An electrolytic has a reservoir and smoothing effect which I think is correct, and the ceramic would just filter the ripple. Correct me if I'm off base here With that said, wouldn't the electrolytic be the better choice if you were using just one because it would aid in battery life. I don't think the ceramic has a reservoir capability ... or does it?
Yea, sounds pretty much like the right idea to me. To be specific;
The MLCC caps in have really low ESR, typically around 10m at 100kHz. Electrolytics are typically in the 50 to 100m range.
For the high frequency stuff, ESR is has a more pronounced effect while capacitance value has less effect so a smaller value, lower ESR cap is all you need for that.
For the lower frequency stuff, ESR has less effect and capacitance value has a more pronounced effect so a higher value, higher ESR cap is all you need for that.
By using two ceramics in parallel, you can further improve output quality. For example, two 100uF MLCCs in parallel will produce a cleaner output than a 200uF electrolytic and a 1uF ceramic in parallel. That's because the total ESR for the ceramics in parallel is the 5m range (about half in comparison) which increases performance in filtering the high frequency stuff. The capacitance value is the same so they filter the low frequency stuff just as well if not better with the lower ESR (it still has some detrimental effect even at low frequency).
High value electrolytics are still considerably cheaper than high value MLCC caps so that's a consideration. If performance and compact size is of most importance, then high value MLCCs in parallel are going to be the best option. If low cost is of most importance, a high value electrolytic and low value ceramic in parallel is the best option.
