Uni-/Bidirectional Operation

The MAX9918/MAX9919/MAX9920 support both unidi-

rectional and bidirectional operation. The devices operate

in unidirectional mode with VREFIN = VGND. The output

is then referenced to ground and the output voltage VOUT

is proportional to the positive voltage drop (VSENSE) from

RS+ to RS- (Figure 1).

The MAX9918/MAX9919 operate in bidirectional mode

by application of a low-source impedance reference volt-

age in the 0V to VCC - 1.9V range, (typically VCC/2), to

REFIN. For the MAX9920, the reference voltage range

is 0V to VCC - 2.4V (typically VCC/2). The output volt-

age VOUT relative to VREFIN is then proportional to the

±VSENSE voltage drop from RS+ to RS- (Figure 2).

Figure 1. Unidirectional Operation

Figure 2. Bidirectional Operation

IDISCHARGE

RSENSE

LOAD

TO ADC

VCC

GND

RS+

RS-

REFIN

OUT

40mV

10mV

30mV

20mV

0

DISCHARGE

CURRENT

0.9V

3.6V

2.7V

G = 90V/V

5V

1.8V

SHDN

VSENSE

VOUT

MAX9919N

IDISCHARGE

RSENSE

ICHARGE

LOAD

TO ADC

2.5V

VCC

GND

RS+

RS-

REFIN

OUT

-20mV

10mV

20mV

0

DISCHARGE

CURRENT

CHARGE

CURRENT

-1.8V

1.8V

0.9V

G = 90V/V

VSENSE

5V

-0.9V

-10mV

SHDN

VOUT - VREFIN

MAX9919N

www.maximintegrated.com

Maxim Integrated │ 15

MAX9918/MAX9919/MAX9920

-20V to +75V Input Range,

Precision Uni-/Bidirectional,

Current-Sense Amplifiers