I'm thinking of building something like this:
Now, the MAX232 needs 1.0 uF tantalum capacitors.
Mouser stocks a dizzying array of Ta capacitors. Any suggestions on which ones would suffice? (I'm looking for the cheapest ones that will do the job.)
Now, does the MAX232 need 1.0 uF capacitors? Or will 1 uF be good enough?
Thanks,
Michael
LOL ! Go for some aluminium caps.
Graham
Hi, Michael. The MAX232 uses the 1uF tantalum caps as a charge pump voltage doubler/inverter to change the +5V into a +/-10V for the RS-232. Tantalum is used because it has low ESR at the charge pump frequency (above 10KHz AFAIK). Any solid tantalum cap will do, cheaper is OK. You didn't specify whether you wanted radial or axial through hole leads, or whether you wanted SMT caps, so you don't get a definitive answer, but you can look yourself.
I took an opportunity to look at the Mouser selecttion using their product selector, and found that most of the items listed are non-stock, or require a large minimum order. If you want a cheapie onesies part, and you can live with a radial through-hole part, their P/N 80-T350A105M25AT (1uF 25V molded radial lead, Kemet) goes for $0.31 ea. in single quantity. It will work, and you could do worse.
Make sure to watch the polarities of the caps -- they *will* explode in quite startling fashion if you install them bass-ackwards.
Good luck Chris
Ok, thanks for the information.
Is tantalum actually required? I later looked at a TI MAX232 spec sheet (again from Mouser), and there's a Note 2 there: Nonpolarized ceramic capacitors are acceptable... (page 7)
Is it ok to take this advice, or am I better off just getting the tantalum...? (reduced noise, etc.?)
Thanks,
Michael
The charge pump droop is proportional to the ESR of the caps. I've used many of the x232 parts (now second sourced by TI) and ceramics work great without the problems of tants.
1uF ceramics rated at 2x the expected peak voltage should be just fine.Cheers
PeteS
You may want to consider replacing the MAX232 with one of its newer cousins.
The MAX202 and MAX 2323 are pin compatible and need much smaller caps.
The MAX203 and MAX233 need no caps at all, but are not pin compatible.
-- RoRo
Thanks, I'll definitely look into the MAX202 (99c, DIP, in stock @Mouser).
Michael
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.