General Description
The MAX4080/MAX4081 are high-side, current-sense
amplifiers with an input voltage range that extends from
4.5V to 76V making them ideal for telecom, automotive,
backplane, and other systems where high-voltage cur-
rent monitoring is critical. The MAX4080 is designed for
unidirectional current-sense applications and the
MAX4081 allows bidirectional current sensing. The
MAX4081 single output pin continuously monitors the
transition from charge to discharge and avoids the
need for a separate polarity output. The MAX4081
requires an external reference to set the zero-current
output level (VSENSE = 0V). The charging current is rep-
resented by an output voltage from VREF to VCC, while
discharge current is given from VREF to GND.
For maximum versatility, the 76V input voltage range
applies independently to both supply voltage (VCC)
and common-mode input voltage (VRS+). High-side
current monitoring does not interfere with the ground
path of the load being measured, making the
MAX4080/MAX4081 particularly useful in a wide range
of high-voltage systems.
The combination of three gain versions (5V/V, 20V/V,
60V/V = F, T, S suffix) and a user-selectable, external
sense resistor sets the full-scale current reading and its
proportional output voltage. The MAX4080/MAX4081
offer a high level of integration, resulting in a simple,
accurate, and compact current-sense solution.
The MAX4080/MAX4081 operate from a 4.5V to 76V sin-
gle supply and draw only 75µA of supply current. These
devices are specified over the automotive operating
temperature range (-40°C to +125°C) and are available
in a space-saving 8-pin µMAX®or SO package.
Applications
Automotive (12V, 24V, or 42V Batteries)
48V Telecom and Backplane Current
Measurement
Bidirectional Motor Control
Power-Management Systems
Avalanche Photodiode and PIN-Diode Current
Monitoring
General System/Board-Level Current Sensing
Precision High-Voltage Current Sources
Features
♦Wide 4.5V to 76V Input Common-Mode Range
♦Bidirectional or Unidirectional ISENSE
♦Low-Cost, Compact, Current-Sense Solution
♦Three Gain Versions Available
5V/V (MAX4080F/MAX4081F)
20V/V (MAX4080T/MAX4081T)
60V/V (MAX4080S/MAX4081S)
♦±0.1% Full-Scale Accuracy
♦Low 100µV Input Offset Voltage
♦Independent Operating Supply Voltage
♦75µA Supply Current (MAX4080)
♦Reference Input for Bidirectional OUT (MAX4081)
♦Available in a Space-Saving, 8-Pin µMAX Package
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
________________________________________________________________
Maxim Integrated Products
1
N.C.
OUTGND
1
2
8
7
RS-
N.C.VCC
N.C.
RS+
μMAX/SO
TOP VIEW
3
4
6
5
MAX4080
REF1B
OUTGND
1
2
8
7
RS-
REF1AVCC
N.C.
RS+
μMAX/SO
3
4
6
5
MAX4081
Pin Configurations
Ordering Information
19-2562; Rev 1; 11/08
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.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX4080FAUA -40°C to +125°C 8 µMAX
MAX4080FASA -40°C to +125°C 8 SO
MAX4080TAUA -40°C to +125°C 8 µMAX
MAX4080TASA -40°C to +125°C 8 SO
MAX4080SAUA -40°C to +125°C 8 µMAX
MAX4080SASA -40°C to +125°C 8 SO
MAX4081FAUA -40°C to +125°C 8 µMAX
MAX4081FASA -40°C to +125°C 8 SO
MAX4081TAUA -40°C to +125°C 8 µMAX
MAX4081TASA -40°C to +125°C 8 SO
MAX4081SAUA -40°C to +125°C 8 µMAX
MAX4081SASA -40°C to +125°C 8 SO
Selector Guide appears at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
VCC to GND............................................................-0.3V to +80V
RS+, RS- to GND....................................................-0.3V to +80V
OUT to GND.............-0.3V to the lesser of +18V or (VCC + 0.3V)
REF1A, REF1B to GND
(MAX4081 Only)....-0.3V to the lesser of +18V or (VCC + 0.3V)
