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UCC256302: UCC256302 question

Masazumi Ishii
Genius 3945 points
Part Number: UCC256302

Hello.

I have a question about UCC 25630X.

1
BW terminal (pin 8) is used for external overvoltage protection.
If external overvoltage protection function is not used, is it short circuit with GND?

2
Capacitor connected to LL / SS is a capacitor for soft start, please teach calculation formula of soft start time.

3
Please tell us the recommended capacity of the resonant capacitor on pin 7.

4
What are the conditions to enter burst mode mode?

Thank you.

  • 0
    TI__Mastermind 27135 points
    Hi Masazumi,

    thanks for your interest in UCC256302.

    1. Yes, if overvoltage protection is not desired, please ground the BW pin.

    2. soft start time will depend on the SS capacitance and also the capacitance in the Vcr capacitor divider in addition to your power stage components such as how much output capacitance you have, etc. I don't have an algabraic expression I can share for the soft start time but the relationship is smaller capacitance in the Vcr divider results in longer startup time. Larger SS capacitance also lengthens the startup time.

    3. The Vcr capacitance will vary from design to design. I would recommend going through the UCC25630x design calculator to select appropriate values for the Vcr capacitor divider. www.ti.com/.../technicaldocuments

    4. The burst mode threshold is configurable through a resistor divider from RVCC to LL/SS to ground. The controller will enter burst mode when FBreplica is less than BMTreplica. For reference, take a look at section 6.3.3 of the datasheet:www.ti.com/.../ucc256302.pdf

    Best Regards,
    Ben Lough