7805 running hot but clock is running fine

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2 years 3 weeks ago - 2 years 3 weeks ago #9284 by Torsten Lang
Hi Ian,
I'm curious - what exact type and brand of the AP1117 do you use? Especially for the AP1117E there is a remark in the datasheet that you must not add small MLCC bypass capacitors directly near the output as the LDO may become unstable. We had this discussion at work a short time ago. Normally you should use a solid tantalum capacitor at the output which have a higher ESR than MLCCs.

Best regards,
Torsten
Last edit: 2 years 3 weeks ago by Torsten Lang.

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2 years 3 weeks ago #9288 by Ian
Hi Torsten, in fact the drawing is not quite up to date, I now use AMS1117-3.3, which seem to be less choosy about the decoupling. They are jelly bean components, so I cannot say the manufacturer.

However, I had not read the stability section of the data sheet in detail, so it's a good point and I just learned something.

Another note on stability is that the input capacitor is a long way away. I'm using the output of the upstream regulator, and that is on the main board. It has always worked, but we're in the real world, and tolerances can always lead you to places you didn't expect to go...

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1 year 11 months ago #9378 by Pjotrke
Hey Ian. After our email exchange I've yet to have received the replacement module. I've sent a follow up mail but I got no reply, so I guess this topic is the way to reach you for a heads up.

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