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UCC28950: UCC28950 Rab minimum resistor value check

Ray Chang
Intellectual 1345 points
Part Number: UCC28950

Hi, Team

As the UCC28950's datasheet allowed resistor range on DELAB and DELCD, RAB and RCD is 13 kΩ to 90 kΩ.

If we need to use 12.4kΩ on RAB to get short delay time, does any side effect/concern if we use 12.4kΩ on RAB?

  • 0
    TI__Mastermind 25570 points

    Hello Ray

    There won't be any short term problem in using 12.4k resistor on RAB - and the likelihood of a long term reliability issue is also remote. Having said that, the value in the datasheet has been set so that TI can guarantee the correct operation, especially the  long term reliability of the device under all operating conditions - especially under extremes of temperature. I would suggest that you try to avoid using a resistor less than 13k. If this is not possible then please contact me directly on colingillmor@ti.com because there may be other ways of addressing your specific design issue.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    TI__Intellectual 1345 points

    Hi, Colin

    Due to the efficiency issue, the customer need to use 12.4kohm for RAB delay time.
    If customer must to use 12.4kohm for RAB, what is the risk they need to take?

    How to avoid long term reliability issue if they use 12.4kohm on RAB?


    Could you help to explain more detail about long term reliability issue if they use the 12.4kohm for RAB? Thanks.

  • 0 in reply to Ray Chang
    TI__Mastermind 25570 points
    Hi Ray
    I've replied directly to your email.

    In summary: There is another, better approach they can take.

    Use RAB = 13k to program a baseline delay – probably about 250ns according to Fig 29 in the datasheet. They can then use the adaptive delays to do one of two things
    Adaptively reduce the delays according to one or other of the curves in Fig 29. This involves adding a potential divider at ADEL from CS to GND as shown in the typical application schematic on the first page of the DS.
    Reduce the delay be a fixed amount by adding a potential divider at ADEL from REF to GND – this approach is shown in the EVM schematics. The baseline delay of 250ns set by the 13k resistor can be reduced by a fixed amount set by the potential divider.

    Regards
    Colin