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UCC28700-Q1: how to understand the VVDD(on) and VVDD(off) parameters in UVLO function

Jay wang
Intellectual 1931 points
Part Number: UCC28700-Q1
Other Parts Discussed in Thread: UCC28700

hi experts

i saw VVDD(on)  and VVDD(off) parameters in UCC28700 datasheet. it seem like these parameters are related with UVLO function.

so how to understand these two parameters?

does VDD turn-on threshold means that when UCC28700 is start-up, VDD voltage should be higher than 21.0V, otherwise IC cannot start-up?

does VDD turn-off threshold means that when UCC28700 turn off, VDD voltage should be lower than 8.1V, otherwise IC cannot turn off?

  • 0
    TI__Mastermind 22405 points

    Hi Jay,

    Thank you for the query on UCC28700.

    The Vdd pin has a abs max of 38V.

    So at start up, until the output voltage is high enough and aux winding voltage is high enough to take over, the Vdd voltage will ramp upto 21V. If there are no faults, the voltage on vdd will be set by Nas*Vout (which will be vary depending on the loading of the converter).

    If there is any fault, the Vdd cap will reduce voltage, and it will reach turn off point of 8V where it will again start the next ramp up to 21V. During normal operation, Vdd will be operational down to 8V below which it will enter auto restart mode.

    Regards,

    Harish