Connect with us

MAX232 capacitors?

Discussion in 'Electronic Basics' started by [email protected], Jan 7, 2007.

Scroll to continue with content
  1. Guest

    I'm thinking of building something like this:

    http://www.circuitcellar.com/library/print/0503/moyer154/2305014-Moyer.pdf

    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
     
  2. Eeyore

    Eeyore Guest

    LOL ! Go for some aluminium caps.

    Graham
     
  3. Chris

    Chris Guest

    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
     
  4. Guest


    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
     
  5. PeteS

    PeteS Guest

    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
     
  6. 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.
     
  7. Guest



    Thanks, I'll definitely look into the MAX202 (99c, DIP, in stock
    @Mouser).

    Michael
     
  8. Wim Lewis

    Wim Lewis Guest

    I've even used electrolytics. Electrolytics presumably have even higher
    ESR at the switching frequency, but, ... it worked.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-