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UCC256402: higher current draw at low Vin

Keith Keller
Expert 6600 points
Part Number: UCC256402
Other Parts Discussed in Thread: UCC256404, UCC25640EVM-020

Hello,

We are using the UCC256402 in a DC input application (70 - 120V) and seeing higher current draw when we bring the input lower than 95V.

We have been modifying the UCC25640EVM-020.evaluation.  At first we thought the UCC256404 X-cap discharge might be happening, but we're seeing this issue on both the UCC256402 and UCC256404.

Perhaps is has to do with the controller operating above or below resonance?

Thank you, Keith

  • 0
    TI__Genius 13245 points

    Hi Keith,

    In general, LLC resonant converters operate below resonant frequency when the input voltage is lower than nominal voltage (Assuming converter is designed such that it operates at resonant frequency at nominal voltage). So, when you operate at the lower input voltages, for the same power, input current will increase. 

    UCC256404 has a x-cap discharge feature where as UCC256402 doesn't have it. So, in case of UCC256404, You must connect the HV pin to rectified AC voltage whereas in case of UCC256402, it can be connected to either rectified AC voltage or DC input voltage for HV start up.

    Please let me know if you have any further questions.

    Regards

    Manikanta P