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19-4429; Rev 0; 3/09
KIT ATION EVALU BLE AVAILA
Ultra-Precision, High-Side Current-Sense Amplifiers
Features
Ultra-Precision VOS Over Temperature MAX9922: 10V (max) MAX9923T: 25V (max) MAX9923H: 20V (max) MAX9923F: 10V (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 700A Supply Current, 1A Shutdown Current Extended Temperature Range (-40C to +85C) Available in Space-Saving 10-Pin MAX
General Description
The MAX9922/MAX9923 ultra-precision, high-side current-sense amplifiers feature ultra-low offset voltage (VOS) of 25V (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 700A operating supply current and less than 1A 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 25V (max) offset voltage. The MAX9922/MAX9923 are available in a small 10-pin MAX(R) package and are specified over the -40C to +85C extended temperature range.
MAX9922/MAX9923
Ordering Information
PART MAX9922EUB+ MAX9923TEUB+ MAX9923HEUB+ MAX9923FEUB+ PINPACKAGE 10 MAX 10 MAX 10 MAX 10 MAX TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C GAIN (V/V) Adjustable 25 100 250
Applications
Notebook/Desktop Power Management Handheld Li+ Battery Current Monitoring Precision Current Sources
+Denotes a lead(Pb)-free/RoHS-compliant package.
Pin Configuration
TOP VIEW
RSB 1 RS+ 2 3 4 5 + 10 VDD 9 OUT FB REF SHDN
Typical Operating Circuits appear at end of data sheet. MAX is a registered trademark of Maxim Integrated Products, Inc.
RSN.C. GND
MAX9922 MAX9923T MAX9923H MAX9923F
8 7 6
MAX
________________________________________________________________ Maxim Integrated Products
1
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.
Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
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 = +70C) 10-Pin MAX (derate 4.5mW/C above +70C) ...........362mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 1k, R2 = 99k), SHDN = VDD, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER DC CHARACTERISTICS MAX9922 (AV = 100), VSENSE = 0, VREF = VDD/2, -40C TA +85C Input Offset Voltage (Notes 2, 3) MAX9923T, VSENSE = 0, VREF = VDD/2, -40C TA +85C VOS MAX9923H, VSENSE = 0, VREF = VDD/2 -40C TA +85C MAX9923F, VSENSE = 0, VREF = VDD/2, -40C TA +85C MAX9922 (AV = 100V/V), VSENSE = 0, VREF = VDD/2, -40C TA +85C MAX9923T, VSENSE = 0, VREF = VDD/2, -40C TA +85C MAX9923H, VSENSE = 0, VREF = VDD/2, -40C TA +85C MAX9923F, VSENSE = 0, VREF = VDD/2, -40C TA +85C Input Common-Mode Range Input Common-Mode Rejection VCMR CMRR Guaranteed by CMRR 1.9V VRS+ 28V, -40C TA +85C (Note 2) MAX9922 Gain AV MAX9923T MAX9923H MAX9923F 1.90 121 140 Adj 25 100 250 V/V 0.1 0.2 0.2 0.1 10 25 V 20 10 SYMBOL CONDITIONS MIN TYP MAX UNITS
0.05
Input Offset Voltage Temperature Drift (Notes 2, 4)
0.20 V/C 0.10 0.05 28.00 V dB
TCVOS
2
