TPS54541: Changing FB resistors on the fly - while operating

Itay Price77

Part Number: TPS54541
Other Parts Discussed in Thread: TPS25741A, LM5175,

I'm designing a USB3 power delivery circuit, using TPS25741A (USB Power Delivery Host Port Controllers).

inside there is an application example, how to change Vout of the voltage regulator by changing the FB resistors on the fly. the example is using LM5175.

I want to use TPS54541 and change the FB resistors by changing a parallel resisor.

Will it work?

Will I risk myself in a ringing?

Itay

over 6 years ago

0 JohnTucker over 6 years ago

TI__Guru**** 191445 points

In general you can do that. The circuit impact will depend on how much you want to vary the voltage. What are the two voltages you want?

0 Itay Price77 over 6 years ago in reply to JohnTucker

Prodigy 60 points

Hi John,

Thanks for the reply.

I want to switch between 5V, 12V and 20V .

0 JohnTucker over 6 years ago in reply to Itay Price77

TI__Guru**** 191445 points

The difficulty is that TPS54541 is a current mode control device. For current mode control, The lower resistor of the FB resistor divider is part of the AC transfer function. So you will not be able to optimize the compensation for that wide of output voltage range. It will be a compromise that can work for all the voltages. Additionally you may want to consider soft switching to control possible overshoot and undershoot when the voltages are changed.

Typically, we see this type of application for voltage margining where the output voltage is only changed a few percent.

I may have some additional comment later.

Power management

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TPS54541: Changing FB resistors on the fly - while operating