MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
EVALUATION KIT AVAILABLE
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
General Description
The MAX9928/MAX9929 low-cost, uni-/bidirectional,
high-side, current-sense amplifiers are ideal for monitor-
ing battery charge and discharge currents in notebooks,
cell phones, and other portable equipment. These devices
feature a wide -0.1V to +28V input common-mode voltage
range, low 20μA supply current with VOS less than 0.4mV,
and a gain accuracy better than 1.0%. The input common-
mode range is independent of the supply voltage, ensur-
ing that the current-sense information remains accurate
even when the measurement rail is shorted to ground.
The MAX9928F features a current output with a transcon-
ductance ratio of 5μA/mV. An external resistor converts
the output current to a voltage, allowing adjustable gain
so that the input sense voltage can be matched to the
maximum ADC input swing. The MAX9929F has a volt-
age output and integrates a 10kΩ output resistor for a
fixed voltage gain of 50V/V.
A digital SIGN output indicates direction of current flow, so
the user can utilize the full ADC input range for measuring
both charging and discharging currents.
The MAX9928/MAX9929 are fully specified over the
-40°C to +125°C automotive temperature range, and
available in 6-bump UCSP™ (1mm x 1.5mm) and 8-pin
μMAX® packages. The UCSP package is bump-to-bump
compatible with the MAX4372_EBT.
Features
Wide -0.1V to +28V Common-Mode Range,
Independent of Supply Voltage
● 2.5V to 5.5V Operating Supply Voltage
20μA Quiescent Supply Current
0.4mV (max) Input Offset Voltage
Gain Accuracy Better than 1% (max)
SIGN Output Indicates Current Polarity
● Transconductance and Gain Versions Available
• 5μA/mV (MAX9928F)
• 50V/V (MAX9929F)
Pin Compatible with the MAX4372 in UCSP
Available in Ultra-Small, 3x2 UCSP
(1mm x 1.5mm) and 8-Pin μMAX Packages
Applications
Monitoring Charge/Discharge Currents in Portable/
Battery-Powered Systems
Notebook Computers
General-System/Board-Level Current Monitoring
Smart-Battery Packs/Chargers
Precision Current Sources
Smart Cell Phones
Super Capacitor Charge/Discharge
UCSP is a trademark and μMAX is a registered trademark of
Maxim Integrated Products, Inc.
Pin Configurations and Typical Operating Circuit appear at
end of data sheet.
Ordering Information
PART
OUTPUT TYPE
GAIN
PIN-PACKAGE
MAX9928FAUA+
Current
Gm = 5μA/mV
8 μMAX
MAX9928FABT+T
Current
Gm = 5μA/mV
3x2 UCSP
MAX9929FAUA+
Voltage
AV = 50V/V
8 μMAX
MAX9929FABT+T
Voltage
AV = 50V/V
3x2 UCSP
Note: All devices are specified over the -40°C to +125°C operating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
TOP MARK
+AAF
+ADI
19-4251; Rev 4; 9/14


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Absolute Maximum Ratings
VCC, SIGN to GND..................................................-0.3V to +6V
RS+, RS- to GND...................................................-0.3V to +30V
OUT to GND.............................................. -0.3V to (VCC + 0.3V)
Differential Input Voltage (VRS+ - VRS-)...............................±30V
OUT, SIGN Short Circuit to VCC or GND...................Continuous
Current into Any Pin..........................................................±20mA
Continuous Power Dissipation (TA = +70°C)
6-Bump 1mm x 1.5mm UCSP
(derate 3.9mW/°C above +70°C)...........................308.3mW
8-Pin μMAX (derate 4.8mW/°C above +70°C).............388mW
Operating Temperature Range.......................... -40°C to +125°C
Storage Temperature Range............................. -65°C to +150°C
Junction Temperature.......................................................+150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°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
(VRS+ = -0.1V to +28V, VCC = 3.3V, VSENSE = (VRS+ - VRS-) = 0V, ROUT = 10kΩ for MAX9928F, TA = -40°C to +125°C, unless oth-
erwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
AMPLIFIER DC ELECTRICAL CHARACTERISTICS
