input bias current of AD8638

Hello,

during evaluation of AD8638 I experienced a higher than expected biascurrent.

The device was (accidently) out of regulation with:

  - inverting input at 0V

  - noninverting input at -2V

  - Powersupply was +-6.7V

In this situation there was a current of approx 10uA flowing into the noninverting input (and appearingly out of the inverting input)

I reproduced the behaviour twice. The pcb board is reasonably clean.

Possibly this large input current is related to some kind of autozero switching. Can someone elaborate on this or point to reference material on this subject? Under which conditions is the datasheet specification of the bias current valid? How should it be measured?

Best Regards

Norman Werner


  • 0
    •  Analog Employees 
    on Sep 21, 2015 11:00 PM

    Hi Norman,

    You can read through the article at this link for more information on auto-zero amplifiers. There is some reference to the effect that the auto-zero architecture has on the bias current of the amplifier. The article at this link, on the other hand, provides some information regarding bias current and how it can be measured.

    The bias current of the AD8638 at a supply of 16V has a maximum specification of 75pA at ambient. 10uA seems too large a value for the bias current. How did you measure this value? Would you be comfortable sharing your schematic? What is your application?

    Thanks,

    Kris

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:11 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.

    Thank you,
    EZ Admin