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-

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 100k

Ω 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

mance.

Resistor Selection

Since OUT delivers a current, an external voltage gain-

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

- 1.5V (see the

Current Output section).

Precision, High-Side

Current-Sense Amplifiers

8

_______________________________________________________________________________________

MAX471

RS+

RS+

RS-

RS-

SIGN

OUT

GND

TO LOAD/

CHARGER

3V

TO

36V

MAX471

RS+

RS+

RS-

RS-

SIGN

OUT

GND

1k

100k

LOGIC

SUPPLY

3V

TO

36V

1

2

3

4

8

7

6

5

MAX472

RG2

100k

RG1

POWER

SOURCE

OR

BATTERY

TO LOAD/CHARGER

RG1

N.C.

SHDN

SIGN

OUT

GND

RG2

LOGIC

SUPPLY

Figure 3. Paralleling MAX471s to Sense Higher Load Current

Figure 4. MAX472 Standard Application Circuit