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OPA838: OPA836 vs OPA838 for Ultrasonic Gas Meter

Michael Jeong1
Expert 2610 points
Part Number: OPA838
Other Parts Discussed in Thread: OPA836, EVM430-FR6043, TIDM-02003,

Hello Expert,

We changed from OPA836 to OPA838 according on EVM430-FR6043 to what is specified in the TIDM-02003 reference design.

When we changed OPA838 from OPA836, the performance was slightly better in general environment.

However, if there are influences such as surrounding noise or vibration, the performance of OPA838 seems to be more affected than OPA836.

Do you know or explain what's the reason?

Also, could you please guide for circuit to improve at influences such as surrounding noise or vibration w/ OPA838?

Best Regards,

Michael

  • 0
    TI__Genius 11000 points

    Hi Michael,

    Would it be possible to show what result you are seeing when comparing the OPA838 and OPA836? As for the circuit, is everything in the circuit kept the same as the original reference design when swapping the two devices and was there anything that was changed when switching the amplifiers? This is something the team would need to look into to try to find an explanation. One quick debug step could be to maybe try increasing the feedback capacitor to say 100pF from the 33pF. The OPA838 might be a little more unstable than the OPA836, which increasing the feedback capacitor should help. This is just a quick check to see if there are any major changes in the OPA838 performance. 

    Best Regards,

    Ignacio 

  • 0 in reply to Ignacio Vazquez Lam1
    Expert 2610 points

    Hi Ignacio,

    Thanks for your feedback.

    We hope you understand that we are currently unable to share our customer's test results due to insufficient preparation.

    First of all, we would like to confirm the following contents that is mentioned in TIDM-02003 reference design.

    "The OPA838 can provide enhanced standard deviation performance up to 2.5x lower than the OPA836 and is a drop-in replacement."

    If you have comparative data on why OPA838 is better than OPA836 and the biggest difference in specifications, please share.

    Based on this comparable data, our customer would like to select a product.

    Best Regards,

    Michael

  • 0 in reply to Michael Jeong1
    TI__Genius 11000 points

    Hi Michael,

    The excerpt highlighted in the design document referencing the performance upgrade is based on the OPA838's higher gain-bandwidth product and lower input voltage noise compared to the OPA836. A table that highlights the performance difference between the two devices can be found here. The 2.5x performance upgrade is referring to the spec differences.

    Best Regards,

    Ignacio