Output Short Circuit to GND.......................................Continuous
Differential Input Voltage (VRS+ - VRS-)...............................±80V
Current into Any Pin..........................................................±20mA
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 4.5mW/°C above +70°C) .............362mW
8-Pin SO (derate 5.88mW/°C above +70°C)................471mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
DC ELECTRICAL CHARACTERISTICS
(VCC = VRS+ = 4.5V to 76V, VREF1A = VREF1B = 5V (MAX4081 only), VSENSE = (VRS+ - VRS-) = 0V, RLOAD = 100kΩ, TA= TMIN to
TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Voltage Range VCC Inferred from PSRR test 4.5 76 V
Common-Mode Range CMVR Inferred from CMRR test (Note 3) 4.5 76 V
MAX4080 75 190
Supply Current ICC VCC = VRS+ = 76V,
no load MAX4081 103 190 µA
Leakage Current IRS+, IRS- VCC = 0V, VRS+ = 76V 0.01 2 µA
Input Bias Current IRS+, IRS- VCC = VRS+ = 76V 5 12 µA
MAX4080F/MAX4081F ±1000
MAX4080T/MAX4081T ±250
Full-Scale Sense Voltage (Note 4) VSENSE
MAX4080S/MAX4081S ±100
mV
MAX4080F/MAX4081F 5
MAX4080T/MAX4081T 20Gain AV
MAX4080S/MAX4081S 60
V/V
TA = +25°C±0.1 ±0.6
TA = -40°C to +85°C±1Gain Accuracy ΔAVVCC = VRS+ = 48V
(Note 5)
TA = TMIN to TMAX ±1.2
%
TA = +25°C ±0.1 ±0.6
TA = -40°C to +85°C±1
Input Offset Voltage VOS VCC = VRS+ = 48V
(Note 6) TA = TMIN to TMAX ±1.2
mV
Common-Mode Rejection Ratio CMRR VCC = 48V, VRS+ = 4.5V to 76V 100 124 dB
Power-Supply Rejection Ratio PSRR VRS+ = 48V, VCC = 4.5V to 76V 100 122 dB
MAX4080F/MAX4081F,
VSENSE = 1000mV
MAX4080T/MAX4081T,
VSENSE = 250mV
OUT High Voltage (VCC -
VOH)
VCC = 4.5V, VRS+
= 48V, VREF1A =
VREF1B = 2.5V,
IOUT (sourcing) =
+500µA (Note 8) MAX4080S/MAX4081S,
VSENSE = 100mV
0.15 0.27 V
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
_______________________________________________________________________________________ 3
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = VRS+ = 4.5V to 76V, VREF1A = VREF1B = 5V (MAX4081 only), VSENSE = (VRS+ - VRS-) = 0V, RLOAD = 100kΩ, TA= TMIN to
TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
IOUT (sinking) = 10µA 4 15
OUT Low Voltage VOL
VCC = VRS+ = 48V,
VREF1A = VREF1B =
2.5V, VSENSE =
-1000mV (for
MAX4081 only)
IOUT (sinking) =
100µA 23 55
mV
REF1A = REF1B Input Voltage
Range (MAX4081 Only)
(VREF -
GND)
Inferred from REF1A rejection ratio,
VREF1A = VREF1B 1.5 6 V
REF1A Input Voltage Range
(MAX4081 Only)
(VREF1A -
GND)
Inferred from REF1A rejection ratio,
VREF1B = GND 312V
REF1A Rejection Ratio
(MAX4081 Only)
VCC = VRS+ = 48V, VSENSE = 0V,
VREF1A = VREF1B = 1.5V to 6V 80 108 dB
REF/REF1A Ratio
(MAX4081 Only)
VREF1A = 10V, VREF1B = GND,
VCC = VRS+ = 48V (Note 2) 0.497 0.500 0.503
REF1A Input Impedance
(MAX4081 Only) VREF1B = GND 250 kΩ
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
4 _______________________________________________________________________________________
AC ELECTRICAL CHARACTERISTICS
(VCC = VRS+ = 4.5V to 76V, VREF1A = VREF1B = 5V (MAX4081 only), VSENSE = (VRS+ - VRS-) = 0V, RLOAD = 100kΩ, CLOAD = 20pF,
TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
MAX4080F/T/S 250
Bandwidth BW VCC = VRS+ =
48V, VOUT = 2.5V MAX4081F/T/S 150 kHz
VSENSE = 10mV to 100mV 20
OUT Settling Time to 1% of Final
Value VSENSE = 100mV to 10mV 20 µs
Capacitive-Load Stability No sustained oscillations 500 pF
Output Resistance ROUT VSENSE = 100mV 0.1 Ω
Power-Up Time V
C C
= V
RS + = 48V , V
S E NS E
= 100mV ( Note 9) 50 µs
Saturation Recovery Time (Notes 9,10) 50 µs
Note 1: All devices are 100% production tested at TA= +25°C. All temperature limits are guaranteed by design.
