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UCC28180 I-Sense resistor selection

LeonardEllis
Guru 71526 points

On the first prototype power supply, a 20m-ohm I-sense resistor was used and I saw current limit of about 10Arms.  The next pcb design used the same 20m-ohm I-sense, but AC current was limited to 6A.  Changing I-sense to 15m-ohm resulted in 8A limit. 

I'm not understanding why I could get 10Arms in the first design but only 6A now.

  .  

  • 0
    TI__Mastermind 40520 points
    Hello Leonard,

    I will alert the appropriate team to address your question. To save some time, I would suggest for you to investigate and provide any information about other circuit differences between the 2 designs which might bear on the current limit difference between them. The I-sense resistor value alone may not be the sole determiner of the limit. I'm sure the other engineers will ask for the same thing.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Guru 71526 points

    Thanks Ulrich,

      I'm sure you will need to see schematics and pcb layout; what is the best way to get those to the Apps team?

  • 0 in reply to LeonardEllis
    TI__Mastermind 40520 points
    Hi Leonard,

    I expect that when the Apps team contacts you (either through E2E or by internal email), they will indicate the method by which they'd like you to convey the information. I'll ping them again, if you don't get a response sometime today.

    If there are no proprietary restrictions on the schematic and pcb, you can zip up the files (preferably pdf's, not native source files) and attach them to your next post (click on the "use rich formatting" link at the bottom-right corner of the post box, then click the paper-clip icon to attach the zip-file). But if they should not be made public, you'll probably have to send by email. Hopefully, the final resolution can still be posted (maybe in generalized terms), for the benefit of our other E2E users.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Expert 7290 points

    Hi Leonard,

    Can you please tell me the circuit difference of these two design?

    What is your testing condition? There are two over current protection: soft overcurrent protection and cycle-by-cycle current limit. Which one is triggered in your test?

    Thanks,

    Bosheng Sun

  • 0 in reply to Bosheng Sun
    TI__Guru 71526 points
    taken off-E2E direct to customer.