AD8418A Relationship between VREF pin setting and offset

Hi team,

I am designing with AD8481A for bidirectional current detection.

VREF1 and VREF2 are used in parallel as shown in the block diagram below, but a buffer circuit is used to shift VREF from 1 / 2Vs.

An RC filter is inserted to remove the noise in this buffer.

From the experiment, I noticed that the output common mode voltage deviates from the design value.

https://ez.analog.com/amplifiers/differential-amplifiers/f/q-a/164319/ad8418a-r1-r4-values/371545#371545

It was found that the VREF1 and VREF2 terminal voltages were slightly shifted from the design because the resistor was inserted externally.

Also, since I found the internal resistance value from the following thread, I would like to estimate the offset due to inserting the resistance externally.

At this time, I would like to consider how much the offset varies, but should I assume that the internal resistance will vary at worst?

I found from the data sheet that the relative precision was about ± 0.5%, but I didn't know the absolute precision.

I think that the gain will be affected by adding a resistor, but could you please tell me the formula for calculating the effect on the gain?

Best regards,

T-yoshi