Note 2: VREF is defined as the average voltage of VREF1A and VREF1B. REF1B is usually connected to REF1A or GND.
VSENSE is defined as VRS+ - VRS-.
Note 3: The common-mode range at the low end of 4.5V applies to the most positive potential at RS+ or RS-. Depending on the
polarity of VSENSE and the device’s gain, either RS+ or RS- can extend below 4.5V by the device’s typical full-scale value of
VSENSE.
Note 4: Negative VSENSE applies to MAX4081 only.
Note 5: VSENSE is:
MAX4080F, 10mV to 1000mV
MAX4080T, 10mV to 250mV
MAX4080S, 10mV to 100mV
MAX4081F, -500mV to +500mV
MAX4081T, -125mV to +125mV
MAX4081S, -50mV to +50mV
Note 6: VOS is extrapolated from the gain accuracy test for the MAX4080 and measured as (VOUT - VREF)/AVat VSENSE = 0V, for the
MAX4081.
Note 7: VSENSE is:
MAX4080F, 500mV
MAX4080T, 125mV
MAX4080S, 50mV
MAX4081F/T/S, 0V
VREF1B = VREF1A = 2.5V
Note 8: Output voltage is internally clamped not to exceed 18V.
Note 9: Output settles to within 1% of final value.
Note 10: The device will not experience phase reversal when overdriven.
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
_______________________________________________________________________________________
5
0
20
15
10
5
30
25
35
-125 -75 -50 -25-100 0 25 50 75 100 125
INPUT OFFSET VOLTAGE HISTOGRAM
MAX4080 toc01
INPUT OFFSET VOLTAGE (μV)
PERCENTAGE (%)
INPUT
OFFSET
VOLTAGE
vs. TEMPERATURE
MAX4080 toc02
-300
-250
-150
-200
0
50
-50
-100
300
100
150
200
250
INPUT OFFSET VOLTAGE (μV)
-50 25 500-25 75 100 125 150
TEMPERATURE (°C)
-0.5
-0.2
-0.3
-0.4
0
-0.1
0.4
0.3
0.2
0.1
0.5
-50 -25 0 25 50 75 100 125
GAIN ACCURACY vs. TEMPERATURE
MAX4080 toc03
TEMPERATURE (°C)
GAIN ACCURACY (%)
GAIN ACCURACY vs. VCC
MAX4080 toc04
VCC (V)
GAIN ACCURACY (%)
6452402816
-0.15
-0.10
-0.05
0
-0.20
476
VRS+ = 48V
S VERSION
T VERSION
F VERSION
MAX4080 toc05
FREQUENCY (Hz)
COMMON-MODE REJECTION RATIO (dB)
100k10k1k10010
-120
-100
-110
-90
-80
-60
-70
-50
-40
-20
-30
-10
0
-130
11M
MAX4081F/T/S
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX4080 toc06
FREQUENCY (Hz)
POWER-SUPPLY REJECTION RATIO (dB)
100k10k1k10010
-120
-100
-110
-90
-80
-60
-70
-50
-40
-20
-30
-10
0
-130
11M
MAX4081F/T/S
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX4080 toc07
FREQUENCY (Hz)
REFERENCE REJECTION RATIO (dB)
-110
-90
-100
-80
-60
-70
-50
-40
-20
-30
-10
0
-120
MAX4081F/T/S
REFERENCE REJECTION RATIO
vs. FREQUENCY
10k1k100101 100k
MAX4080 toc08
FREQUENCY (kHz)
GAIN (dB)
100101
5
10
15
20
25
30
35
40
45
50
0
0.1 1000
MAX4080F/T/S
SMALL-SIGNAL GAIN vs. FREQUENCY
VSENSE = 10mV
MAX4080S
MAX4080T
MAX4080F
MAX4080 toc09
FREQUENCY (kHz)
GAIN (dB)
100101
5
10
15
20
25
30
35
40
45
50
0
0.1 1000
MAX4081F/T/S
SMALL-SIGNAL GAIN vs. FREQUENCY
VOUT = 100mVP-P
MAX4081S
MAX4081T
MAX4081F
Typical Operating Characteristics
(VCC = VRS+ = 48V, VSENSE = 0V, CLOAD = 20pF, RLOAD = ∞, TA= +25°C, unless otherwise noted.)
