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OPA227: offset voltage is slightly different between before and after temperature cycling

K.Yaita
Guru 29690 points
Part Number: OPA227

Hi Team,

My customer is evaluating offset voltage of OPA227 under thermostat bath.
He said offset voltage is slightly different (~0.5uV) between before and after ambient temperature cycling. (20°C -> 90°C -> 20°C)
Is it possible case for OPA227?

I also suspect it may application issue (thermal mass, accuracy of thermostat bath, etc..) but would like to know any information if there is.

Best Regards,
Yaita / Japan disty

  • 0
    TI__Guru 60430 points

    Yaita,

    Cycling OPA227 across temperature range causes various materials like die, lead frame, and molding compound to expend at different rate, which changes the physical stress exerted on die inside the package causing shift in the input offset voltage - this is know as thermal hysteresis.   This phenomenon occurs in all IC's and we typically specify its magnitude in the series voltage references but not in op amps.

  • 0 in reply to Marek Lis
    Guru 29690 points

    Hi Marek-san,

    Thank you for your detail explanation.
    I really appreciate for your support.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    Guru 29690 points

    One confirmation, just in case.
    Is the following "expend" typo? Is "extend" correct?
    ----------------------
    Cycling OPA227 across temperature range causes various materials like die, lead frame, and molding compound to expend at different rate,
    ----------------------

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 60430 points

    No, I meant expand but it is similar in meaning to extend.  Under incresed temperature most materials like leadframe and molding compound become larger - see below.

  • 0 in reply to Marek Lis
    Guru 29690 points

    Hi Marek-san,

    I apologize for my misunderstanding..
    I appreciate for your support.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 60430 points
    Yaita-san,

    Each sequence of temperature cycling, especially across the full range from -40C to 125C, reduces significantly the magnitude of thermal hysteresis (perhaps 5x). However, in your particular case where OPA227 shift is just 0.5uV out of +/-200uV maximum spec, you may not see much improvement because you are well within the thermal noise floor of the part: Vnoise_thermal=Vn*√BWn)=3nV/rt-Hz*(8e6*1.57)^0.5=10uVrms, that is 60uVpp.