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MAX4172

Low-Cost, Precision, High-Side

Current-Sense Amplifier

_______________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 0 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

o Low-Cost, High-Side Current-Sense Amplifier

o ±0.5% Typical Full-Scale Accuracy Over

Temperature

o 3V to 32V Supply Operation

o High Accuracy +2V to +32V Common-Mode

Range, Functional Down to 0V, Independent of

Supply Voltage

o 800kHz Bandwidth [V

SENSE

= 100mV (1C)]

200kHz Bandwidth [V

SENSE

= 6.25mV (C/16)]

o Available in Space-Saving µMAX and SO

Packages

OUT

GND

FEEDBACK LOOP

LOW-COST BATTERY CHARGER/CURRENT SOURCE

OUT

= 500mV/A

OUT

1kΩ

100kΩ

ANALOG OR

LOGIC SUPPLY

0 TO 32V

OUT

SENSE

/ 100Ω

V+

RS+

SENSE

50mΩ

SENSE

RS-

MAX4172

POWER GOOD

LOAD/

BATTERY

LOW-COST

SWITCHING

REGULATOR

UNREGULATED

DC SUPPLY

3V TO 32V

__________________Pin Configuration

TOP VIEW

OUT

GND

N.C.

V+

RS-

N.C.

RS+

µMAX/SO

MAX4172

__________Typical Operating Circuit

19-1184; Rev 2; 10/12

PART

MAX4172ESA+

MAX4172EUA+ -40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 SO

8 µMAX

______________Ordering Information

Denotes a lead(Pb)-free/RoHS-compliant package.

µMAX is a registered trademark of Maxim Integrated Products, Inc.

Summary of content (9 pages)

PAGE 1
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier _______________General Description The MAX4172 is a low-cost, precision, high-side currentsense amplifier for portable PCs, telephones, and other systems where battery/DC power-line monitoring is critical. High-side power-line monitoring is especially useful in battery-powered systems, since it does not interfere with the battery charger’s ground path.
PAGE 2
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ABSOLUTE MAXIMUM RATINGS 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) ....................
PAGE 3
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ELECTRICAL CHARACTERISTICS (continued) (V+ = +3V to +32V; VRS+, VRS- = 0 to 32V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at V+ = +12V, VRS+ = 12V, TA = +25°C.) PARAMETER SYMBOL CONDITIONS Maximum Output Voltage (OUT) MIN TYP MAX IOUT ≤ 1.5mA Bandwidth Maximum Output Current V+ - 1.2 VSENSE = 100mV 800 VSENSE = 6.25mV (Note 1) 200 IOUT Transconductance Gm = IOUT/(VRS+ - VRS-), VSENSE = 100mV, VRS+ > 2.
PAGE 4
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ____________________________Typical Operating Characteristics (continued) (V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA = +25°C, unless otherwise noted.) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY ERROR vs. SENSE VOLTAGE MAX4172-05 35 MAX4172-04 40 35 VSENSE = 100mV 30 30 25 ERROR (%) ERROR (%) 25 20 15 20 0.5VP-P 15 10 1.0VP-P 10 5 5mVP-P 5 0 0 -5 0.1m 1m 10m 100m 0.01 1 0.
PAGE 5
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ____________________________Typical Operating Characteristics (continued) (V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA = +25°C, unless otherwise noted.
PAGE 6
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier 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 R G1 combine to result in the MAX4172 transconductance (G m ) of 10mA/V. G m is defined as being equal to IOUT/(VRS+ - VRS-).
PAGE 7
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Table 1. Suggested Component Values FULL-SCALE LOAD CURRENT (A) CURRENT-SENSE RESISTOR, RSENSE (mΩ) OUTPUT RESISTOR, ROUT (kΩ) FULL-SCALE OUTPUT VOLTAGE, VOUT (V) SCALE FACTOR, VOUT/ISENSE (V/A) 0.1 1000 3.48 3.48 34.8 1 100 3.48 3.48 3.48 5 20 3.48 3.48 0.696 10 10 3.48 3.48 0.348 • Accuracy: A high RSENSE value allows lower currents to be measured more accurately.
PAGE 8
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Power-Supply Bypassing and Grounding In most applications, grounding the MAX4172 requires no special precautions. However, in high-current systems, 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 currentmeasurement accuracy. The MAX4172 requires no special bypassing and responds quickly to transient changes in line current.
PAGE 9
MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Revision History REVISION NUMBER REVISION DATE 0 12/96 Initial release 1 6/10 Clarified 0 to 2V is not a high-accuracy range for the device, removed future product reference, added lead-free options and soldering temperature. 2 10/12 Revised the Package Information.