TPS54561: PWM switched feedback resistors

Andres Curiel

Part Number: TPS54561

Hi,

I am wondering whether this arrangement to switch the lower side feedback resistor value using a PWM signal and a FET might work OK as a way to dynamically adjust the output voltage on the TPS54561?

Thanks.

over 2 years ago

+1 Frank De Stasi over 2 years ago

TI__Guru 59185 points

Hello

I don't think that would work, since you can not combine the filtering in the feedback.

The large capacitor will add a low frequency pole to the loop.

You will need to filter your PWM first, then apply it as a "DAC" voltage to the FB pin through a resistor.

Then you don't need the FET.

I have attached a spreadsheet that you may find helpful with this type of application.

You will need to test it carefully on an EVM before going into production.

Thanks

DAC_calc4.xlsx

0 Andres Curiel over 2 years ago in reply to Frank De Stasi

Prodigy 20 points

Hi Frank,

I feared that might be the case. Thanks so much for your reply, I couldn't have asked for any more

All the best,

Andres

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TPS54561: PWM switched feedback resistors