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OPA2277: Does the OPA2191 have the same feature as OPA2277 automatic offset current cancelation?

Marvin Cantos
Expert 6895 points
Part Number: OPA2277
Other Parts Discussed in Thread: OPA2191

Hi Experts, 

Good day! Please help with the inquiry of the customer below.

"We currently have the OPA2277 in a number of designs with the -Ve input at ground rather than through a resistor due to the automatic offset current cancelation circuit.
Does the OPA2191 have the same feature?
OPA2277 states The input stage base current of the OPAx277 series is internally compensated with an equal and opposite cancellation circuit.
The resulting input bias current is the difference between the input stage base current and the cancellation current.
This residual input bias current can be positive or negative.
Is it true of the 2191" 
Appreciate your help.
Thank you.
Kind regards, 
Marvin
  • 0
    TI__Guru* 93105 points

    Hello Marvin,

    The OPA2191 is a CMOS op amp and does not employ input bias current cancellation. Although sometimes employed with FET input op amps it is most commonly applied to bipolar input op amps such as the OPA2277 that have inherently higher input bias currents.

    The OPA2191 input bias current is stated as ±5 pA typical, ±20 pA maximum (TA = +25°C). The input current is primarily the leakage current of the input ESD protection diodes. The polarity depends on which of the two protection diodes dominates.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Expert 6895 points

    Hi Thomas, 

    Thank you for your prompt response. Appreciate your help.

    Can you help suggest an alternative for OPA2277 that may fit the customer's application considering his designs with the -Ve input at the ground rather than through a resistor due to the automatic offset current cancelation circuit.

    Thank you.

    Kind regards, 

    Marvin

  • 0 in reply to Marvin Cantos
    TI__Guru* 93105 points

    Hi Marvin,

    Please provide a schematic of the current circuit so that I can see the customer's exact OPA2277 use.

    Regards, Thomas

    Precision Applications Engineering

  • 0 in reply to Marvin Cantos
    TI__Guru 68541 points

    Marvin,

    Adding to Thomas' comments, OPA2191 IB current is 1000 times lower than the cancelled IB of OPA2277 and thus it does not need IB cancellation. Also, unlike OPA2277 with Vcm specified 2V from either rail, OPA2191 input common-mode voltage is rail-to-rail and thus will work well in a single supply application you seem to refer to.