[sdiy] LDO regulators and ceramic caps

[Roman Sowa]

You'll have to make real-life test with actual LDO, PCB and capacitor 
anyway, as results may vary.
I use much more capacitance than needed, 4.7-10uF instead of recommended 
0.47-1, and it's stable in whole possible load current range. You can 
also add sub-ohm resistor in series with cap.

There may be huge differences between the same model of LDO made by 
various manufacturers, especially in specs not shown in first page of 
datasheet. For example in dropout stage the ground pin current rised a 
lot (like 10 times) in one mfg part and stayed more or less the same in 
other one.

Roman

W dniu 2015-10-07 o 14:07, Richie Burnett pisze:
> Hi all,
>
> 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.
>
> Just wondering how people are resolving this issue.  My board is quite
> small 2"x2" so it's unlikely that track lengths would add enough
> resistance to the ceramic capacitors to move them into the stable region
> for the LDO regulator.
>
> 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!
>
> -Richie,
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