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = VRS+ = 48V, VSENSE = 0V, CLOAD = 20pF, RLOAD = ∞, TA= +25°C, unless otherwise noted.)
60
65
75
70
80
85
42816 40 52 64 76
MAX4080
SUPPLY CURRENT vs. VCC
MAX4080 toc10
VCC (V)
SUPPLY CURRENT (μA)
NO LOAD
VSENSE = 0V
MAX4080 toc11
VCC (V)
SUPPLY CURRENT (μA)
645216 28 40
85
90
95
100
105
110
115
120
125
476
MAX4081
SUPPLY CURRENT vs. VCC
VREF = 2.5V
NO LOAD
VSENSE = 0V
65
80
75
70
90
85
110
105
100
95
115
-50 -25 0 25 50 75 100 125
MAX4080
SUPPLY CURRENT vs. TEMPERATURE
MAX4080 toc12
TEMPERATURE (°C)
SUPPLY CURRENT (μA)
65
80
75
70
90
85
110
105
100
95
115
-50 -25 0 25 50 75 100 125
MAX4081
SUPPLY CURRENT vs. TEMPERATURE
MAX4080 toc13
TEMPERATURE (°C)
SUPPLY CURRENT (μA)
VREF1A = VREF1B = 2.5V
MAX4080 toc14
IOUT (SOURCING) (mA)
VOUT HIGH VOLTAGE (VCC - VOH) (V)
0.90.80.6 0.70.2 0.3 0.4 0.50.1
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0
0 1.0
VOUT HIGH VOLTAGE
vs. IOUT (SOURCING)
VCC = 4.5V
TA = +125°C
TA = +85°C
TA = +25°C
TA = 0°CTA = -40°C
45040035030025020015010050
50
100
150
200
250
300
0
0 500
VOUT LOW VOLTAGE
vs. IOUT (SINKING)
MAX4080 toc15
IOUT (SINKING) (μA)
VOUT LOW VOLTAGE (mV)
TA = +125°C
TA = +85°C
TA = +25°C
TA = 0°C
TA = -40°C
VCC = 4.5V
MAX4080 toc16
INPUT
5mV/div
OUTPUT
25mV/div
20μs/div
MAX4080F
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080 toc17
INPUT
5mV/div
OUTPUT
100mV/div
20μs/div
MAX4080T
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080 toc18
INPUT
5mV/div
OUTPUT
300mV/div
20μs/div
MAX4080S
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
_______________________________________________________________________________________
7
MAX4080 toc19
INPUT
10mV/div
OUTPUT
50mV/div
20μs/div
MAX4081F
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080 toc20
INPUT
2.5mV/div
OUTPUT
50mV/div
20μs/div
MAX4081T
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080 toc21
INPUT
1mV/div
OUTPUT
50mV/div
20μs/div
MAX4081S
SMALL-SIGNAL TRANSIENT RESPONSE
MAX4080 toc22
INPUT
400mV/div
OUTPUT
2V/div
20μs/div
MAX4080F
LARGE-SIGNAL TRANSIENT RESPONSE
MAX4080 toc23
INPUT
100mV/div
OUTPUT
2V/div
20μs/div
MAX4080T
LARGE-SIGNAL TRANSIENT RESPONSE
MAX4080 toc24
INPUT
33mV/div
OUTPUT
2V/div
20μs/div
MAX4080S
LARGE-SIGNAL TRANSIENT RESPONSE
MAX4080 toc25
INPUT
400mV/div
OUTPUT
2V/div
20μs/div
MAX4081F
LARGE-SIGNAL TRANSIENT RESPONSE
MAX4080 toc26
INPUT
100mV/div
OUTPUT
2V/div
20μs/div
MAX4081T
LARGE-SIGNAL TRANSIENT RESPONSE
MAX4080 toc27
INPUT
33mV/div
OUTPUT
2V/div
20μs/div
MAX4081S
LARGE-SIGNAL TRANSIENT RESPONSE
Typical Operating Characteristics (continued)
(VCC = VRS+ = 48V, VSENSE = 0V, CLOAD = 20pF, RLOAD = ∞, TA= +25°C, unless otherwise noted.)
