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OPA277: offset trim range

Kazuto Tatsumi
Intellectual 2820 points

Part Number: OPA277

Hi team,

My customer needs information about the offset trim range of OPA277UA. How much is the range?

This is because he has concern the case the default offset value is too large and it cannot be trimmed by 20kR potentiometer.

Regards,
Kazuto

  • 0
    Guru 140200 points

    Hi Kazuto,

    this should not present a problem when you take a high quality multi-turn cermet trimmer.

    But, of course, you could replace the 20k trimmer by a series circuit of "5k1 fix" + "10k trimmer" + "5k1 fix", or similar.

    Kai

  • 0
    TI__Guru* 93105 points

    Tatsumi-san,

    The OPA277 offset voltage trim range is designed to exceed the op amp's offset voltage specifications. See datasheet Figure 24, "OPA277 Offset Voltage Trim Circuit." If the customer is attempting to null a system's total offset, then it may not have sufficient range to do that. See datasheet Section, "7.3.2 Offset Voltage Adjustment."

    Any OPA277 that is not capable of having its offset fully nulled as Section 7.3.2 describes should be considered suspect.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0
    TI__Guru 71421 points

    Adding to Thomas' comment, use offset voltage adjustment technique ONLY to null the offset of the operational amplifier. Using the adjustment to compensate for offsets voltage created elsewhere in a system will result in the increase of the offset voltage drift by ~3.3uV/C per 1mV of offset adjustment.

  • 0 in reply to Marek Lis
    TI__Intellectual 2820 points

    Hi Thomas, Marek,

    Thanks for your comment. I understood that it is not possible to compensate the total system offset by trimmer, but the range with 20kR potentiometer is enough to make the OPA277 individual offset null, so that the customer doesn't need to concern about the range. Is my understanding correct?

    Regards,
    Kazuto

  • 0 in reply to Kazuto Tatsumi
    TI__Guru 71421 points

    Hi Kazuto,

    Yes, this is correct - the Vos trim range using 20k potentiometer exceeds the OPA277 maximum offset voltage specification (see below).