[sdiy] LDO regulators and ceramic caps

[ASSI]

On Wednesday 07 October 2015, 13:07:37, Richie Burnett wrote:
> Out of interest how are you guys and girls dealing with the issue of LDO
> regulator stability with ceramic capacitors?  The datasheets for most
> modern micro's and op-amps preach about the importance of low-ESR 0.1uF
> ceramic decoupling caps across the power pins of the device.  But the LDO
> regulator datasheets say that low-ESR ceramics across the output will
> make the regulator go unstable and are a no no.

Not all LDO and their datasheets are created equal.  Most are designed for 
some finite value of ESR (and often will have a specific type of output cap 
recommended right in the datasheet), but some can go down to zero.  The real 
issue is of course the phase margin of the regulation loop and if you are 
shooting for a specific transient response to load changes you might have to 
look at a far broader range of LDO than simply looking for one that can cope 
with any value of ESR.
 
> I've seen at least one commercial solution that had 100 ohm resistors in
> series with everything fed from the LDO output to isolate the decoupling
> caps from the regulator, but then that series resistance wrecks the
> regulation!

Those 100Ohm seem excessive, so maybe they were trying to do something else.


Regards,
Achim.
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