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = VRS+ = 48V, VSENSE = 0V, CLOAD = 20pF, RLOAD = ∞, TA= +25°C, unless otherwise noted.)
MAX4080 toc28
4μs/div
VCC-TRANSIENT RESPONSE
VCC
5V/div
VOUT
1V/div
VRS+ = 20V
VCC = 20V STEP
VREF1 = VREF2 = 2.5V
VCC = 40V
VCC = 20V
MAX4080 toc30
VCC
(0 TO 10V)
5V/div
OUTPUT
2.5V/div
100μs/div
MAX4080T
STARTUP DELAY
(VSENSE = 250mV)
Detailed Description
The MAX4080/MAX4081 unidirectional and bidirectional
high-side, current-sense amplifiers feature a 4.5V to
76V input common-mode range that is independent of
supply voltage. This feature allows the monitoring of
current out of a battery as low as 4.5V and also enables
high-side current sensing at voltages greater than the
supply voltage (VCC). The MAX4080/MAX4081 monitors
current through a current-sense resistor and amplifies
the voltage across the resistor. The MAX4080 senses
current unidirectionally, while the MAX4081 senses cur-
rent bidirectionally.
The 76V input voltage range of the MAX4080/MAX4081
applies independently to both supply voltage (VCC)
and common-mode, input-sense voltage (VRS+). High-
side current monitoring does not interfere with the
ground path of the load being measured, making the
MAX4080/MAX4081 particularly useful in a wide range
of high-voltage systems.
Battery-powered systems require a precise bidirectional
current-sense amplifier to accurately monitor the bat-
tery’s charge and discharge. The MAX4081 charging
current is represented by an output voltage from VREF
to VCC, while discharge current is given from VREF to
GND. Measurements of OUT with respect to VREF yield
a positive and negative voltage during charge and dis-
charge, as illustrated in Figure 1 for the MAX4081T.
Current Monitoring
The MAX4080 operates as follows: current from the
source flows through RSENSE to the load (Figure 2), cre-
ating a sense voltage, VSENSE. Since the internal-sense
amplifier’s inverting input has high impedance, negligible
current flows through RG2 (neglecting the input bias
current). Therefore, the sense amplifier’s inverting input
voltage equals VSOURCE - (ILOAD)(RSENSE). The ampli-
fier’s open-loop gain forces its noninverting input to the
same voltage as the inverting input. Therefore, the drop
across RG1 equals VSENSE. The internal current mirror
multiplies IRG1 by a current gain factor, β, to give IA2 =
β✕IRG1. Amplifier A2 is used to convert the output
current to a voltage and then sent through amplifier A3.
Total gain = 5V/V for MAX4080F, 20V/V for the
MAX4080T, and 60V/V for the MAX4080S.
The MAX4081 input stage differs slightly from the
MAX4080 (Figure 3). Its topology allows for monitoring
of bidirectional currents through the sense resistor.
When current flows from RS+ to RS-, the MAX4081
matches the voltage drop across the external sense
resistor, RSENSE, by increasing the current through the
Q1 and RG1. In this way, the voltages at the input ter-
minals of the internal amplifier A1 are kept constant and
an accurate measurement of the sense voltage is
achieved. In the following amplifier stages of the
MAX4081, the output signal of amplifier A2 is level-
shifted to the reference voltage (VREF = VREF1A =
VREF1B), resulting in a voltage at the output pin (OUT)
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
_______________________________________________________________________________________ 9
Pin Description
PIN
MAX4080 MAX4081 NAME FUNCTION
1 1 RS+ Power connection to the external-sense resistor.
22 V
CC Supply Voltage Input. Decouple VCC to GND with at least a 0.1µF capacitor to
bypass line transients.
3, 6, 7 3 N.C. No Connection. No internal connection. Leave open or connect to ground.
4 4 GND Ground
5 5 OUT
Voltage Output. For the unidirectional MAX4080, VOUT is proportional to
VSENSE. For the bidirectional MAX4081, the difference voltage (VOUT - VREF) is
proportional to VSENSE and indicates the correct polarity.
8 8 RS- Load connection to the external sense resistor.
— 6 REF1B Reference Voltage Input: Connect REF1B to REF1A or to GND (see the External
Reference section).
— 7 REF1A
Reference Voltage Input: Connect REF1A and REF1B to a fixed reference
voltage (VREF). VOUT is equal to VREF when VSENSE is zero (see the External
Reference section).
MAX4080/MAX4081
that swings above VREF voltage for positive-sense volt-
ages and below VREF for negative-sense voltages.
VOUT is equal to VREF when VSENSE is equal to zero.
Set the full-scale output range by selecting RSENSE and
the appropriate gain version of the MAX4080/
MAX4081.
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
10 ______________________________________________________________________________________
MAX4081T
VSENSE ICHARGE
ILOAD
RSENSE
VCC
GND
RS+RS-
OUT
REF1A
REF1B
5V
SYSTEM LOAD
AND CHARGER
BATTERY
VOUT = GND
VOUT = 10V
VREF1A = VREF1B = 5V
DISCHARGE CURRENT
4.5V TO 76V
V
OUT
- V
REF
CHARGE CURRENT
5V
10V
-250mV 250mV
-5V
VSENSE
Figure 1. MAX4081T OUT Transfer Curve
RSENSE
VSENSE
ILOAD
OUT
RG1 RG2
RS-
Q1
RS+
CURRENT
MIRROR
A1
IA2
A3A2
MAX4080
VSENSE
RG1 RG2
VREF
RS-
REF1B
OUT
GND
REF1A
Q1 Q2
RF
125kΩ
125kΩ
RS+
CURRENT
MIRROR
CURRENT
MIRROR
A1
A2
MAX4081
Figure 3. MAX4081 Functional Diagram
Figure 2. MAX4080 Functional Diagram
Note: For Gain = 5 (F), RG1 = RG2 = 160k.
For Gain = 20 (T), RG1 = RG2 = 60k.
For Gain = 60 (S), RG1 = RG2 = 20k
.
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
______________________________________________________________________________________ 11
Table 1. Typical Component Values
FULL-SCALE LOAD
CURRENT, ILOAD (A)
CURRENT-SENSE
RESISTOR (mΩ)
GAIN
(V/V)
FULL-SCALE
VSENSE
(mV)
MAX4081 FULL-SCALE
OUTPUT VOLTAGE
(VOUT - VREF, V)
0.500 1000 5 ±500 ±2.5
0.125 1000 20 ±125 ±2.5
0.050 1000 60 ±50 ±3.0
5.000 100 5 ±500 ±2.5
1.250 100 20 ±125 ±2.5
0.500 100 60 ±50 ±3.0
50.000 10 5 ±500 ±2.5
12.500 10 20 ±125 ±2.5
5.000 10 60 ±50 ±3.0
FULL-SCALE LOAD
CURRENT, ILOAD (A)
CURRENT-SENSE
RESISTOR (mΩ)
GAIN
(V/V)
FULL-SCALE
VSENSE
(mV)
MAX4080 FULL-SCALE
OUTPUT VOLTAGE (V)
1.000 1000 5 1000 5.0
0.250 1000 20 250 5.0
0.100 1000 60 100 6.0
10.000 100 5 1000 5.0
2.500 100 20 250 5.0
1.000 100 60 100 6.0
50.000 10 5 500 2.5
25.000 10 20 250 5.0
10.000 10 60 100 6.0
External References (MAX4081)
For the bidirectional MAX4081, the VOUT reference level
is controlled by REF1A and REF1B. VREF is defined as
the average voltage of VREF1A and VREF1B. Connect
REF1A and REF1B to a low-noise, regulated voltage
source to set the output reference level. In this mode,
VOUT equals VREF1A when VSENSE equals zero (see
Figure 4).
Alternatively, connect REF1B to ground, and REF1A to a
low-noise, regulated voltage source. In this case, the out-
put reference level (VREF) is equal to VREF1A divided by
two. VOUT equals VREF1A/2 when VSENSE equals zero.
In either mode, the output swings above the reference
voltage for positive current-sensing (VRS+ > VRS-). The
output swings below the reference voltage for negative
current-sensing (VRS+ < VRS-).
Applications Information
Recommended Component Values
Ideally, the maximum load current develops the full-
scale sense voltage across the current-sense resistor.
Choose the gain needed to yield the maximum output
voltage required for the application:
VOUT = VSENSE ✕AV
where VSENSE is the full-scale sense voltage, 1000mV
for gain of 5V/V, 250mV for gain of 20V/V, 100mV for
gain of 60V/V, and AVis the gain of the device.
In applications monitoring a high current, ensure that
RSENSE is able to dissipate its own I2R loss. If the resis-
tor’s power dissipation is exceeded, its value may drift
or it may fail altogether.
The MAX4080/MAX4081 sense a wide variety of cur-
rents with different sense-resistor values. Table 1 lists
common resistor values for typical operation.
MAX4080/MAX4081
The full-scale output voltage is VOUT = RSENSE ✕ILOAD
(MAX) ✕AV, for the MAX4080 and VOUT = VREF ±
RSENSE ✕ ILOAD(MAX) ✕ AVfor the MAX4081.
VSENSE(MAX) is 1000mV for the 5V/V gain version,
250mV for the 20V/V gain version, and 100mV for the
60V/V gain version.
Choosing the Sense Resistor
Choose RSENSE based on the following criteria:
•Voltage Loss: A high RSENSE value causes the
power-source voltage to degrade through IR loss. For
minimal voltage loss, use the lowest RSENSE value.
•Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately. This is due to
offsets becoming less significant when the sense
voltage is larger. For best performance, select
RSENSE to provide approximately 1000mV (gain of
5V/V), 250mV (gain of 20V/V), or 100mV (gain of
60V/V) of sense voltage for the full-scale current in
each application.
•Efficiency and Power Dissipation: At high current
levels, the I2R losses in RSENSE can be significant.
Take this into consideration when choosing the
resistor value and its power dissipation (wattage)
rating. Also, the sense resistor’s value might drift if it
is allowed to heat up excessively.
•Inductance: Keep inductance low if ISENSE has a
large high-frequency component. Wire-wound resis-
tors have the highest inductance, while metal film is
somewhat better. Low-inductance, metal-film resis-
tors are also available. Instead of being spiral-
wrapped around a core, as in metal-film or wire-
wound resistors, they are a straight band of metal
and are available in values under 1Ω.
Because of the high currents that flow through RSENSE,
take care to eliminate parasitic trace resistance from
causing errors in the sense voltage. Either use a four-
terminal current-sense resistor or use Kelvin (force and
sense) PC board layout techniques.
Dynamic Range Consideration
Although the MAX4081 have fully symmetrical bidirec-
tional VSENSE input capability, the output voltage range
is usually higher from REF to VCC and lower from REF
to GND (unless the supply voltage is at the lowest end
of the operating range). Therefore, the user must con-
sider the dynamic range of current monitored in both
directions and choose the supply voltage and the refer-
ence voltage (REF) to make sure the output swing
above and below REF is adequate to handle the swings
without clipping or running out of headroom.
Power-Supply Bypassing and Grounding
For most applications, bypass VCC to GND with a 0.1µF
ceramic capacitor. In many applications, VCC can be
connected to one of the current monitor terminals (RS+
or RS-). Because VCC is independent of the monitored
voltage, VCC can be connected to a separate regulated
supply.
If VCC will be subject to fast-line transients, a series
resistor can be added to the power-supply line of the
MAX4080/MAX4081 to minimize output disturbance.
This resistance and the decoupling capacitor reduce
the rise time of the transient. For most applications, 1kΩ
in conjunction with a 0.1µF bypass capacitor work well.
The MAX4080/MAX4081 require no special considera-
tions with respect to layout or grounding. Consideration
should be given to minimizing errors due to the large
charge and discharge currents in the system.
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
12 ______________________________________________________________________________________
MAX4081
RSENSE
ILOAD = 0
LOAD
VCC
GND
RS-RS+
OUT
REF1A
REF1B
5V
5V
10V
MAX4081
RSENSE
ILOAD = 0
LOAD
VCC
GND
RS-RS+
OUT
REF1A
REF1B
5V
Figure 4. MAX4081 Reference Inputs
Power Management
The bidirectional capability of the MAX4081 makes it an
excellent candidate for use in smart battery packs. In
the application diagram (Figure 5), the MAX4081 moni-
tors the charging current into the battery as well as the
discharge current out of the battery. The microcon-
troller stores this information, allowing the system to
query the battery's status as needed to make system
power-management decisions.
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
______________________________________________________________________________________ 13
MAX4080
VCC = 4.5V TO 76V
RSENSE
ISENSE
SYSTEM
LOAD
VCC
GND
RS-RS+
OUT
Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 185
PROCESS: Bipolar
Selector Guide
MAX4081
RSENSE
VCC
GND
RS-RS+
OUT
REF1A
REF1B
SYSTEM
POWER
MANAGEMENT
AND
CHARGER
CIRCUITRY
μC
1.8V
SERIAL
INTERFACE
BATTERY
MAX1243
ADC
Figure 5. MAX4081 Used In Smart-Battery Application
PART GAIN (V/V) ISENSE
MAX4080FAUA 5 Unidirectional
MAX4080FASA 5 Unidirectional
MAX4080TAUA 20 Unidirectional
MAX4080TASA 20 Unidirectional
MAX4080SAUA 60 Unidirectional
MAX4080SASA 60 Unidirectional
MAX4081FAUA 5 Bidirectional
MAX4081FASA 5 Bidirectional
MAX4081TAUA 20 Bidirectional
MAX4081TASA 20 Bidirectional
MAX4081SAUA 60 Bidirectional
MAX4081SASA 60 Bidirectional
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
14 ______________________________________________________________________________________
8LUMAXD.EPS
α
α
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
8 µMAX U8-2 21-0036
8 SO S8-2 21-0041
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
______________________________________________________________________________________ 15
SOICN .EPS
PACKAGE OUTLINE, .150" SOIC
1
1
21-0041 B
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
MAX
0.010
0.069
0.019
0.157
0.010
INCHES
0.150
0.007
E
C
DIM
0.014
0.004
B
A1
MIN
0.053A
0.19
3.80 4.00
0.25
MILLIMETERS
0.10
0.35
1.35
MIN
0.49
0.25
MAX
1.75
0.050
0.016L0.40 1.27
0.3940.386D
D
MINDIM
D
INCHES
MAX
9.80 10.00
MILLIMETERS
MIN MAX
16 AC
0.337 0.344 AB8.758.55 14
0.189 0.197 AA5.004.80 8
N MS012
N
SIDE VIEW
H 0.2440.228 5.80 6.20
e 0.050 BSC 1.27 BSC
C
HE
eBA1
A
D
0∞-8∞
L
1
VARIATIONS:
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
MAX4080/MAX4081
76V, High-Side, Current-Sense Amplifiers with
Voltage Output
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.
16
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 10/02 Initial release —
1 11/08 Added values for RG1 and RG2 10