[sdiy] Typical ESR of different capacitors

[Antti Huovilainen]

On Wed, 1 Sep 2010, Tim Stinchcombe wrote:

> least one could model it in SPICE). And in fact I was pretty certain 
> that our problem was caused by the ESR being _too low_! In the end we

National Semiconductor appnote 1148 warns against this. AFAIK, inserting a 
ferrite bead after the regulator output cap (electrolytic or tantalum) 
should help isolate the ceramic bypass caps from the regulator.

> memory), we used a brute force approach with another whopping big cap in 
> the reg feedback loop, and really put the zap on its gain.

This was suggested in another appnote, IIRC. Unfortunately I don't 
remember the name or manufacturer of the appnote.

> frequency. I probably still have a list of refs (app notes etc.) on 
> regulator stability, but they're at work, so it will have to wait until 
> tomorrow if you are interested...?

Please send them when you can. Luckily the LP2950 datasheet specifies the 
output cap ESR as 10 milliohms to 6 ohms. L4931, LD1086, LM2937 and LM2940 
limits are listed as 0.1 - 10, 0.5 - 6, 0.03 - 3 and 0.01 - 3 ohms 
respectively. Based on these, I'm guessing that anything between 0.5 
ohms and 2 ohms is safe for most LDO regulators unless otherwise 
specified.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova