[sdiy] LDO regulators and ceramic caps

[Sarah Thompson]

There are a couple of options I have seen. The best is definitely to use an LDO designed for purpose. I have also seen a small value resistor in series with the cap, which would simulate the higher ESR of an electrolytic. 

This kind of thing comes up in my day job because electrolytics aren't good in vacuum (I design spacecraft instruments). Some people do use tants, but I tend to avoid them myself so making ceramics work is my usual option.

Sarah


> On Oct 8, 2015, at 2:34 PM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> Steve Lenham wrote:
> 
>> 1. LDOs exist that are specced for output ESRs down to zero,
>> for exactly this reason - could always simply use one of those!
> 
> Looking at some promising offerings from Linear Technology now.  For some reason I didn't find these "ceramic safe" parts before!
> 
>> It mentions that maximising the distance between the reg and
>> the ceramic caps allows trace inductance to work in your favour.
>> If your PCB is too small for this, perhaps deliberately introducing
>> a _small_ inductance (either discrete or using "wiggly tracks"
>> on the board) might do the trick without impacting on the
>> regulation. Got to be better than resistors - yuk.
> 
> I read that, but I kind of didn't like the thought of adding inductance as my gut feeling said that a low-ESR capacitance combined with an inductor would make a high-Q resonant circuit.  Seemed like that would be asking for trouble, but as you say, maybe it actually acts to stabilise the regulator. PCB is tiny so can't rely on distance to be my friend, and it's full of chips that need ceramic decoupling caps at least every couple of chips, so going to go with one of LTC's "ceramic safe" LDO's, test it for stability and go from there.
> 
> Thanks for your advice,
> 
> -Richie, 
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