AD8605 performances at -55°C

Hi,

I am using this amplifier to create constant current source by driving a MOSFET.

The package is SOT-23.

The amplifier is 5V-supplied.

I know that operationnal range of AD8605 is -40°C/+125°C but I plan to use this op amp at -55°C, and I don't know what behavior to expect at this temperature.

Should I expect only a slight drop of overall performance (in which proportions ?) or should I expect worse ?

I just want to know how much can I be confident in using this component for my application.

Thank you

Regards

  • RP,

      We can only guarantee performance over the conditions stated in the data sheet, but in general,

    unless there is something tricky done with the biasing, op amps are still "operational" outside of

    the stated range.  At hot, the input bias current will all of sudden take off at a certain temperature, etc.

    You can expect changes in ISY, VOS, IBias, gbw, SR for sure.  You will have to look at the part

    at -55 and see if you can live with the changes.  With a limited sample, I would take the deltas

    and multply by three.

    I noticed your company name;  I hope this is for a test bench and not going into space, in which

    all bets are off.

    Harry

  • Harry

    Thank you for this answer.

    I am curious regarding the multiplication by three, is it a rule of thumb or driven by a statistical approach ?

    And what would you consider a "limited" sample ? 3, 5, 10, 100 ?

    Some tests at -55°C are already planned with 18xAD8605 doing the same job.

    By the way, this is not going into space, fortunately.

    In fact the system is heated and will be at -55°C for 15min max, but it has to be available at start-up that's why I want to evaluate the confidence in the circuit behavior during the heating phase.

    Thank you

    Raphael

  • The three X is a rule of thumb.  For example, the max Vos -40 to +125 is 750uV w/ Vss = 5V.

    So I would take 5? parts, preferably at least two date codes (buy them from different distributors)

    and if you read 900uV, make your own number of 2.7mV.   Then calculate if your system will work.

    Yes, on some parts, self heating will get the junction temp from =55 to -40 or -35 or higher within

    a few minutes.  The AD8605 doesn't dissipate much power, so you could add some R directly to

    ground to burn up some more power. (but not too much)

    Harry

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:31 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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