Offset Voltage adjustment for OP177

Dear Sir/Madam,

Our customer asked th following question to me.

As for your OPAMP OP177GSZ,

your datasheet shows the adjustable offset voltage adjustment range is +/-3mV typ by adding 20kohm POT on Rp.

So if we need it +/-6mV, then what is the external Rp value?

10kohm POT?

V+,V-=+/-15V

Maybe this was shown in past sled here but I could not find it sorry

Thanks Kaos

  • Thanks Harry,

    Good advice. I will know the temperature problem to our customer.

    Does Autozero-AMP means current Zero-drift AMP?

    I will recommend your ADA4522-2 to our customer if so.

    Thanks Kaos

  • Kaos,

      You can try a smaller pot, say 10k, but if the customer needs +/-6mV offset adjust, they are

    probably doing a system/signal chain adjust and this is a bad way to do it.  When you do offset

    adjust on a bipolar op amp, you make the TCVos worse.    So at room, you might have a lower

    offset, but at higher temp, it would be worse.  Much better to adjust in some other way.

    For example, if the op amp is used inverting, just add another resistor into the inverting node

    and make it a summing amp.  Or take the offset out in the next stage.  Or why not use an

    autozero op amp?

    Harry

  • Hi Harry,

    Our customer did the following schematic circuit that you instructed.

    But the adjustable offset voltage became narrow range around +/-2.7mV.

    VR5=10kohm

    Can your instructed way apply for the following circuit too?

    Please advice us thanks Kaos

  • Hi Harry,

    Customer have put your OP177 on their inspection device and it have fixed so it cannot replace it to another recommended new device like a ADA4638.

    Therefore customer followed your instructed way adjust the output offset voltage.

    You commented to put the 10k ohm POT on the 1-8 pin, but customer could not bring the expected result.

    So he asked why the adjustment result not so good to us.

    This is the reason why he ask again for OP177.

    As for Instructed way adjustment offset voltage, does it support for V/I converting circuit or not?

    Thanks Kaos

  • Here is additional info.

    Customer is using as X1 buffer amp.

    Thanks Kaos