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MSPM0G1507: How to configure op-amp chopping feature

rperezti
Genius 12670 points
Part Number: MSPM0G1507

We are using one of the integrated op-amps configured as an integrator with both inputs and the outputs routed to pins. We need to use the chopping feature but we are not familiar with this and we need some help. Is there any reference material or appnote that explains how to configure the feature per the table below (excerpt from TRM Section 12.2.6)? How do we chose the values in this table and where do we connect the filter components?

  • +1
    TI__Genius 15410 points

    Hi Ruben,

    The filter mentioned in the table you referenced is only required on the output of the op amp if the op amp output is routed externally to a device pin. The RC filter should be set based on the gain setting of the OPA PGA. For example, if you use a gain configuration of 0x2 (Gain = -3x / 4x) you should have an RC filter on the output with a 1kohm resistor and 90nF capacitor.

    If the internal MSPM0 ADC is used to measure the op amp output (routed internally) then you do not need the RC filter on the output of the op amp and should instead use the ADC assisted chop mode in the ADC. 

    Thank you,

    Tim Claycomb

  • 0 in reply to Tim Claycomb
    TI__Genius 12670 points

    Hi Tim, we have a few follow-up questions about this. 

    • We want to route the opamp output to a pin AND route it internally to monitor it with an ADC channel. Is that possible?
    • We use the opamp as integrator. So there is a capacitor between output and in-.  What effect does the gain setting have on the integrator?
    • Do we still need the filter? An integrator is also a kind of filter.
    • Which setting do you suggest for this application?
  • 0 in reply to rperezti
    TI__Genius 15410 points

    1. Yes, they can route the pins externally and then monitor with the ADC channel

    2. The internal PGA should not be used if they are using the op amp as an integrator because the PGA resistors will be in parallel to the components of the integrator circuit. The PGA is intended for only inverting or non-inverting gain. 

    3. If they are using the internal ADC with assisted chop mode, they would not need the external filter.

    4. Do you know what they are using the amp for in the system? Integrators are typically used in control loops but it may be something else.

    Thank you,

    Tim Claycomb