Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

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15

sive current sensing using milliohm sense resistors to

get high accuracy. Previous methods used the internal

resistance of the inductor in the step-down DC-DC con-

verter to measure the current, but the accuracy was

MAX4209H gain error is 0.25% max at 100x, so the

total accuracy is greatly improved. The 0 to 2V output

of MAX4209H can be sent to an ADC for calculation.

The adjustable gain of MAX4208, can be set to a gain

of 250x using 1k

Ω and 249kΩ resistors, to scale up a

age for wider dynamic range as needed.

ASIC

IN+

IN-

REF

REFIN/MODE

1V AT 10A

ADC

ANTI-ALIASING

FILTER

0.002

Ω

MAX4209H

OUT

+3.3V

Ω = 20mV

OUT = G x 20mV = 100 x 20mV = 2V

IN-

IN+

REFIN/MODE

REF

FB

MAX4208

R4

R3

5V

OUT

REF

R2

FB

R1

G = 1 + R2

R1

BUFFER OUT =

Typical Application Circuit