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UCC2813-2: UCC2813-2

justin peare
Prodigy 30 points
Part Number: UCC2813-2

Hi, I am looking at updating one of our current PSU designs which uses a UCC2813D-2.

I have noticed in the datasheet it states the following regarding the timing resistor.

What is the reason for not using less than 10K and what are the affects of a value less than 10K being used?

  • 0
    TI__Intellectual 2640 points

    Hi Justin! 

    Thanks so much for getting in touch with us! Using the recommended value or greater for the timing resistor maintains a favorable ratio between the internal impedance and the external oscillator set resistor and results in minimal change in frequency over temperature. Using a value of less than the recommended minimum value may result in frequency drift over temperature, part tolerances, or process variations.

    Thanks again for reaching out, I hope this information helps! 

    Aidan Davidson

  • 0 in reply to Aidan Davidson1
    Prodigy 30 points

    Hi Aiden,

    Thanks for the quick reply, I now understand why it should be kept higher than 10K.

    With the existing design it would be useful to know the possible variation in frequency compared to the expected, I understand this will be dependent on actual values used. An indication may provide an idea if there could be problems with the existing design.

    Thanks Justin.

  • 0 in reply to justin peare
    Prodigy 30 points

    Hi Aiden,

    I have found what I am after thanks, the 130R resistance in series with the discharge switch (presumably FET on resistance) is important here too . If the RT value is too low it will not meet the threshold required to switch.

    Thanks

    Justin.