AMC1100: Gain too low

Davide Tasca

Part Number: AMC1100

Tool/software:

Hi everybody,

I use two AMC1100 to measure isolated voltages in our PCB.

I used in the past AMC1100 without problem, but I'm facing some issue regarding the gain of the isolation amplifier. I report the schematic circuit below.

If I measure the input of AMC1100 (pin2-3) differential voltage I get, for example 110mV; and I expect to measure 880mV at the output (pin 5-6) but I measure 809mV (approx 8% error).

I tried to remove R159 and R158 resistors to isolate the amplier output, because I thought it could be a problem of output load, but the situation doesn't change. The power supplies are 4,963V for VDD1 and 4,999V for VDD2.

The fact is that I have two AMC1100 on the board (two analog inputs) and they show the same behaviour.

Does anyone have any suggestion?

thanks and regards

9 months ago

0 Alexander Smith 9 months ago

TI__Guru 55232 points

Hi Davide,

Can you please provide a scope shot showing pin 2-3 and pin 6-7?

0 Davide Tasca 9 months ago in reply to Alexander Smith

Prodigy 10 points

Dear @Alexander Smith,

I think I understood the problem.

It may be related to the input resistors of 2.2Kohm of AMC1100 which probably create a partition with the Rin of the amplifier (see paragraph 7.4 of the datasheet).

I'm going to do a test removing resistors (and output diodes of the LM6482) to see if something changes.

Thanks and regards

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AMC1100: Gain too low