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MAX471ESA

Precision, High-Side Current-Sense Amplifiers

Maxim Integrated 

Precision, High-Side

Current-Sense Amplifiers

RS+

RS-

RS+

RS-

MAX471 SIGN

OUT

GND

3V

TO

36V

RS+

RS-

RS+

RS-

MAX471 SIGN

LOGIC

SUPPLY

100k TO LOAD/

CHARGER

OUT

GND

VOUT

1k

POWER

SOURCE

OR

BATTERY

3V

TO

RG1

36V

RSENSE

TO LOAD/CHARGER

RG2

LOGIC

SUPPLY

100k

1 SHDN MAX472 OUT 8

2 N.C.

3 RG1

VCC 7

RG2 6

ROUT

4 GND

SIGN 5

Figure 3. Paralleling MAX471s to Sense Higher Load Current

Figure 4. MAX472 Standard Application Circuit

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 18µA. 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).

8 _______________________________________________________________________________________

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