• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 473 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC2897A: T(on) and T(off) Variations

Ryan.Bishop
Expert 3900 points
Part Number: UCC2897A

Hello,

Over temperature, do Ton and Toff vary proportionally, or do they vary asymmetrically over temperature.  I can understand (and expect) the switching period varies over temperature.  What I’d like to better understand is how Ton and Toff relative to each other can vary, which can affect the actual maximum duty cycle.

Thank you,

Ryan B.

  • 0
    TI__Expert 3095 points
    Hi Ryan B.
    Both Ton and Toff are set by externally generated currents that are mirrored onto an internal timing capacitor. For this reason I would expect them to track each other as temperature changes.
    It would be unwise to design a circuit that relies on this behavior since it is not published in the datasheet.
    The maximum duty cycle is published in the datasheet across the full temperature range. This is the figure that you should use for your designs.
    Thanks
    Joe Leisten
  • 0 in reply to Joe Leisten
    TI__Expert 3900 points

    Hi Joe,

    Okay great, thanks for the reply.

    Excuse my ignorance here, but I have a follow up question. The maximum duty cycle is spec'd at 66%/70%/74% under the test conditions Ron=Roff=75k, Rdel=10k. 

    Section 8.3.1.3 of the datasheet seems to suggest the duty cycle will be a factor of Ron and Roff.

    So will the maximum duty cycle always be +/-4% of what is set in datasheet equation (5) across temperature?

    Regards,
    Ryan B.

  • 0 in reply to Ryan.Bishop
    TI__Expert 3095 points
    Hi Ryan B.
    Values presented in the datasheet will have been tested in production and are guaranteed.
    Unfortunately it is not possible to extrapolate the same duty cycle accuracy for resistor values that are significantly different from the conditions given. It should give an indication of accuracy for different resistor values but this is not guaranteed.
    Thanks
    Joe Leisten