• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 49 subscribers
  • Views 539 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA314: Input Bias Current diagram not very useful in linear scale

Stefan Langer
Prodigy 125 points
Part Number: OPA314
Other Parts Discussed in Thread: OPA336, LMP7721

Hello TI,

would it be possible to get the datasheet of OPA314 updated (or the underlying data)
such that the input bias and offset current plots (figure 14) have a logarithmic current axis?

The linear axis does not provide useful information in the -25...75°C region!

Log scale should be the standard for this plot, other opamps prove that, e.g. OPA336 done right.

Thanks!

  • 0
    TI__Guru 60610 points

    Stefan,

    We currently work on refreshing our datasheets but it will take some time before they all can be complete.  In the meantime, please find below OPA314 Input Bias Current vs Temperature graph shown on the logarithmic scale.  One thing to know about the reverse-biased leakage current, like the one dominating most of the CMOS and JFET op amps IB, is that this type of current roughly doubles every ten degrees C.

  • 0 in reply to Marek Lis
    Prodigy 125 points

    Thank you very much, Marek - very helpful!

    It is said often these currents double every then degrees, but there are (and will be more) exceptions.

    For example look at MAX9914: also an CMOS amplifier but I_bias really is different from OPA314.

    I'm continously working on the lowest edge of currents with full industrial range in mind - so this is a lasting topic.

  • 0 in reply to Marek Lis
    Prodigy 125 points
    Hello Marek, how about the input offset current? It was in the same diagram....
  • 0 in reply to Marek Lis
    Prodigy 125 points

    And, by the way, is there data available (I_bias, I_offset) vs. Temperature for LMP7721?

    There is only rough data in the table.

    This would come handy for a new design I'm working on.

    Very sad that this OPAMP is not available in smaller packages such as SOT23 or SC70.!

  • 0 in reply to Stefan Langer
    TI__Guru 60610 points

    Stefan,

    OPA314 input offset current, Ios, has the same magnitude as IB (+/-1pA) so it will follow the same curve as IB even though their polarity may be different.

    The only exception to this rule of input bias current doubling every ten degrees C is if the IB is NOT dominated by the reverse-biased leakage current as is the case with chopper, auto-zero or bipolar input transistor amplifiers.  

    MAX9914 IB vs Temperature graph makes no sense with the IB largest at cold temperature - I suspect they allow vapor condensation to affect their measurement.

    I have created graph of IB and Ios vs Temperature for LMP7721 based on datasheet table specifications - see below.