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TMS320F28375S: VREFHIx Capacitance

Brian Angiel
Expert 4240 points

Part Number: TMS320F28375S

Tool/software:

Hi team,

I'm updating a design based on F28375S. The existing design used 0805, 2.2uF, X5R caps for the VREFHIx (12-bit mode). Would you recommend adding something like an 0402, 0.01uF, NP0 or something in parallel? Or would it not really have any significant effect on ADC performance?

Brian

  • +1
    TI__Mastermind 36526 points

    Brian,

    We have verified that the ADC will meet data sheet specifications without the need for a small ~ 0.01uF capacitor between VREFHI and VREFLO. On our EVMs for C2000 devices with 16-bit differential ADCs, we use bypass capacitors between 5uF and 25uF between VREFHI and VREFLO. We choose these values based on the recommendation of the voltage regulator.

    It certainly will not hurt to have another small 0.01uF capacitor in parallel, but we do not have any data on whether this will improve performance. My guess would be that there will not be a noticeable performance difference. I think it is more important to have these capacitors as close as possible to the C2000 device pins to reduce resistance and inductance.

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    TI__Expert 4240 points

    Hi Ben,

    I've got another question on this subject. What would happen if we connected a voltage reference device (e.g. REF3500) directly to VREFHIx vs connecting through a buffer? Could we, for example, connect 1x REF3500 to all 4x VREFHIx pins? Do we have any material that addresses this question?

    Brian

  • 0 in reply to Benjamin Collier
    TI__Expert 4240 points

    Hi Ben,

    I did finally stumble upon this post, which seems to address my question. I suppose now the questions are:

    • Do we have any additional details we can share on the performance degradation observed when connecting the reference voltage(s) directly to VREFHIx?
    • Could the specific reference used make a difference? Could a "better" reference voltage device change some of those No's to Yes's?

    Brian Angiel

  • 0 in reply to Brian Angiel
    TI__Mastermind 36526 points

    Brian,

    Brian Angiel said:
    Do we have any additional details we can share on the performance degradation observed when connecting the reference voltage(s) directly to VREFHIx?

    The information in this post was gathered as characterization data, we unfortunately do not have further information to share.

    Brian Angiel said:
    Could the specific reference used make a difference? Could a "better" reference voltage device change some of those No's to Yes's?

    This is totally possible, but I do not think that we will be able to guarantee anything, but instead would recommend that the customer do characterization for their board. If you want to ask about a specific reference part, it may be good to post another thread for the reference team.

    Best Regards,

    Ben Collier