Re: Wanna see what happens when you don't read the data ***?

On Feb 28, 4:28 pm, Hawker
<Hawker{removethispa...@xxxxxxxxxxxxxxxxxxxxxx> wrote:
On 2/28/2007 12:01 PM, The digits of JohnPopelish'shands composed the
following:

The low ESR capacitor plus resistor guarantees a stable RC zero over the
life and operating conditions of the system. Getting the zero from some
poorly controlled and unstable resistance from a high ESR capacitor is a
ticking time bomb.

Gotcha. Do you have any data to show trends of ESR change over time and
temp. In the case of the regulator in question it can use a fairly wide
range so if you hit in in the middle I wonder if it is overkill to
assume it could fall outside that range.
(snip)

It varies a lot from manufacturer to another, and from one product
line to another. But you can rely that almost any change from new and
room temperature ambient will increase the ESR. With most LDO
regulators the problem is that all but the lowest cost capacitors are
too low in ESR, so either you pick an unstable cheap one, or a little
more costly, more stable one and add a 2 cent resistor to make it
work, now and over the long term. If the load includes lots of little
bypass capacitors in parallel to the one at the regulator output,
having a lot more than the absolute minimum resistance in series with
the main filter capacitor may be essential for initial stability.
Then you don't have much margin for having the ESR of the capacitor go
up as that capacitor ages or gets cold.

I have given up on hitting a good zero in the response just by
selecting a capacitor for LDO regulators. Fro the price of a
resistor, I sleep better and get less aggravated.

.