LM62440-Q1: Question on Cff

Justin Phan

Part Number: LM62440-Q1

Hello,

How should I choose the Cff capacitor value?

I plan on using the adjustable output voltage option in my design (LM62440APPQRJRRQ1). The design will have 12V input and 9V output. Max output current is 2.4A. Since the duty factor is VOUT/VIN, then the duty factor is 75%. As a result, I used equation 9 in the datasheet to calculate the minimum inductance for L1 and chose L1 to be 2.2uH:

I wanted to ask how to determine Cff for best transient performance in the given adjustable voltage setup? For now, I set C293 to be 22pF.

Best,

Justin Phan

over 1 year ago

+1 Jimmy Hua over 1 year ago

TI__Mastermind 47060 points

Hi Justin,

I think 33pF should be a good starting point here. The datasheet recommendation in the datasheet Table 10-3 shows 33pF.

I would suggest you take a bode plot loop response measurement before and after the modification to get an idea for the unity gain crossover frequency.

Regards,

Jimmy

0 Justin Phan over 1 year ago in reply to Jimmy Hua

TI__Genius 17280 points

Hello Jimmy,

Thanks for the advice. I will try 33pF for now and modify as needed.

Best,

Justin Phan

Power management

Power management forum

LM62440-Q1: Question on Cff