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UCC256304: Can the X-CAP discharge function of the UCC 256301 or UCC256304 be disabled?

Rick Lai
Prodigy 60 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC256303, UCC256302, , UCC256301

Hi

According to the appnote "SLUA836–UCC25630x Practical Design Guidelines ", the HV pin is not suggested to connect to the DC input .However, in my application, it is possible that the client will use the DC source as the input. So my question is that can this function be disabled by some external circuit? I know there are two other devices(UCC256302 and UCC256303) among this UCC25630x series

which don't incorporate the X-CAP discharge function , however, due to the requirement of without using the PFC stage in my application, it seems that i have to choose the UCC256301or UCC256304 in terms of the need of wide-DC input range.

[My application background]

AC-DC converter:

1.INPUT: 176VAC~264VAC;OUTPUT:35V/3.7A (typ)/9A(peak)

2.Due to the low cost and small dimmension requirement  , the PFC stage can not be added to the converter.

Best regards,

Rick

  • 0
    TI__Mastermind 27145 points

    Hi Rick,

    Thanks for your interest in UCC256304. The X cap discharge function in UCC256301 and UCC256304 cannot be disabled unfortunately. Do you need input over-voltage protection in your application? You could use an external circuit to apply a voltage to the BLK pin of UCC256302 or UCC256303 which would allow you to use either of these devices for your input range.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Prodigy 60 points

    Hi Mr. Lough

    Thanks for for quick reply!

    Actually, I do not need input over-voltage protection in my application, and I need the LLC controller can work with the wide-DC input range.

    As a matter of fact , what i need for my  application from the LLC controller are two things.The first thing is that it can work with the DC source. The other thing  is that it can support the wide-DC input range. The reason that i want to disable the X-CAP discharge function is because when the input of the converter is DC source(eg.250VDC~370VDC), and the HV pin is connected to the DC side then the ucc256301 or ucc256304 will have the risk of running into the overtemperature protection as descriped in the appnote SLUA836. In my application,  we need the converter support  both AC(176VAC to 264VAC ) and DC input ( 250VDC to 370VDC ), but based on the suggestion in the  appnote SLUA836 about the HV pin,I have to make a trade-off.

    Best regards,

    Rick

  • 0 in reply to Rick Lai
    TI__Mastermind 27145 points
    Hi Rick,

    Either UCC256302 or UCC256303 will work in your application. Calculate the BLK divider to start up at 176VAC. You can use a 3.6V zener connected to BLK and gnd to prevent triggering the input overvoltage lockout on these devices. This will allow either UCC256302 or UCC256303 to work with the input range you specified. With UCC256302 you can actually connect the HV pin to your high voltage input through a resistor string if you would prefer having a HV startup function. Let me know if this addresses your questions.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 60 points

    Hi Mr.Lough,

    Thanks for your suggestion.

    You are right, the UCC256302 or UCC256303 will work at the sacrifice of lossing the input OVP function. If i choose the UCC253604, similar situation will happen actually, because in my application, the BLKOVP value will very big with the using of the UCC253604. Your answer have addressed my questions.

    Thanks again.

    Best  Regards,

    Rick