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TPS65279: About the Vin UVLO and Vbootuv question

Anders Yang
Prodigy 570 points
Part Number: TPS65279

Hello, two questions below:

1. 100% duty cycle means this device support Vout=Vin=5V if we neglect the very small voltage dropout?

2. About UVLO, there is a Vin UVLO and another Vbootuv. Whichf one will be first triggered?

If a design with 5V and 3.3V output. When Vin decrease from 12V, when will UVLO be triggered?

  • 0
    TI__Genius 15135 points

    Hi, Anders

    1. "100% duty cycle" means high-side MOSFET try to keep turning on always, in this condition, the Vout = Vin - drop voltage on high side, when loading is small, you can neglect the drop voltage, when loading is big, the drop voltage will increase, if Vout is below its target voltage, IC will trigger OCP.  So under 100% duty cycle condition, IC cannot output big loading.

    Actually, it is just close to 100% duty cycle, it cannot reach real 100% duty, due to the circuit between BOOT and LX pin consumes current, after a certain time, the (BOOT-LX) voltage will drop below BOOT-LX UVLO threshold, then turn on low-side MOSFET to charge BOOT cap, so the high-side MOSFET cannot keep turning on always.

    2. BOOTUV refers to BOOT cap, Vin UVLO refers to input voltage.

    In your case, Vin UVLO will trigger first.