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UCC256404: Determining the ratio of BMTl BMTh

Keith Keller
Expert 7260 points
Part Number: UCC256404

Hello,

We are working with the UCC256404 and trying to calculate burst mode values.

From the datasheet, we came up with the values for Rll/ss1 as 390k and Rll/ss2 as 180k. We are using Option 6 to determine the ratio of BMTl:BMTh by selecting proper BW  pin resistors.

Based on those 2 resistors, we are getting burst threshold voltage of Vbmt_h = 0.491V and Vbmt_l = 0.295V.

Our question is what Rll/ss3 resistor should we select to make sure the converter only goes to burst mode when PFC_ON is disabled. Is there any calculation we can use to do that ?

Thank you, Keith

  • 0
    TI__Genius 16155 points

    Hi Keith,

    You want to run the LLC converter in the burst mode when PFC is off. Is my understanding correct?

    Could you send me the resonant inductor current RMS values (at both Vmin and Vmax) when PFC is disabled and PFC is enabled for your design? 

    I should be able to answer your question once you send me these values.

    Regards

    Manikanta P