_______________General Description
The MAX4172 is a low-cost, precision, high-side current-
sense amplifier for portable PCs, telephones, and other
systems where battery/DC power-line monitoring is criti-
cal. High-side power-line monitoring is especially useful in
battery-powered systems, since it does not interfere with
the battery charger’s ground path. Wide bandwidth and
ground-sensing capability make the MAX4172 suitable
for closed-loop battery-charger and general-purpose cur-
rent-source applications. The 0V to 32V input common-
mode range is independent of the supply voltage, which
ensures that current-sense feedback remains viable,
even when connected to a battery in deep discharge.
To provide a high level of flexibility, the MAX4172 func-
tions with an external sense resistor to set the range of
load current to be monitored. It has a current output that
can be converted to a ground-referred voltage with a sin-
gle resistor, accommodating a wide range of battery volt-
ages and currents.
An open-collector power-good output (PG) indicates
when the supply voltage reaches an adequate level to
guarantee proper operation of the current-sense amplifi-
er. The MAX4172 operates with a 3.0V to 32V supply
voltage, and is available in a space-saving, 8-pin µMAX®
or SO package.
________________________Applications
Portable PCs: Notebooks/Subnotebooks/Palmtops
Battery-Powered/Portable Equipment
Closed-Loop Battery Chargers/Current Sources
Smart-Battery Packs
Portable/Cellular Phones
Portable Test/Measurement Systems
Energy Management Systems
____________________________Features
♦Low-Cost, High-Side Current-Sense Amplifier
♦±0.5% Typical Full-Scale Accuracy Over
Temperature
♦3V to 32V Supply Operation
♦High Accuracy +2V to +32V Common-Mode
Range, Functional Down to 0V, Independent of
Supply Voltage
♦800kHz Bandwidth [VSENSE = 100mV (1C)]
200kHz Bandwidth [VSENSE = 6.25mV (C/16)]
♦Available in Space-Saving µMAX and SO
Packages
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
________________________________________________________________
Maxim Integrated Products
1
OUT
GND
FEEDBACK LOOP
LOW-COST BATTERY CHARGER/CURRENT SOURCE
VOUT = 500mV/A
ROUT
1k
100k
ANALOG OR
LOGIC SUPPLY
2A
0V TO 32V
IOUT =
VSENSE / 100Ω
V+
RS+
RSENSE
50mΩ
VSENSE
RS-
PG
MAX4172
POWER GOOD LOAD/
BATTERY
LOW-COST
SWITCHING
REGULATOR
UNREGULATED
DC SUPPLY
3V TO 32V
__________________Pin Configuration
TOP VIEW
OUT
GND
N.C.
1
+
2
8
7
V+
PG
RS-
N.C.
RS+
µMAX/SO
3
4
6
5
MAX4172
__________Typical Operating Circuit
19-1184; Rev 1; 6/10
PART
MAX4172ESA+
MAX4172EUA+ -40°C to +85°C
-40°C to +85°C
TEMP. RANGE PIN-PACKAGE
8 SO
8 µMAX
______________Ordering Information
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.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
TA= 0°C to +85°C
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = +3V to +32V; VRS+, VRS- = 0V to 32V; TA= TMIN to TMAX; unless otherwise noted. Typical values are at V+ = +12V, VRS+ =
12V, 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.
V+, RS+, RS-, PG ...................................................-0.3V to +36V
OUT ..............................................................-0.3V to (V+ + 0.3V)
Differential Input Voltage, VRS+ - VRS-............................±700mV
Current into Any Pin..........................................................±50mA
Continuous Power Dissipation (TA= +70°C)
SO (derate 5.88mW/°C above +70°C)..........................471mW
µMAX (derate 4.10mW/°C above +70°C) .....................330mW
Operating Temperature Range
MAX4172E_A....................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
IOUT = 0mA
3V ≤V+ ≤32V, VRS+ > 2.0V
VSENSE = 100mV, V+ = 12V,
VRS+ = 12V
VSENSE = 6.25mV, V+ = 12V,
VRS+ = 12V (Note 1)
V+ = 12V, VRS+ = 12V
VRS+ ≤2.0V
2.0V < VRS+ < 32V
CONDITIONS
µA/V0.03∆IOUT / ∆VRS+
OUT Common-Mode
Rejection Ratio
mA0.8 1.6IV+
Supply Current
V032VRS-
V332V+Operating Voltage Range
Input Voltage Range
µA/V0.2∆IOUT / ∆V+
OUT Power-Supply
Rejection Ratio
±20
µA
±8.0
Low-Level Current Error
±0.1 ±0.75
4
mV150 175Maximum VSENSE Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
VRS+ > 2.0V, IOUT = 0mA
VRS+ ≤2.0V, IOUT = 0mA
0 27 42.5 µA
-325 42.5
IRS+
Positive Input Bias Current
VRS+ > 2.0V
VRS+ ≤2.0V
05085
µA
-650 85
IRS-
Negative Input Bias Current
MAX4172ESA,
TA= -40°C to 0°C
MAX4172ESA
MAX4172ESA
VOS
Input Offset Voltage mV
MAX4172EUA ±0.2 ±1.6
MAX4172EUA ±15
MAX4172EUA,
TA= -40°C to 0°C
±50
MAX4172EUA,
TA= 0°C to +85°C
µA
Output Current Error
±15
MAX4172ESA,
TA= 0°C to +85°C
±10
ELECTRICAL CHARACTERISTICS (continued)
(V+ = +3V to +32V; VRS+, VRS- = 0V to 32V; TA= TMIN to TMAX; unless otherwise noted. Typical values are at V+ = +12V, VRS+ =
12V, TA= +25°C.)
