What could cause the output of an LD1117 Voltage Regulator to increase above its specification?

[SCamp.1041]

My design is using an LD1117S33CTR voltage regulator. I am experience some rather odd behaviour where the regulators output is actually increasing from the expected 3.3V all the way up to 4V.

What could cause such behaviour? I am stumped.

[MasterT]

Oscillation comes to mind. Have you properly bypassed IC with caps at the input / output? Check out data sheet of the product for manufacturers recommendation regarding capacitor sizing, ESR, etc.

[SCamp.1041]

So if you take a look at the schematic below, I think this is a pretty standard design no? The LD117 gets supplied by a 5v switching reg. Could a capacitor cause oscillation?

 

Regarding the oscillation, is there a way to use a scope probe to detect this?

[MasterT]

It's a good idea to use a scope, especially if it has SA mode. I read

https://www.st.com/resource/en/datasheet/ld1117.pdf

unfortunately ST doesn't specify type of the capacitor at the output just says 10uF . But based on my experience with LDO, most of them work better with aluminium caps due to intrinsic 0.1-0.5 Ohm ESR. You may try different caps or if ceramic caps in use, than set a small 0.1 resistor in series with cap.

[SCamp.1041]

Ok, I will have to give this a read and test this out tomorrow. So oscillation can increase the voltage?

[Piranha]

https://community.st.com/s/question/0D53W00001aJmYvSAK/output-capacitor-type-for-use-with-ld1117