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OPA2320: Offset voltage at output with differential input short-circuited

Brian Zoro
Intellectual 2780 points
Part Number: OPA2320

Dear all,

our customer is facing some issues, where I would need some help:

"The problem with the opamp that we have is an offset voltage at the output when the differential input is short-circuited. This means that for example when we have zero voltage or current, we have a remaining voltage to the MCU. We managed to reduce this a lot, and we can compensate for it in the firmware.

This issue decreases our resolution since we cannot use all the bandwidth of 3.3V to represent 1kV, but only 3.3V-0.5V=2.8V. "

Could someone kindly have a look into this?

Many thanks in advance.
Regards,
Brian

  • 0
    TI__Mastermind 47716 points

    Hi Brian,

    Could you post the schematic? If this is inconvenient to present in public forum, please send it via my internal email. 

    Here is Vos of OPA2320 and is RRIO op amp. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Intellectual 2780 points

    Hi Raymond,

    many thanks for quick response.
    Customer is performing additional tests and get some captures clearly showing the issue that they have. 

    Let you know asap.

    Thanks.
    Regards,
    Brian

  • 0
    TI__Guru 60570 points

    Brian,

    The linear output voltage range of OPA2320 is at least 100mV from each rail (see below) so for 3.3V single supply the best you may hope for is to obtain output range from 0.1V to 3.2V;

    As far as the effect of the non-zero Vos on Vout range is concern, this may be calibrated out by first measuring the offset (with zero differential input) and then adjusting the input with opposite to Vos polarity in order to maximize the output range.