specified over a VSENSE range that keeps the output voltage 250mV away from the rails to achieve full accuracy. Output of the part is rail-to-rail, and goes to within 25mV of the rails, but accuracy is not maintained. Linear operation is not guaranteed for VSENSE voltages > ±150mV. See the Typical Operating Characteristics section for plots of Input vs. Output. This is the worst-case REF current needed to directly drive the bottom terminal of the gain setting resistors, at VDD = 3.3V, and VREF = VDD/2. An internal 1kΩ resistor (R1) is present in the MAX9923T/MAX9923H/MAX9923F between the FB and REF pins, while in the MAX9922 the resistor is external and user selectable. A voltage identical to the VSENSE develops across this resistor. In all versions the REF input current is dependent on the magnitude and polarity of VSENSE, and in the MAX9922 it is dependent on the value of the external resistor as well. See the External Reference section for more details. The range of VREF, VCM, and VSENSE may limit the output swing of the MAX9922 with adjustable gain set to less than 100V/V. _______________________________________________________________________________________ 5 MAX9922/MAX9923 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25°C, unless otherwise noted.) 80 70 50 60 60 MAX9922/23 toc02 60 MAX9922/23 toc01 90 50 40 40 30 N (%) 40 50 N (%) N (%) MAX9922 OFFSET VOLTAGE DRIFT HISTOGRAM MAX9922 INPUT OFFSET VOLTAGE HISTOGRAM MAX9922/23 toc03 MAX9922 UNIPOLAR GAIN ACCURACY HISTOGRAM 30 30 20 20 10 10 20 10 0 0 0 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -10 -8 -6 -4 -2 0 2 4 6 8 -50 -40 -30 -20 -10 0 10 VOS (μV) TCVOS (nV/°C) INPUT REFERRED OFFSET vs. INPUT COMMON-MODE VOLTAGE MAX9922 INPUT vs. OUTPUT MAX9922 INPUT vs. OUTPUT 2 0 -2 0 -0.5 0.5 0 -0.5 -1.0 -1.0 -6 -1.5 -1.5 -2.0 -2.0 4 8 12 16 20 28 24 -250 -150 INPUT COMMON MODE (V) -50 0 50 -15 -25 250 150 VOH/VOL vs. IOH/IOL REF = GND 0.4 MAX9922/23 toc08 1.0 MAX9922/23 toc07 0.5 -5 0.9 0.8 VOH/VOL (V) 0.7 0.3 0.2 0.6 0.5 0.4 0.3 0.1 VOH 0.2 0.1 0 5 10 15 INPUT COMMON MODE (V) 6 VOL 0 0 20 25 0 0 5 DIFFERENTIAL INPUT (mV) DIFFERENTIAL INPUT (mV) GAIN ERROR vs. INPUT COMMON-MODE VOLTAGE GAIN ERROR (%) MAX9922/23 toc06 1.0 0.5 -4 -8 RF = 100kΩ RG = 1kΩ 1.5 OUTPUT-REF (V) 1.0 OUTPUT-REF (V) 4 RF = 100kΩ RG = 20kΩ 1.5 2.0 MAX9922/23 toc05 2.0 MAX9922/23 toc04 6 0 10 20 30 40 50 GAIN ACCURACY (%) 8 OFFSET VOLTAGE (μV) MAX9922/MAX9923 Ultra-Precision, High-Side Current-Sense Amplifiers 2 4 6 8 10 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 15 25 Ultra-Precision, High-Side Current-Sense Amplifiers SUPPLY CURRENT vs. TEMPERATURE RSB CURRENT vs. TEMPERATURE 0.9 VDD = 5.5V VDD = 3.3V 0.8 0.7 VDD = 2.85V 0.6 MAX9922/23 toc10 1.0 SUPPLY CURRENT (mA) 1.1 SUPPLY CURRENT (mA) 0.4 MAX9922/23 toc09 1.2 0.3 VRSB = 28V VRSB = 12V 0.2 VRSB = 1.9V 0.1 0.5 0.4 0 -15 10 35 60 -40 -15 35 60 TEMPERATURE (°C) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE MAX9922 GAIN vs. FREQUENCY 140 MAX9922/23 toc11 25 120 GAIN = OPEN LOOP 85 100 GAIN (dB) 20 VDD = 2.85V 15 VDD = 5.5V 10 80 60 GAIN = 1000 40 VDD = 3.3V 5 20 0 -40 -15 10 35 60 0 10E-3 1E+0 100E+0 10E+3 1E+6 100E-3 10E+0 1E+3 100E+3 FREQUENCY (Hz) 85 TEMPERATURE (°C) PSRR vs. FREQUENCY INPUT CMRR vs. FREQUENCY -70 -80 -70 -80 PSRR (dB) -90 -100 MAX9922/23 toc14 -60 MAX9922/23 toc13 -60 CMRR (dB) 10 TEMPERATURE (°C) 30 SUPPLY CURRENT (nA) 85 MAX9922/23 toc12 -40 -90 -100 -110 -110 -120 -120 -130 -130 -140 -140 