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TPS43330A-Q1: How to calculate the power dissipation of bootstrap resistor on TPS43330A-Q1

Part Number: TPS43330A-Q1

Hello Team,

My customer asked how to calculate the power dissipation of bootstrap resistor(Rboot) when adding a Rboot resistor in series with a bootstrap capacitor(Cboot) of TPS43330A-Q1 application circuit. Would you please explain in detail how to calculate this power dissipation of Rboot and send me the relevant apps note if you have?

Best regards,
DY

  • Hello DY,

    we discourage the use of a boot-resistor, since it compomizes the effective charging for the BOOT voltage.

    If the desire is to reduce EMI, here are a few suggests how to improve:

    • Increase component density, reduce trace-lengths, in particular of high dU/dt traces (gate-drive, phase), and minimize loop areas, in particular the FET-Inductor-Rsense-GND-loop.
    • Avoid switching layers on high dU/dt-traces, if unavaoidable, use many, thick vias.
    • Remove (or modify) the snubber. The snubber “cuts” off overshoots, which introduces high frequency content. If overshoots on the Phase-node can be tolerated, it can be removed.
    • To slow down the edges, insert series-resistors into the gate-drive or choose lower-speed FETs. Note: both will increase the switching losses!
    • Potentially, a spread-spectrum-variant, TPS43332, TPS43336 or tPS43351, can be used. With SYNC=high, those parts offer Spread-Spectrum. Note: Spread-Spectrum is prohibited  with SYNC=low or with external Clock!
    • Use Optimized GND-layout (solid GND-planes, but seperate Power-GND (PGNDx) and Signal-GND (AGND). Connect those only underneath the IC.
  • Hi Frank,

    Thanks for your kind reply.
    But my customer keep asking to provide the calculation equation of the power dissipation for TPS43330A-Q1’s Rboot.

    Best regards,
    DY

  • Hello DY,

    I refrain from supporting an implementation that may compromize the behavior of the device.

    Secondly, the boot-recharge depends on external components, particularly the gate-charge of the external HS-FET and associated drainage of the boot voltage during switching.

    Again, please advice the customer to NOT USE a boot-resistor.

    If the customer is concerned about EMI, please suggest above mentioned approaches to mitigate EMI.

    Thanks a lot and best regards,

    Frank