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UCC256304: X-Cap discharge function

Eddie Koh
Genius 10505 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC256404

Section 7.4.3 of datasheet describes the X-cap discharge functions. 

1. Is there any block diagram in the datasheet that shows this function? 

2. What is the "bleed resistor" value inside X-camp discharge function?

3. Is there any more detailed explanation of how X-cap discharge works, beyond section 7.4.3?

4. Datasheet mentions IEC60065,IEC60950, IEC62368 standards only. Is UCC256304 able to support medical application, IEC60601?

  • 0
    TI__Mastermind 26215 points

    Hi Eddie,

    1. There isn't a publicly available block diagram but what the controller is doing is apply a current sink to ground and looking at the HV pin voltage. If the HV pin voltage is too high, then the controller increases this current sink to try to pull the HV pin voltage low. If the test current sink is unable to pull the HV pin below certain voltage, the controller then determines the AC has been disconnected and applies a much bigger current sink to discharge the X capacitance.

    2. The internal "bleed" is a fixed 11.47mA current source from HV pin to gnd

    3. I don't have further details than this that I can share publicly unfortunately. Please feel free to reach out to me over email if more info is needed.

    4. I believe IEC60601 requires <60V after 1s. Based on the expected maximum delay before the discharge current will kick on, the function will be able to satisfy <60V after 1s for up to 5uF assuming the max AC input voltage is 265Vac. We do not have certification for IEC60601 however.

    I also want to mention we have a newer version of this device called UCC256404 that has a few feature/performance improvements. I would suggest promoting the UCC256404 to your customer.

    Best Regards,

    Ben Lough