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MAX4072ATA

Bidirectional, High-Side, Current-Sense Amplifiers with Reference

Maxim Integrated 

MAX4069–MAX4072

Bidirectional, High-Side, Current-Sense

Amplifiers with Reference

Detailed Description

The MAX4069–MAX4072 bidirectional, high-side, cur-

rent-sense amplifiers are ideal for portable equipment.

The wide 1.35V to 24V input common-mode voltage

range is independent of the supply voltage, ensuring that

the current-sense feedback remains accurate even when

connected to a battery pack in deep discharge.

The MAX4069/MAX4071/MAX4072 operate from a 2.7V

to 24V single supply. Because the MAX4070 has a

2.5V internal reference, it operates from 3.6V to 24V. All

devices have a low 100µA supply current that reduces to

only 10µA (typ) in shutdown mode. To achieve maximum

flexibility, an external current-sense resistor is used along

with a gain select pin (GSEL) to choose either 50V/V or

100V/V. Drive GSEL low to select gain of 50V/V or drive

GSEL high to choose gain of 100V/V (see Functional

Diagram). The MAX4069 has an adjustable reference

voltage set by two external resistors between REFOUT

and ADJ, and GND pins. The MAX4070 contains an

internal 2.5V reference. The MAX4071 is similar to the

MAX4070 but with a fixed internal reference voltage of

1.5V. The MAX4072 has a reference input pin to allow use

of external references. Charging current is represented

by an output voltage from the reference voltage to VCC,

while discharge current is given from the reference volt-

age to GND. The direction of VSENSE is totally arbitrary.

The input stage of the MAX4069–MAX4072 is shown in

Figure 1. Its unique topology allows for monitoring bidi-

rectional currents through the sense resistor (RSENSE).

If, for instance, current flows from RS+ to RS-, the

MAX4069–MAX4072 match for the voltage drop over the

external sense resistor(RSENSE) by increasing the cur-

rent through the internal Q1 and RG1. At the same time,

the current through Q2 and RG2 decreases, however,

internal circuitry not shown in Figure 1 prevents Q2 from

turning off completely. Likewise, if current flows from RS-

to RS+, the current through Q2 and RG2 increases and

the current through Q1 decreases. In this way, the volt-

ages at the input terminals 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 MAX4069–MAX4072, the output signal of amplifier

A2 is level-shifted towards the reference voltage (VREF),

resulting in a voltage at the output pin (OUT) that swings

above the VREF voltage for positive-sense voltages and

below VREF for negative-sense voltages.

Note: RG1 = RG2 = 104k (typ).

RSENSE

RS+

RS-

MAX4069–MAX4072

RG1

RG2

OUT

A1

Q1

Q2

A2

IOUT

Figure 1. Detailed Input Stage

Applications Information

Bidirectional, Current-Sense Amplifier

Systems such as laptop computers and other devices that

have internal charge circuitry require a precise bidirec-

tional, current-sense amplifier to accurately monitor the

battery’s current regardless of polarity. Figure 2 shows

the MAX4069–MAX4072 used as a bidirectional current

monitor. In Figure 2, the direction of VSENSE is assigned

to charge and discharge, assuming charge is greater than

discharge. The practical choice of direction is based on

dynamic range at OUT, given that the range of REF to VCC

is usually greater than from REF to ground. This is useful

for implementing either smart battery packs or fuel gauges.

High-Current Measurement

The MAX4069–MAX4072 can achieve high-current mea-

surements by using low-value sense resistors, which can

be paralleled to further increase the current-sense limit.

Adjusting VREF (MAX4069)

The MAX4069 has an output reference voltage that

can be set to a desired voltage by a two-resistor divider

between REFOUT, ADJ, and GND. If REFOUT and ADJ

are connected together, the minimum output reference

voltage is obtained, 1.23V (typ). The maximum voltage

for REFOUT is 4V (that requires VCC ≥ 5.1V). The rec-

ommended range for the external resistors is: R1 + R2

should be > 20kΩ and < 500kΩ.

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