Input Offset Voltage (Note 2)
VOS
VRS+ = 3.6V
VRS+ = -0.1V
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = -40°C to +125°C
±0.1
±0.6
±0.4
±0.8
±1.0
±3.0
mV
Common-Mode Input Range
VCMR (Note 3)
-0.1 +28 V
Common-Mode Rejection Ratio
CMRR
2V ≤ VRS+ ≤ 28V
TA = +25°C
TA = -40°C to +125°C
93
87
104
-0.1V ≤ VRS+
TA = +25°C
60 72
+2V
TA = -40°C to +125°C
54
dB
Full-Scale Sense Voltage (Note 2) VSENSE MAX992_F
±50 mV
Gain (Note 2)
AV MAX9929F
50 V/V
Gain Accuracy (Notes 2, 6)
MAX9929F,
VRS+ = 3.6V
MAX9929F,
VRS+ = -0.1V
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = -40°C to +125°C
±0.3
±0.3
±1.0
±2.5
±1.0
±2.8
%
Transconductance (Note 2)
GM MAX9928F
5 µA/mV
Transconductance Accuracy
(Note 2)
MAX9928F,
VRS+ = 3.6V
MAX9928F,
VRS+ = -0.1V
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = -40°C to +125°C
±0.3
±0.3
±1.0
±2.5
±1.0
±2.8
%
Input Bias Current (Note 4)
IRS+, IRS-
2V ≤ VRS+ ≤ 28V
-0.1V ≤ VRS+ ≤ +2V
0 1.6 6
-80 +6
µA
Input Offset Bias Current (Note 4)
IOS
2V ≤ VRS+ ≤ 28V
-0.1V ≤ VRS+ ≤ +2V
±0.05
±0.2
±1
±2
µA
Input Leakage Current
IRS+, IRS- VCC = 0V, VRS+ = VRS- = 28V (Note 5)
0.05 1.0
µA
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Maxim Integrated │2


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Electrical Characteristics (continued)
(VRS+ = -0.1V to +28V, VCC = 3.3V, VSENSE = (VRS+ - VRS-) = 0V, ROUT = 10kΩ for MAX9928F, TA = -40°C to +125°C, unless oth-
erwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
Output Resistance
SYMBOL
ROUT
MAX9928F
MAX9929F
CONDITIONS
­Output High Voltage (Note 6)
VOH
MAX9928F, ROUT = 10kΩ
MAX9929F
Minimum Output Voltage (Note 7)
VOL MAX9929F
Minimum Output Current (Note 7)
IOL MAX9928F
SIGN COMPARATOR DC ELECTRICAL CHARACTERISTICS
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = -40°C to +125°C
Discharge to Charge Trip Point
(Note 8)
Charge to Discharge Trip Point
(Note 8)
Hysteresis Width
Common-Mode Input Range
(Note 9)
VTDC
VTCD
VHYS
VCMR
VRS+ = 3.6V
VRS+ = -0.1V
VRS+ = 3.6V
VRS+ = -0.1V
VRS+ = 3.6V, -0.1V
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = -40°C to +125°C
TA = +25°C
TA = +25°C
TA = +25°C
Common-Mode Rejection Ratio
(Note 9)
Output Low Voltage
CMRR
VOL
2V ≤ VRS+ ≤ 28V
-0.1V ≤ VRS+ ≤ +2V
ISINK = 100µA
Output High Voltage
VOH
MIN TYP MAX UNITS
5 MΩ
6.4 10 13.6 kΩ
(VCC -
0.1)
(VCC -
0.1)
(VCC -
0.45)
(VCC -
0.45)
V
0.25
2.0
15
mV
0.025
0.2
1.5
µA
-1.6
-2.15
-2.5
-4.6
-0.1
-1.2 -0.5
-0.15
-1.2 +0.25
+2.3
-1.8
-1.8
0.6
+28
102
74
0.03
(VCC -
0.01)
0.1
(VCC -
0.04)
mV
mV
mV
V
dB
V
V
Internal Pullup Resistor
RPULL-UP
1 MΩ
POWER SUPPLY
Supply Voltage Range (Note 10)
Amplifier Power-Supply Rejection
Ratio (Note 10)
Comparator Power-Supply
Rejection Ratio
Quiescent Supply Current
VCC
PSRRA
PSRRC
ICC
TA = +25°C
TA = -40°C to +125°C
VRS+ = 3.6V
VRS+ = -0.1V
VRS+ = 3.6V
VRS+ = -0.1V
2V ≤ VRS+ ≤ 28V
-0.1V ≤ VRS+ < +2V
2.5 5.5
2.8 5.5
72 90
66 86
90
86
20 30
115 200
V
dB
dB
µA
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Maxim Integrated │3


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Electrical Characteristics (continued)
(VRS+ = -0.1V to +28V, VCC = 3.3V, VSENSE = (VRS+ - VRS-) = 0V, ROUT = 10kΩ for MAX9928F, TA = -40°C to +125°C, unless oth-
erwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
AC ELECTRICAL CHARACTERISTICS
-3dB Bandwidth
OUT Settling to 1% of Final Value
BW
tSET
MAX992_F, VSENSE = 50mV
VRS+ = 3.6V,
CLOAD = 10pF,
ROUT = 10kΩ for
MAX9928F
MAX992_F, VSENSE =
5mV to 50mV step
MAX992_F, VSENSE =
50mV to 5mV step
150
6
15
kHz
µs
SIGN Comparator Propagation
Delay (Low to High)
Overdrive = 1mV
tPROP_LH Overdrive = 5mV
80
µs
30
SIGN Comparator Propagation
Delay (High to Low)
Overdrive = 1mV
tPROP_HL Overdrive = 5mV
50
µs
13
Power-Up Time to 1% of Final
Value
Saturation Recovery Time
VSENSE = 50mV for MAX992_F,
VRS+ = 3.6V, CLOAD = 10pF
100mV ≤ VSENSE P 50mV for MAX992_F,
VRS+ = 3.6V, CLOAD = 10pF
50 µs
4 ms
Note 1:
Note 2:
All devices are 100% production tested at TA = +25°C. All temperature limits are guaranteed by design.