MAX4172
1000
950
500
010
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
600
650
550
900
850
800
MAX4172-01
V+ (V)
SUPPLY CURRENT (µA)
20 30
750
700
40
TA = +85°C
TA = +25°C
TA = -40°C
IOUT = 0mA
0.5
0.4
-0.5
010
OUTPUT ERROR
vs. SUPPLY VOLTAGE
-0.3
-0.4
-0.2
0.3
0.2
0.1
MAX4172-03
V+ (V)
ERROR (%)
20 30
0
-0.1
40
TA = +25°C
TA = +85°C
TA = -40°C
VSENSE = 100mV
1.5
1.0
-3.0
010
C/16 LOAD OUTPUT ERROR
vs. SUPPLY VOLTAGE
-2.0
-1.5
-2.5
0.5
0
MAX4172-02
V+ (V)
ERROR (%)
20 30
-0.5
-1.0
40
TA = +85°C
TA = +25°C
TA = -40°C
VSENSE = 6.25mV
__________________________________________Typical Operating Characteristics
(V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA= +25°C, unless otherwise noted.)
Low-Cost, Precision, High-Side
Current-Sense Amplifier
_______________________________________________________________________________________ 3
Note 1: 6.25mV = 1/16 of typical full-scale sense voltage (C/16).
Note 2: Valid operation of the MAX4172 is guaranteed by design when PG is low.
IOUT ≤1.5mA
CONDITIONS
VV+ - 1.2
Maximum Output Voltage
(OUT)
UNITSMIN TYP MAXSYMBOLPARAMETER
V+ = 2.5V, TA= +25°C
ISINK = 1.2mA, V+ = 2.9V, TA= +25°C
µA1
Leakage Current into PG
V0.4VOL
PG Output Low Voltage
VSENSE = 5mV to 100mV
VSENSE = 0mV to 100mV, 10% to 90%
µs
6
OUT Settling Time to 1% 1.3
ns400OUT Rise Time
VSENSE = 150mV MΩ20OUT Output Resistance
VSENSE = 100mV to 0mV, 90% to 10% ns800OUT Fall Time
Rising
Falling
V+ = 0V, VRS+ = VRS- = 32V µA0.1 1
Power-Off Input Leakage
Current (RS+, RS-)
VSENSE = 100mV kHz
800
Bandwidth
Gm= IOUT / (VRS+ - VRS-),
VSENSE = 100mV, VRS+ > 2.0V mA/V
9.8 10 10.2
Gm
Transconductance
mA1.5 1.75IOUT
Maximum Output Current
V+ rising V
2.77
V+ Threshold for PG Output
Low (Note 2)
VSENSE = 6.25mV (Note 1)
TA= 0°C to +85°C
V+ falling 2.67
TA= -40°C to 0°C
9.7 10 10.3
200
0.75
0.55
-0.65
06 3040
OUTPUT ERROR
vs. COMMON-MODE VOLTAGE
-0.45
-0.25
0.35
0.15
MAX4172-06
VRS- (V)
ERROR (%)
12 18
-0.05
24
TA = -40°C
TA = +25°C
VSENSE = 100mV
TA = +85°C
2.95
2.90
2.45
-40 -15 85
V+ THRESHOLD FOR PG OUTPUT LOW
vs. TEMPERATURE
2.50
2.55
2.60
2.85
2.80
2.75
2.70
MAX4172-07
TEMPERATURE (°C)
V+ TRIP THRESHOLD (V)
10 35
2.65
60
V+ RISING VOLTAGE
V+ FALLING VOLTAGE
40
-5
0.1m 10m 100m1m 1
ERROR vs. SENSE VOLTAGE
0
MAX4172-04
VSENSE (V)
ERROR (%)
10
5
15
20
25
30
35
35
0
0.01 0.1 1 10 100 1000
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
5
MAX4172-05
POWER-SUPPLY FREQUENCY (kHz)
ERROR (%)
15
10
20
30
25
5mVP-P
1.0VP-P
0.5VP-P
VSENSE = 100mV
10µs/div
0mV to 10mV VSENSE TRANSIENT RESPONSE
GND
VSENSE
5mV/div
VOUT
50mV/div
GND
MAX4172-08
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA= +25°C, unless otherwise noted.)
