AMC1200 Gain Query

Carlos de Leon44

Other Parts Discussed in Thread: AMC1200

Hi Pete,

We have designed a new circuit with the AMC1200. The schematic and the test circuit are attached.

With two independent power supply, and a potentiometer between VINN-VINP when the input voltage is 150mV the output is 380.

Why is the gain different to 8?

Thanks in advance.

Carlos.

over 8 years ago

0 Carlos de Leon44 over 8 years ago

Prodigy 80 points

0 Pete%20Semig over 8 years ago in reply to Carlos de Leon44

TI__Mastermind 25825 points

Hello Carlos,

I have moved this thread into the Precision Data Converters Forum for further assistance. I support instrumentation amplifiers, so I'm not much help when it comes to the AMC1200.

0 Tom Hendrick over 8 years ago in reply to Carlos de Leon44

TI__Guru**** 180761 points

Hi Carlos,

In your 'hand drawn' schematic, you have VIN(-) referenced back to GND1, but I don't see that same connection in the board or the CAD drawing above. I suspect you might be violating the common mode input of the AMC1200. Tie pins 3 and 4 together either directly at the chip or on the J3.1 side of R2 and see if that resolves the issue.

0 Carlos de Leon44 over 8 years ago in reply to Tom Hendrick

Prodigy 80 points

Dear Tom,

That was the problem.

Thanks.

Carlos.

Elefante Embebido.

0 Carlos de Leon44 over 8 years ago in reply to Tom Hendrick

Prodigy 80 points

Dear Tom,

This schematic represent our application. The voltage in the shunt resistor is lower than 250mV. However we need to protect the AMC1200 against accidentally over voltage. What do you recommend to limit the input voltage up to 250mV?

Thanks

Lisandro

Elefante Embebido

0 Tom Hendrick over 8 years ago in reply to Carlos de Leon44

TI__Guru**** 180761 points

Hi Carlos,

The measuring range of the AMC1200 is only +/-250 mV, but the input can actually go the the AVdd1 rail without damaging the chip. You can add some low leakage schottkey diodes from the inputs to the rails.

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AMC1200 Gain Query