VOS is extrapolated from two point transconductance and gain accuracy tests. Measurements are made at VSENSE = +5mV
and VSENSE = +50mV for MAX992_F. These measurements are also used to test the full-scale sense voltage, transcon-
ductance, and gain. These VOS specifications are for the trimmed direction only (VRS+ > VRS-). For current flowing in the
oSpepeotshieteDdeirteacilteiodnD(VesRcSr-ip>tioVnRfSo+r),mVoOreS
is ±1mV (max)
information.
at
+25°C
and
±1.8mV
(max)
over
temperature,
when
VRS+
is
at
3.6V.
Note 3: Guaranteed by common-mode rejection ratio. Extrapolated VOS as described in Note 2 is used to calculate common-mode
rejection ratio.
Note 4: Includes input bias current of SIGN comparator.
Note 5: Leakage in to RS+ or RS- when VCC = 0V. Includes input leakage current of SIGN comparator. This specification does not
add to the bias current.
Note 6: Output voltage should be 650mV below VCC to achieve full accuracy.
Note 7: IOL is the minimum output current in the VSENSE - IOUT transfer characteristics. VOL is the minimum output voltage in the
VSENSE - VOUT transfer characteristic.
Note 8: VSENSE voltage required to switch comparator.
Note 9: Discharge to charge trip point is functionally tested at VCM = -0.1V, +3.6V, and +28V.
Note 10: Guaranteed by PSRR test. Extrapolated VOS as described in Note 2 is used to calculate the power-supply rejection ratio.
VSENSE has to be such that the output voltage is 650mV below VCC to achieve full accuracy.
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Maxim Integrated │4


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Typical Operating Characteristics
(VCC = 3.3V, VRS+ = 12V, TA = +25°C, unless otherwise noted.)
VOS HISTOGRAM
45
AV = 50V/V
40
35
30
25
20
15
10
5
0
-0.40 -0.30 -0.20 -0.10 0 0.10 0.20 0.30 0.40
VOS (mV)
GAIN ACCURACY
HISTOGRAM
30
AV = 50V/V
25
20
15
10
5
0
-1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0
GAIN ACCURACY (%)
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
-1
OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
0123
COMMON-MODE VOLTAGE (V)
28
OFFSET VOLTAGE vs. TEMPERATURE
1.0
0.8 VCM = 3.6V
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
150
VSENSE = 0V
125 VRS+ = 0V
100
75
50
VRS+ = 3.6V
25
0
2.5
3.0 3.5 4.0 4.5 5.0
SUPPLY VOLTAGE (V)
5.5
SUPPLY CURRENT
vs. COMMON-MODE VOLTAGE
150
120
90 VCC = 5.5V
60
VCC = 2.5V
30
0
-0.5
0 0.5 1.0 1.5 2.0
COMMON-MODE VOLTAGE (V)
28
SUPPLY CURRENT
vs. TEMPERATURE
150
VSENSE = 0V
125
VRS+ = 0V
100
75
50
VRS+ = 3.6V
25
0
-50 -25
0 25 50 75 100 125
TEMPERATURE (°C)
INPUT BIAS CURRENT
vs. COMMON-MODE VOLTAGE
10
0
-10
-20
-30
-40
-50
-60
-70
-80 -2 -0.10 2 4 6 8 10
COMMON-MODE VOLTAGE (V)
28
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Maxim Integrated │5


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = 12V, TA = +25°C, unless otherwise noted.)
