Low-Cost, Precision, High-Side

Current-Sense Amplifier

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5

5

µs/div

START-UP DELAY

GND

500mV/div

V+

2V/div

GND

MAX4172-10

10

µs/div

V+ to PG POWER-UP DELAY

GND

PG

2V/div

V+

2V/div

GND

100k

Ω PULL-UP RESISTOR FROM PG TO +4V

MAX4172-11

______________________________________________________________Pin Description

____________________________Typical Operating Characteristics (continued)

resistor from OUT to ground will result in a voltage equal to 10V/V of sense voltage.

OUT

6

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 MAX4172

V+

8

Ground

GND

5

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

FUNCTION

NAME

_______________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

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

ing the input bias current), so A1’s negative input is

gain forces its positive input to essentially the same

voltage level as the negative input. Therefore, the drop