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Input offset current in OPA188 and OPA192

Denis Molaro
Prodigy 80 points
Other Parts Discussed in Thread: OPA192, OPA188

Dears, 

for a new product that I'm developing I need a very stable operational amplifier with a very low thermal coefficient. So I'm comparing the OPA188 with the OPA192.

The OPA188 have very good performance in input voltage offset drift -> Max is 0.085 uV/°C

The OPA192 is not so good -> Max is 1 uV/°C

If I look these parameters, for my application, I should use the OPA188, but if I look the Input offset current I see that:

The OPA188 have a maximum input offset current of 6 nA

the OPA192 have maximum input offset current of 2 nA

I'm not sure how the input offset current is changing over the temperature and so I'can not be sure any more that OPA188 is the best chose for me because if the offset current is changing up to 6nA over the temperature I can have output voltage drifts even higher than use the OPA192.

Why the data-sheets are not stating any data about input offset current drift over temperature?

Thanks for any help.

Denis

  • 0
    TI__Guru 68651 points

    Denis,

    All IB data you request for OPA188 and OPA192 is in the datasheet.  The maximum input offset current is +/-2800pA at 25C and it is maximum of +/-6nA at 125C.  We also show a typical graph of IB vs temperature in Fig 10 - see below.

    OPA188 IB vs Temp

    Likewise, the maximum OPA192 Ios is 20pA at 25C and it increases to max of 2nA at 125C; also, please see Fig 19 below showing the typical graph of IB vs Temp.

    Notice that Ios in OPA188 is twice as great as either IB because in chopper amplifiers the input bias current goes into one input BUT comes out of the other input terminal.  This is not the case in all other type of op amp like OPA192 - Ios is always smaller than either of IB's.

  • 0 in reply to Marek Lis
    Prodigy 80 points

    Marek,

    thank you for the nice explanation.

    Since the OPA188 is a chopper amplifier and the two input bias currents are in the opposite direction, I can not use the compensating resistor to null the output offset due to input current offset:

    Is there an equivalent technique that I can use with chopper amplifiers to get read of offset bias current?

    BR

    Denis