1E+0 10E+0 100E+0 1E+3 FREQUENCY (Hz) 10E+3 100E+3 1E+0 10E+0 100E+0 1E+3 10E+3 100E+3 FREQUENCY (Hz) _______________________________________________________________________________________ 7 MAX9922/MAX9923 Typical Operating Characteristics (continued) (VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25°C, unless otherwise noted.) PEAK-TO-PEAK NOISE (0.1Hz TO 10Hz) INPUT NOISE DENSITY vs. FREQUENCY MAX9922/23 toc16 MAX9922/23 toc15 250 NOISE DENSITY (nV/√Hz) 200 150 1.25μV/div 100 50 32kHz SPIKE ENERGY = 4.3μVRMS 0 10 100 1,000 10,000 1s/div 100,000 FREQUENCY (Hz) POWER-ON RESPONSE (MAX9922, AV = 100) MAX9922/23 toc18 LARGE SIGNAL INPUT STEP RESPONSE (MAX9922, AV = 100) MAX9922/23 toc17 INPUT (10mV/div) 0V OUT (500mV/div) 0V OUTPUT (1V/div) 0V VDD (1V/div) VSENSE = 10mV TIME (200μs/div) TIME (80μs/div) SHUTDOWN ON/OFF TRANSIENT (MAX9922, AV = 100) MAX9922/23 toc19 MAX9922/MAX9923 Ultra-Precision, High-Side Current-Sense Amplifiers SHDN (1V/div) 0V OUTPUT (500mV/div) 0V VSENSE = 10mV TIME (200μs/div) 8 _______________________________________________________________________________________ 0V Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/23 toc20 INPUT (100mV/div) MAX9922/23 toc21 OVERLOAD RECOVERY (OUTPUT LIMITING) (MAX9922, AV = 100) SATURATION/OVERLOAD RECOVERY (INPUT LIMITED) (MAX9922) INPUT (50mV/div) 0V 0V OUTPUT (1V/div) OUTPUT (1V/div) 0V 0V GAIN = 5V/V TIME (150μs/div) TIME (200μs/div) Pin Description PIN NAME FUNCTION 1 RSB Current-Sense Amplifier Input Stage Supply. Connect to either RS+ or RS-. 2 RS+ Current-Sense Amplifier Positive Input 3 RS- Current-Sense Amplifier Negative Input 4 N.C. No Connection. Not internally connected. 5 GND Ground 6 SHDN Shutdown Logic Input. Connect to GND to reduce quiescent current to 1µA. Connect to VDD for normal operation. 7 REF Reference Voltage Input. Connect to an external voltage to provide a bidirectional current-sense output. Connect to GND for unidirectional operation. Gain-Set Feedback Input. Connect an optional noise reduction capacitor between OUT and FB. 8 FB MAX9922: Adjustable Gain. Connect a resistive-divider feedback network between OUT, FB, and REF to set the current-sense amplifier gain. Use an external combination of R1 and R2 resistors for gain = 1 + (R2/R1). MAX9923T/MAX9923H/MAX9923F: Fixed gain. See the Functional Diagrams. 9 OUT Voltage Output. VOUT is proportional to VSENSE. 10 VDD Power-Supply Voltage Input. Bypass to GND with a 0.1µF capacitor. _______________________________________________________________________________________ 9 MAX9922/MAX9923 Typical Operating Characteristics (continued) (VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25°C, unless otherwise noted.) Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923 Functional Diagrams RSB RS+ 1 10 2 9 3 8 4 7 VDD RSB OUT RS+ 1 10 2 9 R2 RS- FB GND 5 MAX9922 GAIN = 1 + 6 REF SHDN RS- 8 N.C. GND 7 MAX9923 5 R2 The MAX9922/MAX9923 monitor current through a current-sense resistor and amplify the voltage across the resistor. The 28V input common-mode voltage (VRS+) range of the MAX9922/MAX9923 is independent of the supply voltage (V DD ). High-side current monitoring does not interfere with the ground path of the load being measured, making the MAX9922/MAX9923 particularly useful in a wide range of high-voltage systems. 