ICL7660 charge pump and filtering capacitors

[Rockhorst]

I chanced upon this topic at EEVBlog a while back. Very interesting stuff and fun to see. The thing I took from it and applied to my personal builds is the following. If you use an extra power filtering cap parallel to an electrolytic, a film one is pretty much useless whereas  a MLCC type cap does quite a good job. I've not scoped anything myself but that's what the described experiments suggest to me. MLCC performs at least similar to film at this task and price is also nothing to stop you from using them. Thought that was worthwhile to share.

Edit: Reddesert below points out that I misread scale and that a film cap does seem to have some effect.

[culturejam]

Interesting read. Thanks for sharing.

[reddesert]

I thought the experiments on the first page showed that a 1uf film cap parallel to the electrolytic (Circuit C) reduced the voltage spikes considerably, by about 10x. This may not be obvious, but it looks to me like the scope shots for Circuit C with the film cap are at 5 mV/div while the scope for Circuits A and B are at 50 mV/div.

The later experiment on the second page with the 1uf ceramic cap looked even better in some ways, but the inductive filtering and electro cap were changed also, so it wasn't a direct comparison between ceramic and film. Regardless, it is interesting and when I get some free time, I may try experimenting with added filter caps in charge pump circuits. 

There are some things about the noise most of us have experienced that don't seem (to me) to be totally consistent with the ICL7660 datasheet, which suggests that it ought to be able to run at 10kHz; yet I've gotten whine at lower frequencies, 5-6 kHz.

[Rockhorst]

@CJ: my pleasure

@reddesert: good call on the scale. I've edited the original post to make that clear.