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
_______________________________________________________________________________________ 5
5µs/div
START-UP DELAY
GND
VOUT
5
00mV/div
V+
2V/div
GND
VSENSE = 100mV
MAX4172-10
10µs/div
V+ to PG POWER-UP DELAY
GND
PG
2V/div
V+
2V/div
GND
100kΩ PULL-UP RESISTOR FROM PG TO +4V
MAX4172-11
______________________________________________________________Pin Description
____________________________Typical Operating Characteristics (continued)
(V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA= +25°C, unless otherwise noted.)
Current Output. OUT is proportional to the magnitude of the sense voltage (VRS+ - VRS-). A 1kΩ
resistor from OUT to ground will result in a voltage equal to 10V/V of sense voltage.
OUT6
Power Good Open-Collector Logic Output. A low level indicates that V+ is sufficient to power the
MAX4172, and adequate time has passed for power-on transients to settle out.
PG
7
Supply Voltage Input for the MAX4172V+8
GroundGND5
No Connect. No internal connection. Leave open or connect to GND.N.C.3, 4
PIN
Load-side connection for the external sense resistor. The “-” indicates the direction of current flow.RS-2
Power connection to the external sense resistor. The “+” indicates the direction of current flow.RS+1
FUNCTIONNAME
_______________Detailed Description
The MAX4172 is a unidirectional, high-side current-sense
amplifier with an input common-mode range that is inde-
pendent of supply voltage. This feature not only allows
the monitoring of current flow into a battery in deep dis-
charge, but also enables high-side current sensing at
voltages far in excess of the supply voltage (V+).
The MAX4172 current-sense amplifier’s unique topolo-
gy simplifies current monitoring and control. The
MAX4172’s amplifier operates as shown in Figure 1.
The battery/load current flows through the external
sense resistor (RSENSE), from the RS+ node to the RS-
node. Current flows through RG1 and Q1, and into the
current mirror, where it is multiplied by a factor of 50
before appearing at OUT.
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. Since A1’s inverting input is
high impedance, no current flows though RG2 (neglect-
ing the input bias current), so A1’s negative input is
equal to VSOURCE - (ILOAD x RSENSE). A1’s open-loop
gain forces its positive input to essentially the same
voltage level as the negative input. Therefore, the drop
across RG1 equals ILOAD x RSENSE. Then, since IRG1
MAX4172
flows through RG1, IRG1 x RG1 = ILOAD x RSENSE. The
internal current mirror multiplies IRG1 by a factor of 50
to give IOUT = 50 x IRG1. Substituting IOUT / 50 for IRG1,
(IOUT / 50) x RG1 = ILOAD x RSENSE, or:
IOUT = 50 x ILOAD x (RSENSE / RG1)
The internal current gain of 50 and the factory-trimmed
resistor RG1 combine to result in the MAX4172
transconductance (Gm) of 10mA/V. Gmis de-
fined as being equal to IOUT / (VRS+ - VRS-). Since
(VRS+ - VRS-) = ILOAD x RSENSE, the output current
(IOUT) can be calculated with the following formula:
IOUT = Gmx (VRS+ - VRS-) =
(10mA/V) x (ILOAD x RSENSE)
Current Output
The output voltage equation for the MAX4172 is given
below:
VOUT = (Gm) x (RSENSE x ROUT x ILOAD)
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 Gm= MAX4172 transconductance
(10mA/V).
The full-scale output voltage range can be set by
changing the ROUT resistor value, but the output volt-
age must be no greater than V+ - 1.2V. 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 that can be
integrated by connecting it to a capacitive load.
PG
Output
The PG output is an open-collector logic output that
indicates the status of the MAX4172’s V+ power sup-
ply. A logic low on the PG output indicates that V+ is
sufficient to power the MAX4172. This level is tempera-
ture dependent (see
Typical Operating Characteristics
graphs), and is typically 2.7V at room temperature. The
internal PG comparator has a 100mV (typical) hystere-
sis to prevent possible oscillations caused by repeated
toggling of the PG output, making the device ideal for
power-management systems lacking soft-start capabili-
ty. An internal delay (15µs typical) in the PG compara-
tor allows adequate time for power-on transients to
settle out. The PG status indicator greatly simplifies the
design of closed-loop systems by ensuring that the
components in the control loop have sufficient voltage
to operate correctly.
