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PMP10478: PMP10478

Xiaobing (Eric)
Intellectual 895 points
Part Number: PMP10478
Other Parts Discussed in Thread: UCC28740, TPS2561A

Hi All,

  Thanks for your time. I have a question in PMP10478 design. When learnt test data, I noted this power could work at constant current mode to charge battery, can I have to know how its work in schematic? Please suggestion and comment. thank you. 

Regards,

Xiaobing (Eric)

  • 0
    TI__Genius 9130 points
    Eric,

    The UCC28740 controller on the primary side has built-in CC-mode overload protection.

    As noted on the schematic for PMP10478, the UCC28740 power stage is designed for >6 A capability.

    From eqn. 3 in the UCC28740 datasheet, Rcs = (Vccr * Nps) * sqrt(eff_TR) / (2 * Iocc)

    Rearranging, Iocc = (Vccr * Nps) * sqrt(eff_TR) / (2 * Rcs) = (0.33 * 20 * sqrt(0.95)) / (2 * 0.51) = 6.3 A

    This is the CC limit for the power stage, i.e. the total current limit feeding both USB outputs.


    On the secondary side, the USB controller TPS2561A will individually limit the current out of each USB port, independent of the 6.3 A primary side limit.

    This is described in the PMP10478 product page on the TI website:
    "The TPS2561A provides accurate and independent current limit protection for each port."

    The individual USB current limit is controlled by the resistor value on the Ilim pin of TPS2561A. 20 k sets Ilim ~1.9 A for each output, or 3.8 A total - this is less than the 6.3 A primary side limit, so that's ok.

    A larger value resistor can be used on Ilim to set higher USB limit, but the max level should be < 6.3/2 = 3.15 A to make sure the primary limit does not occur first.

    I hope this answers your question and resolves your issues?

    Thanks,
    Bernard