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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 = 1k, R2 = 99k), SHDN = VDD, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SYMBOL MAX9922 (AV = 100) Gain Accuracy (Note 5) MAX9923T AV MAX9923H MAX9923F MAX9922 (AV = 100) Gain Nonlinearity ~AV MAX9923T MAX9923H MAX9923F MAX9922 MAX9922 MAX9923T/MAX9923H/MAX9923F resistance between FB and REF Guaranteed by REF CMRR test TA = +25C -40C TA +85C 0 0 94 100 16 60 16 6 7 1 1 6 0.6 x VDD 0.001 1 20 70 20 7 30 mV RL = 10k to VDD and REF = VDD - 1.4 6 10 30 0.3 mV V V A A CONDITIONS TA = +25C -40C TA +85C TA = +25C -40C TA +85C TA = +25C -40C TA +85C TA = +25C -40C TA +85C 0.06 0.04 0.06 0.12 160 1 1 1 VDD 1.4 VDD 1.6 V dB pA pA k % 0.21 0.24 0.12 MIN TYP 0.17 MAX 0.40 0.60 0.30 0.60 0.40 0.75 0.50 0.80 % UNITS
MAX9922/MAX9923
Open-Loop Gain Input Bias Current FB Bias Current FB Resistance
AVOL IRS+, IRSIFB RFB
REF Input Range
REF Common-Mode Rejection Ratio
0 REF VDD - 1.4V (Note 2) MAX9922 (bidirectional), VSENSE 20mV
dB
REF Input Current (Note 6)
MAX9923T (bidirectional), VSENSE 100mV MAX9923H (bidirectional), VSENSE 20mV MAX9923F (bidirectional), VSENSE 4mV VOH = VDD - VOUT (Note 7) RL = 10k to GND and REF = GND
OUT High Voltage
VOH
OUT Low Voltage (Note 7) SHDN Logic-Low SHDN Logic-High SHDN Input Current
VOL VIL VIH IIH/IIL
RL = 10k to GND and REF = GND RL = 10k to VDD and REF = VDD - 1.4 VDD = 5.5V VDD = 5.5V
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
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 = 1k, R2 = 99k), SHDN = VDD, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER AC CHARACTERISTICS MAX9922 -3dB Small-Signal Bandwidth BW VSENSE = 10mVP-P VSENSE = 5mVP-P Slew Rate OUT Settling Time to 1% of Final Value Input-Voltage Noise Peak-to-Peak Autozeroing Clock Frequency Capacitive-Load Stability POWER-SUPPLY CHARACTERISTICS Supply Voltage Range Power-Supply Rejection Ratio VDD PSRR IDD IRSB Shutdown Supply Current Power-Down Input Current IDD_SD IRSB_SD IRS+L, IRS-L Guaranteed by PSRR 2.85V VDD 5.5V, -40C TA +85C (Note 2) VDD = 5.0V VDD = 3.0V VRSB = 12V V SHDN = 0.3V V SHDN = 0.3V, VRSB = 28V VDD = VREF = 0, VRSB = VRS+ = VRS- = 28V 2.85 93 99 780 700 200 0.05 0.05 0.01 1300 1500 300 1 1 0.1 A A A 5.50 V dB fC SR MAX9923T MAX9923H MAX9923F MAX9922 CLOAD = 7pF MAX9923T MAX9923H MAX9923F fO = 0.1Hz to 10Hz Pseudo-random No sustained oscillations VOUT = 2V, CLOAD = 100pF 10 50 10 2.5 0.4 200 100 200 400 3.4 20 200 VP-P kHz pF s V/s kHz SYMBOL CONDITIONS MIN TYP MAX UNITS
Quiescent Supply Current
4
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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 = 1k, R2 = 99k), SHDN = VDD, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Power-Down Supply Current Power-Up Time SYMBOL IRSBL CONDITIONS VDD = VREF = 0, VRSB = VRS+ = VRS- = 28V MAX9922, AV = 100V/V, VREF = 0, VSENSE = 10mV, VDD = 0 to 3.3V, settling to 0.1% of final value MIN TYP 0.05 800 MAX 1 UNITS A s
MAX9922/MAX9923
Note 1: Note 2: Note 3: Note 4: Note 5:
Note 6:
Note 7:
All devices are 100% production tested at TA = +85C. 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 -40C to +25C and from +25C to +85C. 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 1k 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.
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Typical Operating Characteristics
(VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25C, unless otherwise noted.)
