19-4429; Rev 1; 1/10
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 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
TEMP
RANGE
GAIN (V/V)
Adjustable
MAX9922EUB+
10 µMAX
-40°C to +85°C
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 = 0V, VREF = VDD/2 for bidirectional, VREF = 0V for unidirectional, VSENSE = VRS+ - VRS= 0V, 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 = 0V,
VREF = VDD/2, -40°C ≤ TA ≤ +85°C
±0.1
±10
MAX9923T, VSENSE = 0V, VREF = VDD/2,
-40°C ≤ TA ≤ +85°C
±0.2
±25
MAX9923H, VSENSE = 0V, VREF = VDD/2
-40°C ≤ TA ≤ +85°C
±0.2
±20
MAX9923F, VSENSE = 0V, 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 = 0V,
VREF = VDD/2, -40°C ≤ TA ≤ +85°C
±0.05
MAX9923T, VSENSE = 0V, VREF = VDD/2,
-40°C ≤ TA ≤ +85°C
±0.20
MAX9923H, VSENSE = 0V, VREF = VDD/2,
-40°C ≤ TA ≤ +85°C
±0.10
MAX9923F, VSENSE = 0V, 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 = 0V, VREF = VDD/2 for bidirectional, VREF = 0V for unidirectional, VSENSE = VRS+ - VRS= 0V, 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)
∆AV
Gain Nonlinearity
~AV
Open-Loop Gain
AVOL
Input Bias Current
MIN
TA = +25°C
TYP
±0.17
-40°C ≤ TA ≤ +85°C
±0.12
-40°C ≤ TA ≤ +85°C
MAX9923F
-40°C ≤ TA ≤ +85°C
±0.40
±0.30
±0.60
TA = +25°C
-40°C ≤ TA ≤ +85°C
UNITS
±0.60
TA = +25°C
MAX9923H
MAX
±0.24
±0.40
%
±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
TA = +25°C
0
VDD 1.4
-40°C ≤ TA ≤ +85°C
0
VDD 1.6
0 ≤ REF ≤ VDD - 1.4V (Note 2)
94
100
OUT High Voltage
VOH
MAX9923T (bidirectional)
±60
±70
MAX9923H (bidirectional)
±16
±20
MAX9923F (bidirectional)
±6
±7
7
30
VOH = VDD – VOUT
(Note 7)
RL = 10kΩ to GND and REF = GND
1
10
RL = 10kΩ to VDD and REF = VDD - 1.4
6
30
SHDN Logic-Low
VIL
VDD = 5.5V
SHDN Logic-High
VIH
VDD = 5.5V
µA
mV
RL = 10kΩ to VDD
and REF = VDD - 1.4
6
VOL
IIH/IIL
RL = 10kΩ to GND
and REF = GND
1
OUT Low Voltage (Note 7)
SHDN Input Current
dB
±20
MAX9922 (bidirectional)
REF Input Current
(Note 6)
V
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 = 0V, VREF = VDD/2 for bidirectional, VREF = 0V for unidirectional, VSENSE = VRS+ - VRS= 0V, 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
∆VOUT = 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
300
VRSB = 12V
200
V SHDN = 0.3V
0.05
1
IRSB_SD
V SHDN = 0.3V, VRSB = 28V
0.05
1
VDD = VREF = 0V, 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 = 0V, VREF = VDD/2 for bidirectional, VREF = 0V for unidirectional, VSENSE = VRS+ - VRS= 0V, 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 = 0V, VRSB = VRS+ = VRS- = 28V
CONDITIONS
MIN
0.05
1
µA
MAX9922, AV = 100V/V, VREF = 0V, VSENSE =
10mV, VDD = 0V 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 = 0V 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 V REF = V DD /2 while maintaining gain accuracy. 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. The input
bias current for REF is typically 1pA in the MAX9922 since it connects to the gate of a MOS transistor. 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
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.
Current-Sense Amplifier Input Stage Supply. Connect to either RS+ or RS-.
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 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 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. 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.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
10 µMAX
U10-2
21-0061
10LUMAX.EPS
MAX9922/MAX9923
Ultra-Precision, High-Side
Current-Sense Amplifiers
α
α
14
______________________________________________________________________________________
Ultra-Precision, High-Side
Current-Sense Amplifiers
REVISION
NUMBER
REVISION
DATE
0
3/09
Initial release
1
1/10
Updated conditions for REF input current and Note 6
DESCRIPTION
PAGES
CHANGED
—
3, 5
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 ____________________ 15
© 2010 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX9922/MAX9923
Revision History
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