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UCC256404: burst mode soft on off with limited bandwidth SR

Fred Cheng
Expert 5690 points
Part Number: UCC256404

HI  team,

my customer so far decide to use UCC256404 with their current MPS secondary rectifier solution MP6295 which only limited to 300KHz maximum frequency,

what would happen to SR or MOS when burst mode soft on since the frequency would be higher than 300KHz?

which part should we be careful if they insist on this design?

Regards,

Fred

  • 0
    TI__Expert 3431 points

    Hi, Fred:

    Thanks for asking. However, I could not find MP6295 datasheet in website.  There is only MP6925 here. 

    According to the description in datasheet, MP6925 would enter light load mode as pulse width is shorter than 1.6us (typ). So it means SR control would not fire the pulse when frequency approaches 1/(1.6usx2) = 312kHz. SR stops, and current flows to MOSFET's body diode. this threshold can be adjusted by RLL.  

    MP6925 is not TI's product. I can not tell you if there is any potential issue when it applied 300kHz or higher frequency. I suggest you to consults MPS' opinion through your customer. It's the same story. Once SR IC stops working, current flows to MOSFET's body diode and it makes higher conduction loss. MOSFET's might get heat. It also need to consults the MOSFET vendor if this power loss is acceptable. 

    Basically, if this higher frequency happens in burst mode, the power is not high. It has less risk here. However, you still need to ask your customer to consult his vendor to get more clear information. 

    Regards, 

    Wesley