AD8418

Data Sheet

THEORY OF OPERATION

The AD8418 is a single-supply, zero drift, difference amplifier

that uses a unique architecture to accurately amplify small

differential current shunt voltages in the presence of rapidly

changing common-mode voltages.

In typical applications, the AD8418 is used to measure current

by amplifying the voltage across a shunt resistor connected to its

inputs by a gain of 20 V/V (see Figure 26).

The AD8418 is designed to provide excellent common-mode

rejection, even with PWM common-mode inputs that can change

at very fast rates, for example, 1 V/ns. The AD8418 contains

patented technology to eliminate the negative effects of such

fast changing external common-mode variations.

The AD8418 features an input offset drift of less than 500 nV/°C.

This performance is achieved through a novel zero drift

architecture that does not compromise bandwidth, which is

typically rated at 250 kHz.

resistors to the positive input of the main amplifier, which allows

the output offset to be adjusted anywhere in the output operating

range. The gain is 1 V/V from the reference pins to the output

when the reference pins are used in parallel. When the pins are

used to divide the supply, the gain is 0.5 V/V.

The AD8418 offers breakthrough performance without

compromising any of the robust application needs typical of

solenoid or motor control. The ability to reject PWM input

common-mode voltages and the zero drift architecture

providing low offset and offset drift allows the AD8418 to

deliver total accuracy for these demanding applications.

+

G = 20

OUT

0V

EMI

FILTER

EMI

FILTER

0V

70V

AD8418

+IN

–IN

–

GND

–50A

50A

Figure 26. Typical Application

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