10 6 REF SHDN MAX9923 VERSION The MAX9922/MAX9923 high-side, current-sense amplifiers implement a patented spread-spectrum autozeroing technique that minimizes the input offset error, offset drift over time and temperature, and the effect of 1/f noise. This technique achieves less than 25µV (max) offset voltage. The MAX9922/MAX9923 high-side current-sense amplifiers feature a +1.9V to +28V input common-mode range that is independent of supply voltage (VDD). This feature allows the monitoring of current out of a battery as low as +1.9V and enables high-side current sensing at voltages greater than the supply voltage. FB R1 4 ( R1 ) Detailed Description OUT R2 3 R1 N.C. VDD GAIN T 25 H 100 F 250 The MAX9922/MAX9923 use Maxim’s patented indirect current feedback achitecture. This architecture converts the differential input voltage signal to a current through an input transconductance stage. An output transconductance stage converts a portion of the output voltage (equal to the output voltage divided by the gain) into another precision current. These two currents are subtracted and the result is fed to a loop amplifier with sufficient gain to minimize errors (see the Functional Diagrams.) Battery-powered systems require a precise bidirectional current-sense amplifier to accurately monitor the battery’s charge and discharge currents. Measurements of OUT with respect to VREF yield a positive and negative voltage during charge and discharge cycles (Figure 1). The MAX9922 allows adjustable gain with a pair of external resistors between OUT, FB, and REF. The MAX9923T/ MAX9923H/MAX9923F use laser-trimmed internal resistors for fixed gains of 25, 100, and 250, respectively, with 0.5% gain accuracy (see the Functional Diagrams.) ______________________________________________________________________________________ Ultra-Precision, High-Side Current-Sense Amplifiers 5V VOUT - VREF AV = 100 2.5V CHARGE CURRENT -25mV 0 25mV DISCHARGE CURRENT -2.5V ( VOUT = RSENSE x 1 + R2 x ISENSE + VREF R1 ) Figure 1. Bidirectional Current-Sense Transfer Function Shutdown The MAX9922/MAX9923 feature a logic shutdown input to reduce the supply current to less than 1µA. Drive SHDN high for normal operation. Drive SHDN low to place the device in shutdown mode. In shutdown mode, the current drawn from both the VDD input and the current-sense amplifier inputs (RSB, RS+, and RS-) is less than 1µA each. External Reference The MAX9922/MAX9923 are capable of both unidirectional and bidirectional operation. For unidirectional current-sense applications, connect the REF input to GND. For bidirectional, connect REF to a reference. This sets bidirectional current sense with VOUT = VREF for V SENSE = 0mV. Positive V SENSE causes OUT to swing toward the positive supply, while negative VSENSE causes OUT to swing toward GND. This feature allows the output voltage to measure both charge and discharge currents. Use VREF = VDD/2 for maximum dynamic range. Input Differential Signal Range The MAX9922/MAX9923 feature a proprietary input structure optimized for small differential signals as low as 10mV full scale for high efficiency with lowest power dissipation in the sense resistor, or +100mV full scale for high dynamic range. The output of the MAX9922/ MAX9923 allows for bipolar input differential signals. Gain accuracy is specified over the VSENSE range to keep the output voltage 250mV away from the rails to achieve full accuracy. Output of the part is rail-to-rail and goes to within 25mV of the rails, but accuracy is not maintained. Linear operation is not guaranteed for input sense voltages greater than ±150mV. Applications