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UCC256404: help on LLC circuit schematic with using UCC256404, UCC28180, UCC24624

Wenting Wu
Intellectual 2295 points
Part Number: UCC256404
Other Parts Discussed in Thread: UCC28180, , UCC24624, PMP22087

Tool/software:

Hello expert,

Do you mind helping on checking the schematic attached which is using devices, UCC256404, UCC28180 and UCC24624?

Now this is the case, there is no voltage at rvcc for one second after power up. The voltage at blk does not reach the working point voltage approximately 0.8v, pfc does not boost, the voltage of the main circuit electrolytic capacitor is only 310. And then there's another question, for the UCC256404 circuit, I follow the picture on the chip manual to build the circuit successfully output voltage, but there's a click sound in the circuit operation. As the load current increases, the audible frequency also increases quickly and then goes as fast as the switching power is not working. 5482.LLC.pdf新录音+9.m4a

Best regards,

Wenting

  • 0
    TI__Mastermind 40120 points

    Hello Wenting, 

    I support UCC28180 and UCC24624 applications, but I am not well suited to support UCC256404 issues. 

    However, if RVCC is not in spec, then the PFC cannot boost, because VCC for UCC28180 is powered by RVCC.

    If BLK voltage does not rise >1V, then the LLC will not operate, either. 

    I don't know what causes the click sound. 
    However, I noticed in the schematic diagram that both ethe primary and secondary sides have the same GND symbol>
    If the PCB is designed as the schematic is drawn, then there is NO isolation between primary and secondary sides. 

    And if that IS the case, then the AC line voltage may be causing damage to your secondary-side load and/or test equipment if those are not designed to sustain high voltage. 
    Please investigate the Grounding of primary and secondary circuits, and isolate them if that is required. 

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Intellectual 2295 points

    Hello Ulrich,

    Thanks for your feedback. The cusotmer follows reference design, PMP22087 to do solution and here are specifications required, 110/220V50HZ VIN，24V VOUT. 

    Do you mind helping to loop UCC256404 expert as well?

    Much thanks!

    Best regards,

    Wenting.

  • 0 in reply to Wenting Wu
    TI__Mastermind 40120 points

    Hello Wenting, 

    I have looped in someone to support the LLC portion of this thread.  Not sure when he will respond. 

    What is the maximum power level of the 24V, please? 

    PMP22087 has a different ground (SGND) for the LLC secondary output than the ground for the primary side (primary ground is not explicitly named). 
    You customer's schematic shows the same GND symbol for both primary and secondary sides, without any explicit distinction.  Usually this indicates that they are all on the same GND reference and there is no isolation to the output.  
    As I mentioned earlier, please investigate this and correct it if it is true.

    Regards,
    Ulrich 

  • 0 in reply to Wenting Wu
    TI__Intellectual 1000 points

    Hi, I work on UCC256404. Can you please provide me the design calculator for LLC section so that I can understand the problem? For sound, can you please confirm the sound is coming at only burst mode or out of the burst mode or throughout the operation?

    Also, what Uli mentioned, please give two different grounds for primary ground(PGND) and secondary ground(SGND).

    Regards,

    Sougata