MAX9928F
IOUT vs. VSENSE
2500
VOUT = 0V
TA = -40°C
2000
1500 TA = +25°C
TA = +125°C
1000
500
6
5
4
3
2
1
MAX9929F
VOUT vs. VSENSE
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
VCC = 2.5V
0
0 0.1 0.2 0.3 0.4 0.5
VSENSE (V)
0
0 20 40 60 80 100 120 140
VSENSE (mV)
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
2.5
GAIN ACCURACY
vs. SUPPLY VOLTAGE
3.0 3.5 4.0 4.5 5.0
SUPPLY VOLTAGE (V)
5.5
MINIMUM OUTPUT VOLTAGE
vs. TEMPERATURE
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
SMALL-SIGNAL GAIN
vs. FREQUENCY
35
VCM = 3.6V
32 MAX992_F
29
26
23
120
90
60
30
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
30
MAX9929F
VOUT vs. VSENSE
TA = -40°C
TA = +25°C
TA = +125°C
40 50 60 70 80 90
VSENSE (mV)
GAIN ACCURACY vs. TEMPERATURE
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
CMRR vs. FREQUENCY
20
0.01
0.1 1 10 100
FREQUENCY (kHz)
1000
0
10 100 1k 10k 100k 1M
FREQUENCY (Hz)
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MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Typical Operating Characteristics (continued)
(VCC = 3.3V, VRS+ = 12V, TA = +25°C, unless otherwise noted.)
20
0
-20
-40
-60
-80
-100
-120
0.1
PSRR vs. FREQUENCY
1 10 100 1k 10k 100k
FREQUENCY (Hz)
4
3
2
1
0
150
100
50
0
-3
VSIGN AND VOUT
vs. VSENSE
-2 -1 0 1
VSENSE (mV)
2
3
VSENSE
VOUT
MAX9929F LARGE-SIGNAL
TRANSIENT RESPONSE
MAX9928 toc18
50mV/div
1V/div
100µs/div
OVERDRIVE RECOVERY
MAX9928 toc20
VSENSE
100mV/div
400µs/div
VOUT
500mV/div
COMPARATOR PROPAGATION DELAY
(RS+ = 3.6V, 5mV OVERDRIVE)
MAX9928 toc21
VSENSE
2mV/div
VOUT
1V/div
POWER-UP DELAY
MAX9928 toc22
VCC
1V/div
VOUT
1V/div
40µs/div
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40µs/div
Maxim Integrated │7


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Pin Configuration
PIN
µMAX
1
BUMP
UCSP
B3
NAME
RS-
2 B2 SIGN
3 B1 RS+
4, 5 — N.C.
6 A1 VCC
7 A2 GND
8 A3 OUT
FUNCTION
Negative Current-Sense Input. Load-side connection for the external sense resistor.
SIGN Output. Indicates polarity of VSENSE.
SIGN = H indicates VRS+ > VRS-
SIGN = L indicates VRS+ < VRS-
Positive Current-Sense Input. Power-side connection to the external sense resistor.
No Connection. Not internally connected.
Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.
Circuit Ground
Current-Sense Output. MAX9928: Current output (IOUT is proportional to |VSENSE|). MAX9929:
Voltage output (VOUT is proportional to |VSENSE|).
Detailed Description
The MAX9928F/MAX9929F micropower uni-/bidirection-
al, current-sense amplifiers feature -0.1V to +28V input
common-mode range that is independent of the supply
voltage. This wide input voltage range feature allows the
monitoring of the current flow out of a power supply during
short-circuit/fault conditions, and also enables highside
current sensing at voltages far in excess of the supply
voltage (VCC). The MAX9928F/MAX9929F operate from
a 2.5V to 5.5V single supply and draw a low 20μA quies-
cent supply current.
Current flows through the sense resistor, generating a
sense voltage VSENSE (Figure 1). The comparator sens-
es the direction of the sense voltage and configures the
amplifier for either positive or negative sense voltages by
controlling the S1 and S2 switches.
For positive VSENSE voltage, the amplifier’s inverting
input is high impedance and equals VIN - VSENSE. The
amplifier’s output drives the base of Q1, forcing its non-
inverting input terminal to (VIN - VSENSE); this causes
a current to flow through RG1 equal to |VSENSE|/RG1.
