Switches & multiplexers

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LMR51430: Where does the Cff CAP comes from?

Robert-Cristian Togan

Prodigy 20 points

Part Number: LMR51430

Tool/software:

So I used the power design tool for the LMR51430XFDDCR (all the details are in the screenshot). In the design I have a Cff CAP that doesn't appear anywhere in the datasheet of the component. I am curious why is the cap there and also where should I place it when I am doing the layout of the switch(see screenshot 2). Thank you for your time!

+1 Frank De Stasi 1 month ago

TI__Guru 64285 points

Hello

The CFF capacitor is used to help improve the loop response of the regulator.

It is connected directly across the resistor RFBT as shown in the Webench schematic.

Since some designs do not require a CFF, it is not shown in the typical PCB layout example.

CFF should be placed close to RFBT. CFF, RFBT and RFBB should all be close to the FB pin

of the regulator.

Thanks

0 Robert-Cristian Togan 1 month ago in reply to Frank De Stasi

Prodigy 20 points

Should the CFF CAP be between RFBT and RFBB or it doesn't matter as long as it is close to the FB pin?

0 Frank De Stasi 1 month ago in reply to Robert-Cristian Togan

TI__Guru 64285 points

Hello

As long as they are all somewhat close, it is OK.

Thanks

0 Robert-Cristian Togan 1 month ago in reply to Frank De Stasi

Prodigy 20 points

Thank you for the help!