TPS54308: Can this regulator be used in a quasi passthru mode

jerry wasinger

Part Number: TPS54308

I have an application that uses this buck regulator to generate 5VDC. I -could- have an occasional situation where the input voltage would drop to 5VDC. Since the datasheet claims that this device can have a 100% duty cycle, I was wondering if that implies a pass thru mode and I could get away with a 5VDC input.

Thanks!

Jerry Wasinger

Pi-Plates.com

over 7 years ago

0 Sam(MPAA) Zhang over 7 years ago

TI__Mastermind 19080 points

Hi Jerry,

According to the datasheet, it can have a 100% duty cycle as long as the BOOT to SW pin voltage is greater than 2.1 V typically.

The voltage between BOOT and SW pin is used to drive the high side MOSFET. When the part is operating at 100% duty cycle, voltage between BOOT and SW drops. When it hits the BOOT UVLO(Typ 2.1V), the part will turn on low side MOSFET to charge the boot cap and consequently Vout start to drop, until the voltage is over BOOT UVLO threshold again. This process will lead to large ripple on the output.

If there is any further question, please let me know! Thanks!

Best Regards,
Sam Zhang

0 jerry wasinger over 7 years ago in reply to Sam(MPAA) Zhang

Prodigy 30 points

Thanks! I have a follow up question. If I pull ENABLE low, could I directly drive the SWITCH pin with another 5VDC supply?

0 Sam(MPAA) Zhang over 7 years ago in reply to jerry wasinger

TI__Mastermind 19080 points

Hi Jerry,

Do you mean by driving the output of TPS54308 with another 5VDC supply when VIN is close to 5VDC?
If so, you can do like that as long as ENABLE is pulled low.

Best Regards,
Sam Zhang

0 jerry wasinger over 7 years ago in reply to Sam(MPAA) Zhang

Prodigy 30 points

Sam, one last question: can I drive the output of the TPS54308 with another 5VDC supply if ENABLE is LOW and VIN is floating?

0 Sam(MPAA) Zhang over 7 years ago in reply to jerry wasinger

TI__Mastermind 19080 points

Hi Jerry,

I think you can do like that. I don't have TPS54308 EVM at hand, but I valid it on another part's EVM.
Enable is pulled low, a voltage is applied on VOUT, there will be a voltage on the VIN due to the high side MOSFET body diode. The part is disabled and no swithing happens.

Best Regards,
Sam Zhang

Power management

Power management forum

TPS54308: Can this regulator be used in a quasi passthru mode