LM48511 Feed-Forward Compensation

Matthew Depew11

Other Parts Discussed in Thread: LM48511

I have a question about value selection for RFB3 according to the datasheet section on Feed-Forward Compensation for the LM48511.

My design is very similar to the reference design. R3=25.5K, C1 = 270pF (Nobody had 280pF in stock)

I have a 100uF tantalum on the output with an ESR of 1 ohm. According to my calculations that should put the value of RFB3 at 370K. The reference design has a 2.5K resistor for RFB3. Why am I getting a value two orders of magnitude larger than the reference design? According to my calculations, for 2.5K to be the correct compensation, the ESR of the tantalum on the output would need to be 7.5mOhms, which is not something you can buy in a tantalum cap.

over 7 years ago

0 José Luis over 7 years ago

TI__Mastermind 20085 points

Hello Matthew

Welcome to E2E, thanks for your interest in our products.
I have reviewed your calculation and that is right. Regarding ESR of the tantalum capacitor, I was searching and I found that tantalum-polymer capacitors have ESR values approximate to 7.5mΩ.
Please let me know if you have more questions or comments.

Best Regards
Jose Luis Figueroa
Audio Applications Engineer | LPAA

0 Matthew Depew11 over 7 years ago in reply to José Luis

Prodigy 30 points

Can you send me an example of a 100uF tantalum cap with an ESR of 7.5mOhm? I'm seeing numbers more like 100mOhms.

0 José Luis over 7 years ago in reply to Matthew Depew11

TI__Mastermind 20085 points

Matthew,

You could have a look to the following parts T520V107M006ATE007 and T520V107M006ATE009. I hope that this helps you.

Best Regards
Jose Luis Figueroa
Audio Applications Engineer | A-Team

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LM48511 Feed-Forward Compensation