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TPS54060: Bootstrap cap value

Rohit J
Intellectual 850 points

Part Number: TPS54060

Hello,

The datasheet recommends a 0.1uF value for the bootstrap cap. In my current implementation, SW node is pre-biased because my output has a battery and my Vin - Voutis not very high (~ 3V). At lighter loads, I see a n operation where it appears that the part is switching for a while, then shuts-down for a short duration. This behaviour is periodic. It can be reduced and. consequently, eliminated by increasing load current or by increasing Vin - Vout.

That leads me to believe this is a ' bootstrap cap not having enough charge ' issue. Do you agree?

As an experiment, I reduced the value to 0.02uF and noticed a significant improvement. Do you foresee any adverse effects in operation over time by reducing it to this value?

Thanks,

  • 0
    TI__Genius 11085 points
    With smaller boot cap, I agree it is charged faster. It discharges faster as well, the boot voltage will have a steeper slope downward when the internal switch is on. As long as the boot voltage is ok in your application at each corner (min/max Vin, min/max temperature, min/max load), it should be fine.

    What is the (Vin-Vout)/Vout when you observe the boot cap issue? For this part, I typically do not recommend duty cycle >90%. It is more likely to happen at lighter load.