Transistor Q2 and the current mirror amplify the current
by a factor of M.
For negative VSENSE voltage, the amplifier’s noninverting
input is high impedance and the voltage on RS- terminal
equals VIN + VSENSE. The amplifier’s output drives the
base of Q1 forcing its inverting input terminal to match
the voltage at the noninverting input terminal; this causes
a current to flow through RG2 equal to |VSENSE|/RG2.
Again, transistor Q2 and the current mirror amplify the
current by a factor of M.
+VSENSE vs. -VSENSE
The amplifier is configured for either positive VSENSE or
negative VSENSE by the SIGN comparator. The compara-
tor has a built-in offset skew of -1.2mV so that random
offsets in the comparator do not affect the precision of
IOUT (VOUT) with positive VSENSE. The comparator has
a small amount of hysteresis (typically 0.6mV) to prevent
its output from oscillating at the crossover sense voltage.
The ideal transfer characteristic of IOUT (VOUT) and the
output of the comparator (SIGN) is shown in Figure 2.
The amplifier VOS is only trimmed for the positive
VSENSE voltages (VRS+ > VRS-). The SIGN comparator
reconfigures the internal structure of the amplifier to work
with negative VSENSE voltages (VRS- > VRS+) and the
piCnrhgeacVrisaOicoStneirsiVssOtilcSigshtNrtilmyoteimis2p.naTochteleodnu.gsSeeerreceafdfneectcathiivloseoisnaentdhtheethEdelierrecectsrtiuicolatn-l
that needs the best precision to be the direction where
VRS+ > VRS-. For example, when monitoring Li+ battery
currents, the discharge current should be VRS+ > VRS- to
give the best accuracy over the largest dynamic range.
When the battery charger is plugged in, the charge cur-
rent flows in the opposite direction and is usually much
lTayrpgiecra,laOnpdearahtiinggheCrirVcOuiSt. error can be tolerated. See the
For applications with unidirectional currents (e.g., battery
discharge only), the SIGN output can be ignored.
Note that as VSENSE increases, the output current (IOUT
for the MAX9928 or VOUT/10kΩ for the MAX9929) also
increases. This additional current is supplied from VCC.
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Maxim Integrated │8


MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
2.5V TO 5.5V
VCC
RC1
80k
RC2
80k
VIN
-0.1V TO +28V
(VBATT)
+
RS+
RG1
80k
RS-
-
RG2
80k
TO
LOAD/CHARGER
*INTERNAL 10kRESISTOR FOR MAX9929_ ONLY.
C
A S1
MAX9928F
MAX9929F
VCC
1M
SIGN
TO C
CURRENT
MIRROR
S2 OUT
TO ADC
Q2
Q1
10k*
GND
Figure 1. Functional Diagram
-3.0 -1.8 -1.2 0 1.0 2.0 3.0
VSENSE (mV)
-3.0 -1.8 -1.2 0 1.0 2.0 3.0
VSENSE (mV)
( ) FOR THE MAX9929F.
Figure 2. Ideal Transfer Characteristics with 0mV Amplifier
Input Offset Voltage and -1mV Comparator Input Offset Voltage
For both positive and negative VSENSE voltages, the cur-
rent flowing out of the current mirror is equal to:
IOUT = M x |VSENSE|/RG1
For the MAX9928F, the transconductance of the device
is trimmed so that IOUT/|VSENSE| = 5μA/mV. For the
MAX9929F, the voltage gain of the device is trimmed so
that VOUT/|VSENSE| = 50V/V. The SIGN output from the
comparator indicates the polarity of VSENSE.
Current Output (MAX9928F)
The output voltage equation for the MAX9928_ is given
below:
VOUT = (RSENSE x ILOAD) x (Gm X ROUT)
where VOUT = the desired full-scale output voltage, ILOAD
= the full-scale current being sensed, RSENSE = the
current-sense resistor, ROUT = the voltage-setting resis-
tor, and Gm = MAX9928F transconductance (5μA/mV).
The full-scale output voltage range can be set by chang-
ing the ROUT resistor value. The above equation can be
modified to determine the ROUT required for a particular
full-scale range:
ROUT = (VOUT)/(ILOAD x RSENSE x Gm)
OUT is a high-impedance current source and can drive an
unlimited amount of capacitance.
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MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Voltage Output (MAX9929F)
The output voltage equation for the MAX9929_ is given
below:
VOUT = (RSENSE x ILOAD) x (AV)
where VOUT = the desired full-scale output voltage,
ILOAD = the full-scale current being sensed, RSENSE =
the current-sense resistor, AV = MAX9929F voltage gain
(50V/V).
