LMR23625: feedforward capacitor

Tomoaki Yoshida91

Genius 5255 points

Part Number: LMR23625

Hi team,

Our customer is designing circuits using LMR23625.

They are concerned about the need for feedforward capacitors and constant design.

How can we decide whether this is necessary?

They want to reduce the number of parts, so I do not want to implement Cff unless necessary.

If necessary they will decide Cff according to the following formula in the data sheet.

Rfbt is 12kohms and Cout is 44uF.

Cff is calculated as 175pF.

I tried to check with webench, but I can not check the Bode plot because the capacity value is not recommended and I can not input it.

Could you check whether this constant is okay?

Best regards,

Tomoaki Yoshida

over 6 years ago

0 Orlando Murray over 6 years ago

TI__Mastermind 22299 points

Hello Yoshida,
Do you have a load step specification?

The feedforward capacitor Cff helps with the transient response of the switcher.
You can also use an electrolytic capacitor with higher ESR to eliminate the need for Cff at the cost of increased output ripple.

Even though WEBENCH does not update the loop response, the pspice transient models are available to simulate the LMR23625.
If you have a schematic we can further assist you.

Regards,
-Orlando

0 Tomoaki Yoshida91 over 6 years ago in reply to Orlando Murray

Genius 5255 points

Hi Orland-san,

Thank you for your support.
There is not yet load step specification.

I would like you to check the schematics.
So I would like to send it directly by e-mail.

I will apply for friendship, so please give me e-mail.

Best regards,
Tomoaki Yoshida

0 Orlando Murray over 6 years ago in reply to Tomoaki Yoshida91

TI__Mastermind 22299 points

Yoshida,
Sorry for the delay!

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LMR23625: feedforward capacitor