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MAX232E: Capacitor

Yuta Nishie
Genius 5015 points
Part Number: MAX232E

Hi,

My customer is planning to implement TMK107BJ105KA-T in C1, C2, C3 and C4 of the following circuit diagram.

Datasheet: https://html.alldatasheet.com/html-pdf/641924/TAIYO-YUDEN/TMK107BJ105KA-T/1474/2/TMK107BJ105KA-T.html

Can I use this capacitor?

Are there any problems such as DC bias characteristics and delay?

Best Regards,

Nishie

  • +1
    Guru 317280 points

    The datasheet says that "ceramic capacitors are acceptable".

    The DC bias characteristics of small ceramic capacitors are bad, but the tolerances of electrolytical capacitors also would be bad.

  • +1
    TI__Guru 52382 points

    Hi Nishie,

    They should be fine to use - that being said it would be better if you could get the next voltage rating up (25V) to avoid the derating of the capacitors. Ceramic capacitors effective capacitance starts decreasing quite significantly below the voltage rating. In general we try to suggest - if using ceramics (which in most RS-232 device designs ceramic is the most common) - that the voltage rating be 2x the maximum voltage that would be seen. Since this devices charge pump is outputting +/-8.5V typically that would be 17V - which would generally mean the best capacitor would be 25V rated.  The current capacitors used has an appx.  -30% derating under 8.5V DC (which the output of charge pump is mostly DC) which is pretty significant. 

    Most likely it won't cause too much issue, if any, but the derating of the capacitors is a bit high and I'd recommend 25V rated ceramic capacitors (if you can find 17V or 18V caps that would work - but I think 25V would be the next most common variant that is widely available) 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson