_______________General Description
The MAX471/MAX472 are complete, bidirectional, high-
side current-sense amplifiers for portable PCs, tele-
phones, and other systems where battery/DC
power-line monitoring is critical. High-side power-line
monitoring is especially useful in battery-powered sys-
tems, since it does not interfere with the ground paths
of the battery chargers or monitors often found in
“smart” batteries.
The MAX471 has an internal 35mΩ current-sense resis-
tor and measures battery currents up to ±3A. For appli-
cations requiring higher current or increased flexibility,
the MAX472 functions with external sense and gain-set-
ting resistors. Both devices have a current output that
can be converted to a ground-referred voltage with a
single resistor, allowing a wide range of battery volt-
ages and currents.
An open-collector SIGN output indicates current-flow
direction, so the user can monitor whether a battery is
being charged or discharged. Both devices operate
from 3V to 36V, draw less than 100µA over tempera-
ture, and include a 5µA max shutdown mode.
________________________Applications
Portable PCs:
Notebooks/Subnotebooks/Palmtops
Smart Battery Packs
Cellular Phones
Portable Phones
Portable Test/Measurement Systems
Battery-Operated Systems
Energy Management Systems
____________________________Features
' Complete High-Side Current Sensing
' Precision Internal Sense Resistor (MAX471)
' 2% Accuracy Over Temperature
' Monitors Both Charge and Discharge
' 3A Sense Capability with Internal Sense Resistor
(MAX471)
' Higher Current-Sense Capability with External
Sense Resistor (MAX472)
' 100µA Max Supply Current
' 5µA Max Shutdown Mode
' 3V to 36V Supply Operation
' 8-Pin DIP/SO Packages
______________Ordering Information
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________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
8
7
6
5
OUT
RS-
RS-
SIGNGND
RS+
RS+
SHDN
MAX471
DIP/SO
TOP VIEW
_________________Pin Configurations
MAX471
RS+
RS+ RS-
RS-
SIGN
OUT
GNDSHDN
3V
TO
36V
100k
ILOAD
2000
2k
ILOAD TO
LOAD or CHARGER
LOGIC
SUPPLY
DISCHARGE/CHARGE
VOUT (1V/A)
__________Typical Operating Circuit
19-0335; Rev 1; 5/96
PART
MAX471CPA
MAX471CSA
MAX471EPA -40°C to +85°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 SO
8 Plastic DIP
MAX471ESA -40°C to +85°C 8 SO
MAX472CPA 0°C to +70°C 8 Plastic DIP
MAX472CSA 0°C to +70°C 8 SO
MAX472EPA -40°C to +85°C 8 Plastic DIP
MAX472ESA -40°C to +85°C 8 SO
MAX472 Pin Configuration continued on last page.
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
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2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS—MAX471
(RS+ = +3V to +36V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°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.
Supply Voltage, RS+, RS-, VCC to GND....................-0.3V, +40V
RMS Current, RS+ to RS- (MAX471 only)..........................±3.3A
Peak Current, (RS+ to RS-) ......................................see Figure 5
Differential Input Voltage, RG1 to RG2 (MAX472 only) .....±0.3V
Voltage at Any Pin Except SIGN
MAX471 only ...........................................-0.3V to (RS+ - 0.3V)
MAX472 only ..........................................-0.3V to (VCC + 0.3V)
Voltage at SIGN......................................................-0.3V to +40V
Current into SHDN, GND, OUT, RG1, RG2, VCC................±50mA
Current into SIGN.................................................+10mA, -50mA
Continuous Power Dissipation (TA = +70°C)
MAX471 (Note 1):
Plastic DIP (derate 17.5mW/°C above +70°C) ..................1.4W
SO (derate 9.9mW/°C above +70°C).............................791mW
MAX472 :
Plastic DIP (derate 9.09mW/°C above +70°C) ..............727mW
SO (derate 5.88mW/°C above +70°C)...........................471mW
Operating Temperature Ranges
MAX47_C_A........................................................0°C to +70°C
MAX47_E_A .....................................................-40°C to +85°C
Junction Temperature Range ............................-60°C to +150°C
Storage Temperature Range .............................-60°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
VSHDN = 2.4V
ILOAD = 0A, excludes ISIGN
VSHDN = 0V
VSHDN = 2.4V
VSIGN = 0.3V
VSIGN = 36V
ILOAD = 30mA,
RS+ = 10V
MAX471E
MAX471C
ILOAD = 0A,
RS+ = 10V
ILOAD = 1A,
RS+ = 10V
3V ≤ RS+ ≤ 36V, ILOAD = 1A
CONDITIONS
V0 VRS+ - 1.5VOUTOUT Output Voltage Range
µA1.0IIHSHDN Input High Current
V2.4VIHSHDN Input High Voltage
µA1.0IILSHDN Input Low Current
V0.3VILSHDN Input Low Voltage
µA1.5 5.0IRS+(SHDN)Shutdown Supply Current
mA0.1IOLSIGN Sink Current
µA1.0SIGN Output Leakage Current
mA
±4.0 ±6.0SIGN Threshold (ILOAD required
to switch SIGN)
%/V0.1PSRRPower-Supply Rejection Ratio
ARMS±3ILOADSense Current
V
50 100IRS+
3 36VRS+Supply Voltage
Supply Current
µA
±3.0
Low-Level OUT Error
±2.5
µA
3.0
No-Load OUT Error
mΩ35 70RSENSESense Resistor
0.490 0.500 0.510
mA/A
0.4875 0.500 0.5125
IOUT/
ILOAD
Current-Sense Ratio
2.5
UNITSMIN TYP MAXSYMBOLPARAMETER
OUT Output Resistance ROUT ILOAD = 3.0A, VOUT = 0V to (VRS+ - 1.5V) 1 3 MΩ
OUT Rise, Fall Time tR, tF
ILOAD = 50mA to 3.0A, ROUT = 2kΩ,
COUT = 50pF, 10% to 90%
4 µs
OUT Settling Time to 1%
of Final Value
ts
ILOAD = 100mA to 3.0A, ROUT = 2kΩ,
COUT = 50pF
15 µs
MAX471C
MAX471C
MAX471C
MAX471E
MAX471E
MAX471E
±7.0
µA
Note 1: Due to special packaging considerations, MAX471 (DIP, SO) has a higher power dissipation rating than the MAX472. RS+
and RS- must be soldered to large copper traces to achieve this dissipation rating.
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_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS—MAX472
(VCC = +3V to +36V, RG1 = RG2 = 200Ω, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
Note 2: VOS is defined as the input voltage (VSENSE) required to give minimum IOUT.
Note 3: VSENSE is the voltage across the sense resistor.
VSHDN = 2.4V
MAX472C
VSHDN = 0V
ILOAD = 0A, excludes ISIGN
VSHDN = 2.4V
VSIGN = 0.3V
VSIGN = 36V
VCC = 10V,
VSENSE = 3mV
VCC = 10V
MAX472E
IRG1 - IGR2
3V ≤ VCC ≤ 36V, VSENSE = 100mV
CONDITIONS
V0 VCC - 1.5VOUTOUT Output Voltage Range
µA1.0IIHSHDN Input High Current
V2.4VIHSHDN Input High Voltage
µA1.0IILSHDN Input Low Current
V0.3VILSHDN Input Low Voltage
µA1.5 5.0ICC(SHDN)Shutdown Supply Current
mA0.1SIGN Output Sink Current
µA1.0SIGN Output Leakage Current
µV
60 140
SIGN Threshold (VSENSE
required to switch SIGN)
60 120
%/V0.1PSRRPower-Supply Rejection Ratio
120
µA20 35ICC
V3 36VCCSupply Voltage
Supply Current
µA
±3.0
Low-Level OUT Error
±2.5
µA
2.5
µV
140
VOS
Input Offset Voltage
(Note 2)
µA20 35IRG1, IRG2Input Bias Current
µA±0.4 ±3.0IOSInput Bias-Current Matching
UNITSMIN TYP MAXSYMBOLPARAMETER
OUT Output Resistance ROUT IOUT = 1.5mA 1 3 MΩ
OUT Rise, Fall Time tR, tF
VSENSE = 5mV to 150mV, ROUT = 2kΩ,
COUT = 50pF, 10% to 90%
4 µs
OUT Settling Time to 1%
of Final Value
ts
VSENSE = 5mV to 150mV, ROUT = 2kΩ,
COUT = 50pF
15 µs
Maximum Output Current IOUT 1.5 mA
MAX472C
MAX472E
MAX472C
MAX472E
VCC = 10V,
VSENSE = 0V 3
No-Load OUT Error
MAX472C
MAX472E
VSENSE = 100mV,
VCC = 10V (Note 3)
IRG/IOUTOUT Current Accuracy
MAX472C
%
±2
MAX472E ±2.5
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__________________________________________Typical Operating Characteristics
(Typical Operating Circuit (MAX471) or circuit of Figure 4, RG1 = RG2 = 200Ω, ROUT = 2kΩ (MAX472), TA = +25°C, unless
otherwise noted.)
65
35
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
40
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-0
1
VRS+ (V)
SU
PP
LY
C
UR
RE
NT
(µ
A)
21 2415 189 123 6 27 30 33 36
45
50
55
60
TA = +85°C
TA = +25°C
TA = -40°C
2.5
0
0.5
2.0
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-0
2
I S
HD
N
(µ
A) 1.5
1.0
SHUTDOWN CURRENT vs.
SUPPLY VOLTAGE
VRS+(V)
21 2415 189 123 6 27 30 33 36
TA = +85°C
TA = -40°C
TA = +25°C
4
-2
SIGN THRESHOLD vs.
SUPPLY VOLTAGE
-1
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SI
GN
T
HR
ES
HO
LD
(m
A)
21 2415 189 123 6 27 30 33 36
0
1
2
3
TA = +85°C
TA = +25°C
TA = -40°C
VRS+ (V)
0.6
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FS
ET
C
UR
RE
NT
(µ
A)
MAX471
NO-LOAD OFFSET CURRENT vs.
SUPPLY VOLTAGE
VRS+ (V)
21 2415 189 123 6 27 30 33 36
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
VS+ = VS-
TA = -40°C
TA = +85°C
TA = +25°C
28
-40 80
TEMPERATURE (°C)
RE
SI
ST
AN
CE
(m
Ω
)
20
30
-20 0 6040
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7
MAX471
RS+ TO RS- RESISTANCE vs.
TEMPERATURE
32
34
36
38
40
-12
0.01 0.10
MAX471
ERROR vs. LOAD CURRENT
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ILOAD (A)
ER
RO
R
(%
)
1 10
-15
-6
-9
-3
0
3
6
9
12
15
ILOAD FROM RS+ TO RS-
ILOAD FROM RS- TO RS+
40
0.01 10 1000
MAX471
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
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PS
RR
(%
)
1 100
35
30
25
20
15
10
5
0
0.10
V = 0mV TO 50mV
V = 0V TO 1V
V = 0V TO 0.5V
ILOAD = 1A
5V
RS+
OUT
GND
RS–
A
1µF
5ΩV
3.0
0
MAX472
NO-LOAD OUTPUT ERROR vs.
SUPPLY VOLTAGE
0.5
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VCC (V)
I O
UT
(µ
A)
21 2415 189 123 6 27 30 33 36
1.0
1.5
2.0
2.5
TA = +85°C
TA = -40°C
TA = +25°C
RG1 = RG2 = 0Ω
0.70
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R
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MAX472
ERROR vs. SUPPLY VOLTAGE
VCC (V)
21 2415 189 123 6 27 30 33 36
VRG1-VRG2 = 60mV,
RG1 = RG2 = 200Ω
0.80
0.90
1.00
1.10
TA = -40°C
TA = +25°C
TA = +85°C
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MAX472
ERROR vs. SENSE VOLTAGE
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VSENSE (mV)
ER
RO
R
(%
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15
5
0
-5
-15
1 100
VRG1-VRG2
VRG2-VRG1
1mA
10mA
100mA
1A
0.1
0
0.2
0.3
0.4
0.5
MAX471
NOISE vs. LOAD CURRENT
ISENSE
I O
UT
N
OI
SE
(µ
A R
M
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____________________________Typical Operating Characteristics (continued)
(Typical Operating Circuit (MAX471) or circuit of Figure 4, RG1 = RG2 = 200Ω, ROUT = 2kΩ (MAX472), TA = +25°C, unless
otherwise noted.)
100µs/div
VCC = 10V, ROUT = 2kΩ 1%, SIGN PULL-UP = 50kΩ 1%
LOAD
CURRENT
50mA/div
VOUT
50mV/div
MAX471
0mA to 100mA TRANSIENT RESPONSE
0A
10µs/div
ILOAD = 1A, ROUT = 2kΩ 1%
VOUT
500mV/div
MAX471
START-UP DELAY
VSHDN
5V/div
10µs/div
ROUT = 2kΩ 1%
ILOAD
1A/div
MAX471
0A TO 3A TRANSIENT RESPONSE
VOUT
10mV/div
100µs/div
VCC = 10V, ROUT = 2kΩ 1%, SIGN PULL-UP = 50kΩ 1%
LOAD
CURRENT
100mA/div
50mA/div50mA/div
VOUT
50mV/div
MAX471
-100mA to +100mA TRANSIENT RESPONSE
SIGN
50mV/div
0A
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_______________Detailed Description
The MAX471 and MAX472 current-sense amplifier’s
unique topology allows a simple design to accurately
monitor current flow. The MAX471/MAX472 contain two
amplifiers operating as shown in Figures 1 and 2. The
battery/load current flows from RS+ to RS- (or vice
versa) through RSENSE. Current flows through either
RG1 and Q1 or RG2 and Q2, depending on the sense-
resistor current direction. Internal circuitry, not shown in
Figures 1 and 2, prevents Q1 and Q2 from turning on at
the same time. The MAX472 is identical to the
MAX471, except that RSENSE and gain-setting resistors
RG1 and RG2 are external (Figure 2).
To analyze the circuit of Figure 1, assume that current
flows from RS+ to RS- and that OUT is connected to
GND through a resistor. In this case, amplifier A1 is
active and output current IOUT flows from the emitter of
Q1. Since no current flows through RG2 (Q2 is off), the
negative input of A1 is equal to VSOURCE - (ILOAD x
RSENSE). The open-loop gain of A1 forces its positive
input to essentially the same level as the negative input.
Therefore, the drop across RG1 equals ILOAD x
RSENSE. Then, since IOUT flows through Q1 and RG
(ignoring the extremely low base currents), IOUT x RG1
= ILOAD x RSENSE, or:
IOUT = (ILOAD x RSENSE) / RG1
Current Output
The output voltage equation for the MAX471/MAX472 is
given below. In the MAX471, the current-gain ratio has
been preset to 500µA/A so that an output resistor
(ROUT) of 2kΩ yields 1V/A for a full-scale value of +3V
at ±3A. Other full-scale voltages can be set with differ-
ent ROUT values, but the output voltage can be no
greater than VRS+ - 1.5V for the MAX471 or VRG_ - 1.5V
for the MAX472.
VOUT = (RSENSE x ROUT x ILOAD) / RG
where VOUT = the desired full-scale output voltage,
ILOAD = the full-scale current being sensed, RSENSE =
the current-sense resistor, ROUT = the voltage-setting
resistor, and RG = the gain-setting resistor (RG = RG1
= RG2).
The above equation can be modified to determine the
ROUT required for a particular full-scale range:
ROUT = (VOUT x RG) / (ILOAD x RSENSE)
For the MAX471, this reduces to:
ROUT = VOUT / (ILOAD x 500µA/A)
OUT is a high-impedance current-source output that
can be connected to other MAX471/MAX472 OUT pins
Precision, High-Side
Current-Sense Amplifiers
6 _______________________________________________________________________________________
______________________________________________________________Pin Description
Load side of the internal current-sense resistor. The “-” indicates direction of flow for SIGN
output only. Connect pins 6 and 7 together at the package.
RS-6, 7
Gain Resistor. Connect to load side of current-sense resistor through the gain resistor.RG2—
Power input for MAX472. Connect to sense resistor (RSENSE) junction with RG1.VCC—
Current output that is proportional to the magnitude of the sensed current flowing through
RSENSE. A 2kΩ resistor from this pin to ground will result in a voltage equal to 1V/Amp of
sensed current in the MAX471.
OUT8
Gain Resistor. Connect to battery side of current-sense resistor through the gain resistor.RG1—
Ground or Battery Negative TerminalGND4
An open-collector logic output. For the MAX471, a low level indicates current is flowing from
RS- to RS+. For the MAX472, a low level indicates a negative VSENSE (see Figure 2). SIGN is
high impedance when SHDN is high. Leave open if SIGN is not needed.
SIGN5
No Connect—no internal connectionN.C.—
Battery (or power) side of the internal current-sense resistor. The “+” indicates direction of
flow for SIGN output only. Connect pins 2 and 3 together at the package.
RS+2, 3
Shutdown. Connect to ground for normal operation. When high, supply current is
less than 5µA.
SHDN1
FUNCTION
MAX471
NAME
—
6
7
8
3
4
5
2
—
PIN
1
MAX472
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_______________________________________________________________________________________ 7
MAX471
Q2
8
5
OUT
SIGN
6, 7 RS-2, 3RS+
Q1
COMP
A2
RG2RG1
A1
RSENSE
MAX472
Q2
8
5
OUT
SIGN
TO LOAD/CHARGERPOWER SOURCE
OR
BATTERY
Q1
COMP
A2
RG2RG1
A1
RSENSE
3 6
VSENSE
VCC
7
Figure 1. MAX471 Functional Diagram
Figure 2. MAX472 Functional Diagram
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for current summing. A single scaling resistor is
required when summing OUT currents from multiple
devices (Figure 3). Current can be integrated by con-
necting OUT to a capacitive load.
SIGN Output
The current at OUT indicates magnitude. The SIGN out-
put indicates the current’s direction. Operation of the
SIGN comparator is straightforward. When Q1 (Figures
1 and 2) conducts, the output of A1 is high while A2’s
output is zero. Under this condition, a high SIGN output
indicates positive current flow (from RS+ to RS-). In bat-
tery-operated systems, this is useful for determining
whether the battery is charging or discharging. The
SIGN output may not correctly indicate if the load cur-
rent is such that IOUT is less than 3.5µA. The MAX471’s
SIGN output accurately indicates the direction of cur-
rent flow for load currents greater than 7mA.
SIGN is an open-collector output (sinks current only),
allowing easy interface with logic circuits powered from
any voltage. Connect a 100kΩ pull-up resistor from
SIGN to the logic supply. The convention chosen for
the polarity of the SIGN output ensures that it draws no
current when the battery is being discharged. If current
direction is not needed, float the SIGN pin.
Shutdown
When SHDN is high, the MAX471/MAX472 are shut
down and consume less than 5µA. In shutdown mode,
SIGN is high impedance and OUT turns off.
__________Applications Information
MAX471
The MAX471 obtains its power from the RS- pin. This
includes MAX471 current consumption in the total sys-
tem current measured by the MAX471. The small drop
across RSENSE does not affect the MAX471’s perfor-
mance.
Resistor Selection
Since OUT delivers a current, an external voltage gain-
setting resistor (ROUT to ground) is required at the OUT
pin in order to get a voltage. RSENSE is internal to the
MAX471. RG1 and RG2 are factory trimmed for an out-
put current ratio (output current to load current) of
500µA/A. Since they are manufactured of the same
material and in very close proximity on the chip, they
provide a high degree of temperature stability. Choose
ROUT for the desired full-scale output voltage up to RS-
- 1.5V (see the Current Output section).
Precision, High-Side
Current-Sense Amplifiers
8 _______________________________________________________________________________________
MAX471
RS+
RS+ RS-
RS-
SIGN
OUT
GND
TO LOAD/
CHARGER
3V
TO
36V
MAX471
RS+
RS+ RS-
RS-
SIGN
OUT
GND
1k
100k
LOGIC
SUPPLY
VOUT
3V
TO
36V
RSENSE
1
2
3
4
8
7
6
5
MAX472
RG2
100k
RG1
POWER
SOURCE
OR
BATTERY
TO LOAD/CHARGER
RG1
N.C.
SHDN
SIGN
OUT
VCC
GND
RG2
ROUT
LOGIC
SUPPLY
Figure 3. Paralleling MAX471s to Sense Higher Load Current Figure 4. MAX472 Standard Application Circuit
Peak Sense Current
The MAX471’s maximum sense current is 3ARMS. For
power-up, fault conditions, or other infrequent events,
larger peak currents are allowed, provided they are
short—that is, within a safe operating region, as shown
in Figure 5.
MAX472
RSENSE, RG1, and RG2 are externally connected on
the MAX472. VCC can be connected to either the
load/charge or power-source/battery side of the sense
resistor. Connect VCC to the load/charge side of
RSENSE if you want to include the MAX472 current drain
in the measured current.
Suggested Component Values
for Various Applications
The general circuit of Figure 4 is useful in a wide variety
of applications. It can be used for high-current applica-
tions (greater than 3A), and also for those where the full-
scale load current is less than the 3A of the MAX471.
Table 1 shows suggested component values and indi-
cates the resulting scale factors for various applications
required to sense currents from 100mA to 10A.
Higher or lower sense-current circuits can also be built.
Select components and calculate circuit errors using
the guidelines and formulas in the following section.
RSENSE
Choose RSENSE based on the following criteria:
a) Voltage Loss: A high RSENSE value will cause the
power-source voltage to d