LM2842 - controller stability with very low ESR output capacitor

Ewan Coldicott

Other Parts Discussed in Thread: LM2842

Hi all,

I am currently selecting components for an LM2842X-based buck regulator. The regulator will have a maximum input voltage of 35V, output voltage of 5V, max load current of 0.5A and min load current of 25mA. While looking for a suitable output capacitor, I've noticed that ceramic capacitors of capacitance 50-100uF have very low ESR. For example, the TDK C3225X5R0J107M has an ESR of just 3.5mOhm at 550kHz (from its datasheet: http://www.tdk.de/templ/campaign30/DATA/C3225X5R0J107M(Data%20Sheet).pdf). The LM2842 datasheet states that the output capacitor should have an ESR of 0.1 Ohm or less, but does not specify a minimum requirement for controller stability.

My question is, is there a minimum output capacitor ESR required for stability when using the LM2842?

Regards,

Ewan Coldicott

Final year Computer Engineering student, University of Canterbury

over 13 years ago

0 Denislav Petkov over 13 years ago

TI__Mastermind 19891 points

Hello Ewan,

I don't think there is a minimum ESR requirement for LM2842. The restriction is on the other end - when you have high ESR. Low ESR ceramic caps should be fine.

Page 10 of the datasheet has a recommended design for 5V output. You can also use WEBENCH design tools to check the loop response.

Regards,

Denislav

0 Ewan Coldicott over 13 years ago in reply to Denislav Petkov

Prodigy 20 points

Hi Denislav,

Thanks for the response. I went ahead and used a capacitor with an ESR of ~2mOhm @ 550kHz and have had no problems with controller stability during testing of the prototype.

Cheers,

Ewan Coldicott

Power management

Power management forum

LM2842 - controller stability with very low ESR output capacitor