MAX9922 UNIPOLAR GAIN ACCURACY HISTOGRAM
MAX9922/23 toc01
MAX9922 INPUT OFFSET VOLTAGE HISTOGRAM
MAX9922/23 toc02
MAX9922 OFFSET VOLTAGE DRIFT HISTOGRAM
MAX9922/23 toc03
90 80 70 60 N (%)
60 50 40 N (%)
60 50 40 N (%) 30 20 10 0
50 40 30 20 10 0 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 GAIN ACCURACY (%)
30 20 10 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 VOS (V)
-50 -40 -30 -20 -10 0
10 20 30 40 50
TCVOS (nV/C)
INPUT REFERRED OFFSET vs. INPUT COMMON-MODE VOLTAGE
MAX9922/23 toc04
MAX9922 INPUT vs. OUTPUT
MAX9922/23 toc05
MAX9922 INPUT vs. OUTPUT
1.5 1.0 OUTPUT-REF (V) 0.5 0 -0.5 -1.0 -1.5 -2.0 RF = 100k RG = 1k
MAX9922/23 toc06
8 6 OFFSET VOLTAGE (V) 4 2 0 -2 -4 -6 -8 0 4 8 12 16 20 24
2.0 1.5 1.0 OUTPUT-REF (V) 0.5 0 -0.5 -1.0 -1.5 -2.0 RF = 100k RG = 20k
2.0
28
-250
-150
-50 0
50
150
250
-25
-15
-5
0
5
15
25
INPUT COMMON MODE (V)
DIFFERENTIAL INPUT (mV)
DIFFERENTIAL INPUT (mV)
GAIN ERROR vs. INPUT COMMON-MODE VOLTAGE
MAX9922/23 toc07
VOH/VOL vs. IOH/IOL
0.9 0.8 0.7 VOH/VOL (V)
MAX9922/23 toc08
0.5 REF = GND 0.4 GAIN ERROR (%)
1.0
0.3
0.6 0.5 0.4 0.3 VOH VOL 0 2 4 6 8 10
0.2
0.1
0.2 0.1
0 0 5 10 15 20 25 INPUT COMMON MODE (V)
0 OUTPUT CURRENT (mA)
6
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Ultra-Precision, High-Side Current-Sense Amplifiers
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX9922/23 toc09
MAX9922/MAX9923
RSB CURRENT vs. TEMPERATURE
MAX9922/23 toc10
1.2 1.1 SUPPLY CURRENT (mA) 1.0 0.9 0.8 0.7 VDD = 2.85V 0.6 0.5 0.4 -40 -15 10 35 60 VDD = 3.3V VDD = 5.5V
0.4
SUPPLY CURRENT (mA)
0.3 VRSB = 12V 0.2 VRSB = 1.9V 0.1 VRSB = 28V
0 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX9922/23 toc11
MAX9922 GAIN vs. FREQUENCY
MAX9922/23 toc12
30 25 SUPPLY CURRENT (nA) 20
140 120 GAIN = OPEN LOOP 100 GAIN (dB) 80 60 40 20 GAIN = 1000
15 VDD = 5.5V 10 VDD = 3.3V 5 0 -40 -15 10
VDD = 2.85V
35
60
85
TEMPERATURE (C)
0 10E-3 1E+0 100E+0 10E+3 1E+6 100E-3 10E+0 1E+3 100E+3 FREQUENCY (Hz)
INPUT CMRR vs. FREQUENCY
MAX9922/23 toc13
PSRR vs. FREQUENCY
-70 -80 PSRR (dB) -90 -100 -110 -120 -130 -140
MAX9922/23 toc14
-60 -70 -80 CMRR (dB) -90 -100 -110 -120 -130 -140 1E+0 10E+0 100E+0 1E+3 10E+3
-60
100E+3
1E+0
10E+0
100E+0
1E+3
10E+3
100E+3
FREQUENCY (Hz)
FREQUENCY (Hz)
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25C, unless otherwise noted.)
