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Original question:

OPA211-HT: Op Amp application in very high temperature (250 C)

OPA211-HT: Op Amp application in very high temperature (250 C)

nader niakan
Prodigy 30 points
Part Number: OPA211-HT

Tool/software:

Hi,

This is related to my previous thread on OPA211-HT

I have the following questions:

1. Since Ios at 210 C is 150 nA(max) and I am using this op amp at 210C, with gain of about 700, should I be concerned about the effect of Ios on my output ?

2. I know Vos drift is 2uV/C, but what is the drift of Ios -- are the drifts linear up to 210C ? 

Thank you

  • 0
    TI__Mastermind 22347 points

    Nader, 

    1. Ib will translate into and offset voltage when it passes through the source impedance and feedback network impedance of an op amp.  Ios is the mismatch of the Ib on the inverting and non-inverting inputs.  If Ios << Ib you can balance the impedances to cancel the effects of Ib (i.e. Ibp x Rin = Ibn x (Rf || Rg) ).  In this example, Ios is not really very small compared to Ib so canceling will not help.  Thus, you should really just pay attention to the offset introduce by Ib x Rin and Ib x (Rf || Rg).  Below is the calculation method for converting Ib to Vos (taken from analog engineers pocket reference ).
    2. Figure 14 illustrates the Ib vs temperature up to 125C.  Since the specification at 125C is 200nA and at 210C it is 250nA this is a good sign that the curve will remain relatively linear across temperature.  As a rough approximation you could assume Ib = 0nA at 0C and 250nA at 210C.  This would give a drift of 1.2nA/C.  This specificaion is not tested, but this is a reasonable worst case approximation for Ib drift.

    I hope this helps.  Best regards, Art

  • +1 in reply to Art Kay
    Prodigy 30 points

    Thank you, Art. Things are clear now. Thanks. I will close this thread. But, before that, could you suggest a triple or quad op amp with high temperature capabilities ? Thanks