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PMP9087: Design calculation on R4, R5 value

Takeshi Sasaki
Expert 4480 points

Part Number: PMP9087
Other Parts Discussed in Thread: UCC28710

Hi team,

Could you give me comment on following customer question?

Q1. How can I calculate R4 and R5 value on PMP9087 for following current requirement? 

For the customer's design, average current: 300mA, peak current: 2A. 

Best regards,

Takeshi Sasaki

  • 0
    TI__Expert 6670 points

    Hi Sasaki-san, 

    I have asked the original design Sean to help on your question, please allow him some time to respond.

    Thanks,

    Robert 

  • 0
    TI__Expert 4840 points

    Sasaki san,

    Current sense resistor (R5) is determined by the following equation: Rcs = Vccr/(2*Iocc), where Vccr = 0.33 (from datasheet) and Iocc as output over current level.

    Assume Iocc=2.1A, we will have to use Rcs = 0.079ohm.

    For line compensation resistor (R4), just use equation (27) in UCC28710 datasheet for calculation. Turns ratio Npa = 1. 

    Use 124ohm for R4 should be good.

    Also, in my calculation, to handle 2A peak, the inductor should have inductance <60uH.

    Regards,

    Sheng-Yang Yu