__________Applications Information
Suggested Component Values
for Various Applications
The
Typical Operating Circuit
is useful in a wide variety
of applications. Table 1 shows suggested component
values and indicates the resulting scale factors for vari-
ous applications required to sense currents from
100mA to 10A.
Adjust the RSENSE value to monitor higher or lower cur-
rent levels. Select RSENSE using the guidelines and for-
mulas in the following section.
Sense Resistor, RSENSE
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.
Low-Cost, Precision, High-Side
Current-Sense Amplifier
6 _______________________________________________________________________________________
RG1
RS+
RSENSE
INPUT
RG2
TO LOAD/
BATTERY
RS-VSENSE
A1
1:50
CURRENT
MIRROR
MAX4172
OUT
VTH
IOUT = 50 IRG1
IRG1
Q1
V+
PG
V+
GND
ILOAD
Figure 1. Functional Diagram
•Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately. This is
because offsets become less significant when the
sense voltage is larger. For best performance,
select RSENSE to provide approximately 100mV 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.
•Cost: If the cost of RSENSE is an issue, you might
want to use an alternative solution, as shown in
Figure 2. This solution uses the PC board traces to
create a sense resistor. Because of the inaccura-
cies of the copper resistor, the full-scale current
value must be adjusted with a potentiometer. Also,
copper’s resistance temperature coefficient is fairly
high (approximately 0.4%/°C).
In Figure 2, assume that the load current to be mea-
sured is 10A, and that you have determined a 0.3-inch-
wide, 2-ounce copper to be appropriate. The resistivity
of 0.1-inch-wide, 2-ounce (70µm thickness) copper is
30mΩ/ft. For 10A, you might want RSENSE = 5mΩfor a
50mV drop at full scale. This resistor requires about 2
inches of 0.1-inch-wide copper trace.
Current-Sense Adjustment
(Resistor Range, Output Adjust)
Choose ROUT after selecting RSENSE. Choose ROUT to
obtain the full-scale voltage you require, given the full-
scale IOUT determined by RSENSE. OUT’s high imped-
ance permits using ROUT values up to 200kΩwith
minimal error. OUT’s load impedance (e.g., the input of
an op amp or ADC) must be much greater than ROUT
(e.g., 100 x ROUT) to avoid degrading measurement
accuracy.
High-Current Measurement
The MAX4172 can achieve high-current measurements
by using low-value sense resistors, which can be paral-
leled to further increase the current-sense limit. As an
alternative, PC board traces can be adjusted over a
wide range.
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
_______________________________________________________________________________________ 7
3.48 3.48 3.481001
3.48
3.48
OUTPUT
RESISTOR, ROUT
(kΩ)
3.48 0.3481010
3.48 3.48
3.48
FULL-SCALE
OUTPUT
VOLTAGE, VOUT (V)
0.696205
34.8
FULL-SCALE
LOAD CURRENT
(A)
SCALE FACTOR,
VOUT/ISENSE (V/A)
10000.1
CURRENT-SENSE
RESISTOR,
RSENSE (mΩ)
Table 1. Suggested Component Values
OUT
GND
1
O.1 in. COPPER
VSENSE
RSENSE
INPUT LOAD/BATTERY
VSUPPLY
ROUT
O.3 in. COPPER O.3 in. COPPER
2
8
RS+
RS-
V+ 3V TO 32V
MAX4172
6
5
Figure 2. MAX4172 Connections Showing Use of PC Board
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
8 _______________________________________________________________________________________
___________________Chip Information
Power-Supply Bypassing and Grounding
In most applications, grounding the MAX4172 requires
no special precautions. However, in high-current sys-
tems, large voltage drops can develop across the
ground plane, which can add to or subtract from VOUT.
Use a single-point star ground for the highest current-
measurement accuracy.
The MAX4172 requires no special bypassing and
responds quickly to transient changes in line current. If
the noise at OUT caused by these transients is a prob-
lem, you can place a 1µF capacitor at the OUT pin to
ground. You can also place a large capacitor at the RS
terminal (or load side of the MAX4172) to decouple the
load, reducing the current transients. These capacitors
are not required for MAX4172 operation or stability. The
RS+ and RS- inputs can be filtered by placing a capac-
itor (e.g., 1µF) between them to average the sensed
current.
SUBSTRATE CONNECTED TO GND
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 OUTLINE NO. LAND
PATTERN NO.
SO S8+4 21-0042 90-0096
µMAX U8+1 21-0036 90-0092
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 _____________________
9
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX4172
Low-Cost, Precision, High-Side
Current-Sense Amplifier
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 12/96 Initial release —
1 6/10 Clarified 0V to 2V is not a high-accuracy range for the device, removed future
product reference, added lead-free options and soldering temperature 1, 2