Electrolytic cap as bypass for GSM

[wayneft]

I have a question for you more experienced people out there. I'm making a simple breakout board for a SimCom SIM900D GSM IC and the datasheet recommends a tantalum bypass capacitor of 100uF in parallel with a 0.1 uF ceramic. Instead of using a 100uF I'd actually like to use a cap of at least 1000uF because it looks like it handles the current spikes better with higher values.

The question I have is does anyone see any issues with using an aluminum electrolytic (SMD) cap instead of a tantalum? As you can imagine the price difference between two is extreme. I've done some initial testing with some standard leaded electrolytic caps and didn't notice any issues. What do you all think?

 

[FvM]

You can answer the question yourself by looking at the capacitors datasheet. A low ESR 1000 uF cap with 0.1 ohm ESR or below will be O.K. A standard quality electrolytic cap may have up to 1 ohm ESR. The GSM burst current is 1-1.6 A, depending on the power level, so a standard quality cap will be almost useless.

 

[wayneft]

Thanks for the advice. I think I'm going to stick with tantalum and go with a low ESR (18mOhm) 220uF 10V and see what kind of results I get. Again thank you.

 

[IanP]

In many cases the use of LC combination can provide better solution than just a big capacitor ..
Try something like ..1-100uH.. followed by ..10uF(tantalum)+1-100nF(ceramic) ..

IanP
:wink: