[sdiy] LDO regulators and ceramic caps

[Richie Burnett]

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,