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'[PIC:] MAX232 Capacitors???'
2004\04\29@202835 by Colin Constant

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Is there any reason not to use the 202?  It also uses 0.1, I think.


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2004\04\30@012036 by Andre Thomas

I have at various times (on designing) used any variation from 100nF up
to 10uF on the 3232 and 232 parts from both Maxim and Sipex. In any
event, usually we would use 100nF in production because of its physical
characteristics and I have never had problems with these.

The capacitors are just for the inverter circuit to generate the dual
rail supply for the rs232 side of things. Since the sink rate on a rs232
is incredibly low increasing the values of the capacitor (thus
increasing the sink rate of the 232/3232 circuit) has little effect in
terms of improved operation.

Perhaps *and I mean really big perhaps* a circuit with 100nF would fail
on a rs232 port that's 10 or so years old where a 1uF or 10uF would have
worked better (due to the fact that the current consumption of the older
serial port **might** be higher). Changing capacitor values may also
have other effects, but as for opperational effects I have not witnessed
any for values from 100nF to 10uF -

-----Original Message-----
From: pic microcontroller discussion list
[PICLISTspamKILLspamMITVMA.MIT.EDU] On Behalf Of Colin Constant
Sent: Friday, April 30, 2004 2:25 AM
Subject: Re: [PIC:] MAX232 Capacitors???

Is there any reason not to use the 202?  It also uses 0.1, I think.


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2004\04\30@071528 by David VanHorn

Why not follow the chip specs, and use at least that size cap/type of cap?

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2004\04\30@081657 by Spehro Pefhany

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At 06:15 AM 4/30/2004 -0500, you wrote:
>Why not follow the chip specs, and use at least that size cap/type of cap?

;-)  Now there's a novel suggestion.

Note that the capacitors effectively end up like a resistance (in series
with other resistance that you can't affect) in series with the output
drivers. Larger capacitance => less resistance => more drive available.

Using low values of capacitance may mean you can drive more cable length
at a faster baud rate. But the first step is to RTFM, as David says.

Big capacitors are not very expensive these days (1uF ceramics or 10uF
electrolytics) so there's no reason not to go a little higher than the
minimum if it helps. Note that Z5U and similar class II dielectrics
lose most of their capacitance at low temperatures so if you have a wide
temperature range to deal with, you may either have to use a much higher
capacitance or to spec a better dielectric (X7R is a good compromise
in many cases).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"             Info for manufacturers:
Embedded software/hardware/analog  Info for designers:

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2004\04\30@111146 by Matt Redmond

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Thanks guys.  As I pointed out in my original post, I did 'RTFM' and what it said was inconsistent with every example circuit I've ever seen.

I was simply pointing out the inconsistency and asking which approach was correct.

>>Why not follow the chip specs, and use at least that size cap/type of cap?<<

>>;-)  Now there's a novel suggestion.<<

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