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Opamp Selection - Output leakage current < 1nA, Shutdown, RR

Other Parts Discussed in Thread: OPA357, OPA373, OPA363, OPA341, OPA322

Hi Team!

I am looking for a device that has a max output leakage of <1nA over temperature (0 to 50C) when it is in shutdown. It would need to have a RR swing with VCC at 3.3V and 18k load and have a shutdown output..

Would the OPA357 satisfy this? Alternatively, what are other devices that could satisfy this criteria?

Thanks,

Ben

 

  • Hi Ben,

    From the datasheet plot, that seems reasonnable.  I will move the post to the PA forum as this device was developed by PA.

    Best regard,

    Xavier

  • Ben,

    Shutdown current of OPA357 for Vs=3.3V is around 250nA at 50C (see graph below). 

    Since you only specified RR swing requirement but no speed, I would suggest you to take a look at OPA341 (see graph below) as well as OPA363, OPA373 and OPA322.

  • Hi Marek,

    Thank you for the prompt response! I really appreciate it.

    The spec I am looking for is the leakage current in the output. Is there test data for this? We want this to be <1nA.

    Thanks,

    Ben

  • Hello Benjamin,

    Don't forget the effects of feedback elements that will be in parallel with the output. Do you have feedback? Don't just assume that the only leakages will be the output leakage while it is shut down.

    I am assuming you will be using a "follower", integrator or AC coupled feedback configuration - as any other configuration would have a low impedance path to common.

    A CMOS output stage should have the lowest leakages.

    Careful..Some devices have bipolar inputs, but CMOS outputs for full "R-R" output. The input leakage currents on the inputs may be more than the leakage currents on the output (leaking through the feedback network). Don't assume the input leakages will be less than the output leakages.

    Just to confuse things, some CMOS input devices have bipolar R-R outputs...so it is not guaranteed that a "CMOS" "R-R I/O" device will have a CMOS output.

    Also high voltage (>5V) devices may have anti-parallel protection diodes across the inputs to limit the input differential voltage, and these can create another leakage path between your feedback network and the other input pin..

    Can you give us a hint as to the application so we can make a better suggestion? As Marek asked - Bandwidth? Low iBias input??

    Regards,

  • Ben,

    The shutdown current is a total leakage current so it DOES include the leakage at the output terminal which is typically its largest contributor due to the large size of the output transistors - there is no separate spec for output shutdown current alone.  But as Paul pointed out, the shutdown current does NOT include the current associated with the loading of the output with a resistive feedback network especially in case of bipolar input op amps that typically feature back-to-back protection diodes that could turn-on (even in follower configuration) depending on input common-mode voltage and whether you use pull-up or pull-down output resistor. 

    That said, the op amps I suggested in my previous post are all low-voltage CMOS and as such they do NOT have protection diodes between the input terminals and their typical input bias current is less than 1pA.  If you need further assistance, please provide more details regarding required op amp specifications and/or type of application it is used in.

  • Marek,

    Thank you for that input. I think your explanation has solved much of the confusion that I have had in my explanation to the customer. Unfortunately, I am still looking for more information from the customer and will let you know if I need further assistance.

    Thank you again for your help! I really appreciate it.

    Ben