Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdcad!sun!pitstop!sundc!seismo!uunet!tektronix!tekgen!tekigm2!neals
From: neals@tekigm2.MEN.TEK.COM (Neal Sedell)
Newsgroups: sci.electronics
Subject: Re: MAX-232 chip info wanted
Keywords: MAX-232 RS-232 interface data
Message-ID: <4237@tekigm2.MEN.TEK.COM>
Date: 24 Feb 89 06:18:38 GMT
References: <939@calvin.EE.CORNELL.EDU> <464@limbic.UUCP> <1419@ncar.ucar.edu>
Reply-To: neals@tekigm2.MEN.TEK.COM (Neal Sedell)
Distribution: sci
Organization: Tektronix, Inc., Vancouver,  WA.
Lines: 27

In article <1419@ncar.ucar.edu> cook@stout.UCAR.EDU (Forrest Cook) writes:
>In article <464@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes:
>>In article <939@calvin.EE.CORNELL.EDU> phil@calvin.EE.CORNELL.EDU (Phil Erickson) writes:
>>>I've seen numerous references to the MAX-232 chip for TTL/RS232 conversion;
>...
>>The chip supports two RS232 transmitters and two receivers.  This makes
...
>extra +-10V supply if all you need is RS-232.  This may be pushing the specs
>a bit, but we have used the MAX-232 to provide power to a CMOS analog
>mux (DG-509) that is used for selecting on of four RS-232 lines.

Since I have a Maxim spec. sheet here I'll looked it up.  They specifically
allow drawing a "small amout of power" from the V+ and V- supplies.  Typical
output impedence for the V+ supply is ~230 Ohms, the V- impedence is ~175 Ohms.
These are at 5V input and I assume using 4.7uF caps all around since the
adjacent graphs for V+ and V- Supply Voltage vs. Load Current call them out.

Give or take the V+ supply will be 8V with a 10mA load including transmitter
outputcurrent, the V- supply wil be around -7V with a (-)10mA load....
Seems the input is doubled first then inverted, so the actual impedence of
the V- output is Rout+ + Rout- => well over 300 Ohms, the graph is no labeled
consistently on the Y axis.

Happy hacking,

-- 
Neal Sedell