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Original question:

TPS7A85A: TPS7A85A parallel design

TPS7A85A: Parallel LDO Calculator results

Antonio Girardi
Prodigy 30 points
Part Number: TPS7A85A

Greetings,

first of all, thanks for updating the calculation file for parallel LDOs.

I was trying the latest version but, with the same parameters, i am experiencing large calculation differences compared to the previous version.

See link: previous post on parallel design of TPS7A85 (non-A) LDOs

In particular, the calculated Vₑ high and Vₑ low and the minimum number of recommended LDOs are very different.

Did I miss something?

Thanks in advance

Antonio Giradi

  • +1
    TI__Mastermind 37075 points

    Hi Antonio,

    The latest update to the calculator was only on the "error voltage calculator" tab.  An observant engineer noticed that the tolerances were accidentally divided down by 1000 instead of 100 to obtain the percentage.  In your original design it looks like we assumed 1% resistors so you may want to switch to 0.1% resistors.  Keep in mind that this is a worst case analysis and statistically, you are unlikely to see this worst case solution in production. While the minimum number of LDO's required increased for 1% tolerance resistors, this is from the worst case analysis and statistically this number should be less.  You can always conduct a statistical simulation in PSpice to obtain a more realistic understanding of your tolerances in production, using section 3 of this white paper:

    https://www.ti.com/lit/wp/sbva100/sbva100.pdf

    Thanks,


    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 30 points

    I see, adjusting the tolerances in the error voltage calculator tab solves my problem!

    Thanks Stephen!

    Antonio

  • 0 in reply to Antonio Girardi
    TI__Mastermind 37075 points

    No problem Antonio.

    Let us know if you need anything else.

    Thanks,

    Stephen