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OPA2141: Unexpected behavior when replacing OPA2197 with OPA2141

Gabriel Calin1
Prodigy 30 points
Part Number: OPA2141
Other Parts Discussed in Thread: OPA2197, , OPA197, OPA2140

Hello everyone,

We noticed an unexpected behavior when using OPA2141 as a replacement for a OPA2197 in a simple follower stage of a circuit. I did a simple simulation using TI-TINA and noticed the same behavior:

Using the OPA2197 as a follower, 5V single supply, with a sine source (2.5V DC level, +/-2.4V amplitude, 5Hz), the output is as expected, with the output reaching close to the rails (0.1V~4.8V):

Just replacing the ampop with a OPA2141 model results in a very different behavior

The output only goes from 0.15V to about 1.5V.

I noticed if I increase the supply to 8V or above, it starts working close to expected.

Based on the datasheets both models should work rail-to-rail from a 4.5V single supply.

Shouldn't the OPA2141 in this simple follower configuration, low freq signal, work exactly the same as the OPA2197 when using a single +5V supply rail?

Gabriel

  • 0
    Prodigy 30 points

    I just noticed the input common-mode voltage of the OPA2141 is (V-)-0.1 to (V+)-3.5V. The OPA2197 has a VCM of (V-)-0.1 to (V+)+0.1.

    Is this severe VCM restriction of the OPA2141 due its JFET design?

    Gabriel

  • +1 in reply to Gabriel Calin1
    TI__Guru 57641 points

    Hi Gabriel,

    Gabriel Calin1 said:
    Is this severe VCM restriction of the OPA2141 due its JFET design?

    Yes, OPA197 is considered Rail to Rail Input/Output (RRIO) op amp. Its output is clipped a bit due to the 1kΩ load per the 5V single supply. 

    OPA2140 is not Rail-to-Rail Input op amp, but it is RRO by design. That is why you observed the behavior, since it the input is not operating in a linear region due to the input Vcm. 

    Here is an example of OPA2140 simulation in linear operation.  

    OPA141 Single Supply 10072022.TSC

    If you have additional questions, please let us know. 

    Best,

    Raymond