INPUT NOISE DENSITY vs. FREQUENCY
MAX9922/23 toc15
PEAK-TO-PEAK NOISE (0.1Hz TO 10Hz)
MAX9922/23 toc16
250
NOISE DENSITY (nV/Hz)
200
150 1.25V/div 100
50 32kHz SPIKE ENERGY = 4.3VRMS 0 10 100 1,000 FREQUENCY (Hz) 10,000 100,000 1s/div
LARGE SIGNAL INPUT STEP RESPONSE (MAX9922, AV = 100)
MAX9922/23 toc17
POWER-ON RESPONSE (MAX9922, AV = 100)
MAX9922/23 toc18
INPUT (10mV/div)
0V
OUT (500mV/div) 0V
OUTPUT (1V/div) 0V
VDD (1V/div) VSENSE = 10mV 0V
TIME (200s/div)
TIME (80s/div)
SHUTDOWN ON/OFF TRANSIENT (MAX9922, AV = 100)
MAX9922/23 toc19
SHDN (1V/div)
0V
OUTPUT (500mV/div) 0V VSENSE = 10mV TIME (200s/div)
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSHDN = VDD, VRSB = VRS+ = VRS- = 12V, TA = +25C, unless otherwise noted.)
SATURATION/OVERLOAD RECOVERY (INPUT LIMITED) (MAX9922)
MAX9922/23 toc20
OVERLOAD RECOVERY (OUTPUT LIMITING) (MAX9922, AV = 100)
MAX9922/23 toc21
INPUT (100mV/div)
INPUT (50mV/div)
0V 0V
OUTPUT (1V/div) 0V GAIN = 5V/V TIME (200s/div)
OUTPUT (1V/div) 0V
TIME (150s/div)
Pin Description
PIN 1 2 3 4 5 6 7 NAME RSB RS+ RSN.C. GND SHDN REF Current-Sense Amplifier Positive Input Current-Sense Amplifier Negative Input No Connection. Not internally connected. Ground Shutdown Logic Input. Connect to GND to reduce quiescent current to 1A. Connect to VDD for normal operation. 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 10 OUT VDD Voltage Output. VOUT is proportional to VSENSE. Power-Supply Voltage Input. Bypass to GND with a 0.1F capacitor. FUNCTION Current-Sense Amplifier Input Stage Supply. Connect to either RS+ or RS-.
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Functional Diagrams
RSB
1
10
VDD
RSB
1
10
VDD
RS+
2
9
OUT R2
RS+
2 R2
9
OUT
RS-
3
8
FB R1
RS-
3 R1
8
FB
N.C.
4
7
REF
N.C.
4
7
REF
GND
5
MAX9922
6
SHDN
GND
5
MAX9923
6
SHDN
GAIN = 1 +
( R1 )
T H F
R2
MAX9923 VERSION GAIN 25 100 250
Detailed Description
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 25V (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. 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.
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.)
10
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
5V VOUT - VREF 2.5V AV = 100
CHARGE CURRENT
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 (1k 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.
25mV
-25mV
0
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.
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 1A. 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 1A each.
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 0.1F 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.
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.
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11
Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Optional Noise Reduction Capacitor
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. 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.
Sense Resistor Connections
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
12
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Ultra-Precision, High-Side Current-Sense Amplifiers MAX9922/MAX9923
Typical Operating Circuits
Unidirectional Mode
VSENSE
BATT 1.9V TO 28V 3.3V
RSB VDD
RS+
RS-
RLOAD
OUT
12-BIT ADC 1nF*
ON OFF
MAX9923T MAX9923H MAX9923F
SHDN GND
FB REF
*OPTIONAL NOISE REDUCTION
Bidirectional Mode
VSENSE TO WALL-CUBE/CHARGER BATT 1.9V TO 28V 3.3V RS+ RSRLOAD
RSB VDD
OUT
ON OFF
MAX9923T MAX9923H MAX9923F
SHDN GND
1nF* FB REF 1.25V
12-BIT ADC VREF = 2.5V
*OPTIONAL NOISE REDUCTION
Chip Information
PROCESS: BiCMOS
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13
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 10 MAX PACKAGE CODE U10-2 DOCUMENT NO. 21-0061
10LUMAX.EPS

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