Information Power Supply, Bypassing, and Layout Good layout technique optimizes performance by decreasing the amount of stray capacitance at the high-side, current-sense amplifier gain-setting pins, FB to REF and FB to GND. Capacitive decoupling between V DD to GND of 0.1µF is recommended. Since the MAX9922/MAX9923 feature ultra-low input offset voltage, board leakage and thermocouple effects can easily introduce errors in the input offset voltage readings when used with high-impedance signal sources. Minimize board leakage current and thermocouple effects by thoroughly cleaning the board and placing the matching components very close to each other and with appropriate orientation. For noisy digital environments, the use of a multilayer printed circuit board (PCB) with separate ground and power-supply planes is recommended. Keep digital signals far away from the sensitive analog inputs. Unshielded long traces at the input and feedback terminals of the amplifier can degrade performance due to noise pick-up. ______________________________________________________________________________________ 11 MAX9922/MAX9923 In bidirectional operation, the external voltage applied to VREF has to be able to supply the current in the feedback network between OUT, FB, and REF. This current is simply the input sense voltage divided by the resistance between FB and REF (1kΩ typical for MAX9923). Furthermore, ensure the external voltage source supplied to REF has a low source resistance to prevent gain errors (e.g., use a stand-alone reference voltage or an op amp to buffer a high-value resistor string.) See the Typical Operating Circuits. MAX9922/MAX9923 Ultra-Precision, High-Side Current-Sense Amplifiers Optional Noise Reduction Capacitor Sense Resistor Connections A noise reduction capacitance of ~1nF can be connected between OUT and FB, if needed. Noise reduction is achieved by both limiting the amplifier bandwidth, reducing contribution of broadband white noise and by attenuating contribution of any small 20kHz autozero ripple that appears at the output. Using higher values of feedback capacitance reduces the output noise of the amplifier, but also reduces its signal bandwidth. Take care to prevent solder and trace resistance from causing errors in the sensed voltage because of the high currents that flow through RSENSE. Either use a four terminal current-sense resistor or use Kelvin (force and sense) PCB layout techniques to minimize these errors. 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. The sense resistor’s value will drift if it is allowed to heat up excessively. The precision V OS of the MAX9922/MAX9923 allows the use of small sense resistors to reduce power dissipation and reduce hot spots. 12 ______________________________________________________________________________________ Ultra-Precision, High-Side Current-Sense Amplifiers Unidirectional Mode VSENSE BATT 1.9V TO 28V 3.3V RSB RS+ RLOAD RS- VDD 12-BIT ADC OUT MAX9923T MAX9923H MAX9923F ON SHDN 1nF* FB REF GND OFF *OPTIONAL NOISE REDUCTION Bidirectional Mode VSENSE TO WALL-CUBE/CHARGER BATT 1.9V TO 28V 3.3V RSB RS+ RLOAD RS- VDD 12-BIT ADC VREF = 2.5V OUT ON MAX9923T MAX9923H MAX9923F SHDN GND 1nF* FB REF 1.25V OFF *OPTIONAL NOISE REDUCTION Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 13 MAX9922/MAX9923 Typical Operating Circuits Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE CODE DOCUMENT NO. 10 µMAX U10-2 21-0061 10LUMAX.EPS PACKAGE TYPE α α