SIGN Output
The current/voltage at OUT indicates magnitude. The
SIGN output indicates the current’s direction. The SIGN
comparator compares RS+ to RS-. The sign output is high
when RS+ is greater than RS- indicating positive current
flow. The sign output is low when RS- is greater than RS+
indicating negative current flow. In battery-operated sys-
tems, this is useful for determining whether the battery is
charging or discharging. The SIGN output might not cor-
rectly indicate the direction of load current when VSENSE
is between -1.8mV to -1.2mV (see Figure 2). Comparator
hysteresis of 0.6mV prevents oscillation of SIGN output. If
current direction is not needed, leave SIGN unconnected.
Applications Information
Choosing RSENSE
The MAX9928F/MAX9929F operate over a wide variety
of current ranges with different sense resistors. Adjust the
RSENSE value to monitor higher or lower current levels.
Select RSENSE using these guidelines:
● Voltage Loss: A high RSENSE value causes the
power-source voltage to drop due to IR loss. For least
voltage loss, use the lowest RSENSE value.
● Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately. This is be-
cause offsets become less significant when the sense
voltage is larger.
● Efficiency and Power Dissipation: At high current
levels, the I2R losses in RSENSE might be significant.
Take this into consideration when choosing the resis-
tor value and power dissipation (wattage) rating. Also,
if the sense resistor is allowed to heat up excessively,
its value could drift.
● Inductance: If there is a large high-frequency compo-
nent to ISENSE, keep inductance low. Wire-wound re-
sistors have the highest inductance, while metal film
is somewhat better. Low-inductance metal-film resis-
tors are available. Instead of being spiral wrapped
around a core, as in metal film or wirewound resistors,
these are a straight band of metal. They are made in
values under 1Ω.
Use in Systems with Super Capacitors
Since the input common-mode voltage range of the
MAX9928/MAX9929 extends all the way from -0.1V to
28V, they are ideal to use in applications that require use
of super capacitors for temporary or emergency energy
storage systems. Some modern industrial systems use
multifarad (1F–50F) capacitor banks to supply enough
energy to keep critical systems alive even if the primary
power source is removed or temporarily disabled. Unlike
batteries, these capacitors can discharge all the way down
to 0V. The MAX9928/MAX9929 can continuously help
monitor their health and state of charge/discharge.
UCSP Applications Information
For the latest application details on UCSP construc-
tion, dimensions, tape carrier information, PCB tech-
niques, bump-pad layout, and recommended reflow
temperature profile, as well as the latest information
on reliability testing results, go to Maxim’s website at
www.maximintegrated.com/ucsp to find Application
Note 1891: Wafer-Level Packaging (WLP) and its
Applications.
Chip Information
PROCESS: BiCMOS
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MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Pin Configurations
TOP VIEW
+
RS- 1
SIGN 2 MAX9928F
MAX9929F
RS+ 3
N.C. 4
8 OUT
7 GND
6 VCC
5 N.C.
µMAX
TOP VIEW
(BUMPS ON THE BOTTOM)
1
2
3
A VCC
GND OUT
MAX9928F
MAX9929F
B RS+
SIGN
RS-
UCSP
(1mm x 1.5mm)
Typical Operating Circuit
VIN
-0.1V TO
+28V
2.5V TO
5.5V
0.1µF
RSENSE
RS+ RS-
VCC
MAX9928F
MAX9929F
SIGN
OUT
GND
*FOR THE MAX9928F ONLY
WALL-CUBE
CHARGER
LOAD
µC
DIGITAL
INPUT
ROUT*
ADC
GND
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MAX9928 (Maxim Integrated Products)
(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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
8 μMAX
6 UCSP
PACKAGE CODE
U8+1
B6+1
OUTLINE NO.
21-0036
21-0097
LAND PATTERN NO.
90-0092
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(MAX9928 / MAX9929) Current-Sense Amplifiers

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MAX9928/MAX9929
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
Revision History
REVISION
NUMBER
0
1
2
3
4
REVISION
DATE
DESCRIPTION
12/08 Initial release
8/09 Removed MAX9928T and MAX9929T from data sheet
4/11 Updated top marks
4/12 Removed the R61A1+1 package code note and references
9/14 Removed automotive reference from data sheet.
PAGES
CHANGED
1–5, 7–12
1
1
10
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2014 Maxim Integrated Products, Inc. │13




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