Xiaofan Chen wrote: > On Fri, Apr 17, 2009 at 7:56 AM, Bob Blick wrote: >> I'm going with Vitaliy here. The 1uF requirement is for bulk >> capacitance, not low ESR. Any cap will work perfectly fine. >> The resistance in the switching elements is higher than the >> ESR of the worst electrolytic. > > Sorry I do not quite understand you. What do you refer > by "switching elements" here? The on resistance of the charge pump transistors. It defines the peak current. > The discussion topic here is the power supply "bypass" > or "decoupling" caps and I agree with Olin that in general > electrolytic is not recommended in this application. It > might work in some cases. Why shouldn't it work in any case? It's a low speed device and needs bulk capacitance. > The Maxim datasheet shows a polarized capacitor. > I would assume that they mean tantalum capacitor > or similar. Actually I would think a ceramic capacitor > is more suitable nowadays. Why assume it's a tantalum capacitor? Why not assume it's an electrolytic? I realize that we're talking about Maxim, but if you look at the TI datasheet for the MAX232, it says on page 7, "Nonpolarized ceramic caps are acceptable. If polarized tantalum or electrolytic capacitors are used, they should be connected as shown" with the diagram showing polarity marks on the appropriate ends. So as far as TI is concerned, any of the three types of capacitor is OK with them. And I say the choice of 1uF is for bulk capacitance, and that their allowance of any type of capacitor backs that statement up. Cheerful regards, Bob -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist