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Original question:

UCC24650: Putting flyback output diode on high side when using UCC24650?

UCC24650: How to choose wake up resistor value?

James Zhan
Expert 4365 points
Part Number: UCC24650
Other Parts Discussed in Thread: UCC28730,

Hi team,

My customer is using UCC24650 with UCC28730 to build a zero-power flyback converter. Could you please help on the below items from the customer as below?

  • How to choose the value of resistor on WAKE PIN
  • Hot to get the dIsec+/dt value?
  • How to get the Lstray value?

If you need any more infromation, please let me know.

James

  • 0
    TI__Mastermind 26645 points

    Hi James,

    Thanks for your interest in UCC24650. The stray inductance and dIsec/dt are dependent on the diode rectifier package and the pcb layout. The Lsum*dIsec/dt term is accounting for the additional voltage drop caused by the parasitic inductance.

    A wake resistor is only needed if there is considerable stray inductance causing the maximum source-current rating to be exceeded and we have a number of reference designs which have no wake resistor at all. I would recommend estimating the parasitic inductance and dIsec/dt based on the flyback design, rectifier package and estimated PCB trace length to pick an initial value for Rwake. The wake resistor can then be optimized based on bench test.

    Best Regards,
    Ben Lough