INA321 gain error

MSP430-Beginner

Other Parts Discussed in Thread: INA321

I'm using INA321 for high side current measurement of MSP430, and I have the following questions:

1) In the data sheet, it is not mentioned, which is the minimal differential shunt voltage that can be measured by INA321. Does this change with common mode voltage?

2) I set the shunt=100 Ohm, and I sweeped the current from 0A ... 100uA. I got the following results (attached). In the data sheet it is not mentioned that the gain changes with the load current. How could you explain this? The plot shows that the gain gets stable at the end, but this is not really true, because for ex for 100uA, the gain is 92,22 and for 50uA it is 88,85.

over 13 years ago

0 MSP430-Beginner over 13 years ago

Intellectual 660 points

and here is the circuit

0 MSP430-Beginner over 13 years ago in reply to MSP430-Beginner

Intellectual 660 points

and the gain in function of the load current

Sorry, it was nt possible to upload more then 1 file per answer.

0 Neil Albaugh over 13 years ago in reply to MSP430-Beginner

Genius 5430 points

MSP;

Have you considered the error due to the input offset voltage and common-more rejection? I think it will explain your "problem".

0 MSP430-Beginner over 13 years ago in reply to Neil Albaugh

Intellectual 660 points

Neil Albaugh said:
Have you considered the error due to the input offset voltage and common-more rejection

When I'm sweeping the differential voltage at the input of the INA, the CM voltage is constant, sow why is the output offset not constant as you see in the charts above?

And the input offset in the data sheet is given to be max 1mV. Do you think the input offset gets amplified? Does the input offset change with the diff input voltage? Is there a way to calculate the offset at the output due to CMRR and input offset (I mean formula) so that I can subtract it later from the output result of the INA?

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INA321 gain error