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Max232 gets overheated

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abicash

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Hello all

I have used Max232 umpteen times.I know how to connect capacitors.
This time though ,it gets heated and eventually dies.This happens with all 232's

The power supply is 5v steady and stable generated from a 7805 and filtered appropriately.
Pin 2 is connected to 1uf electrolytic capacitor+ve and the -ve goes to Vcc=5v
Pin 6 goes to 1uf electrolytic capacitor-ve and the +ve goes to ground.

Other things are as in datasheet.

I checked TI Max232 and found out a startling thing.It says to connect
Pin 2 connected to 1uf electrolytic capacitor +ve and the -ve goes to GROUND

What could be wrong???

Expecting help as usual :)
 
Hello Mike

Thanks for reading and replying.

Vcc is properly bypassed.

The other pins on the Max are floating ,so is the one connected to the Modem.
Could that be a problem?
 
Hello Mike

Thanks for reading and replying.

Vcc is properly bypassed.

The other pins on the Max are floating ,so is the one connected to the Modem.
Could that be a problem?

hi,
This image shows how to connect the caps.
When you connect from from pin2 to +V, which way around are you connecting the cap.??

As pin2 is at a higher potential than +V
 

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Hello eric thanks for replying

Now there's the problem

Since Maxim datasheet asks to connect the cap +ve from pin2 and the cap -ve to Vcc whereas the schematic you provided asks to connect the -ve to ground :confused:

I have been using the Max for a long time now and always connected from pin2 to +ve and the -ve to Vcc=5v
 
Hello eric thanks for replying

Now there's the problem

Since Maxim datasheet asks to connect the cap +ve from pin2 and the cap -ve to Vcc whereas the schematic you provided asks to connect the -ve to ground :confused:

I have been using the Max for a long time now and always connected from pin2 to +ve and the -ve to Vcc=5v

hi,
It could be a problem with the caps themselves, have you tried a different type/batch of cap.?
I have always connected pin2 as shown in the image,never had problems.
 
Hi

Have tried a lot with different makes and type too (tant ,cer)

I was checking on the web and i found a relevant info when using a modem.
Heres the LINK
The modem in question offered a high pulse after it turns idle and if input pins on the Max are left floating then the voltage tries to enter the max input.
I cant figure out how though since the max has a pulldown at its i/p pin
 
hi,
Read the link.
Does your MAX overheat when not connected to an external device/modem.?

Does the MAX overheat when the external device, when connected, is powered off, carefully touch the MAX and power down the external device, try the same when powering down the PIC/MAX when the external device is connected.
Basically find out when the MAX is overheating.
ie: normal operation, power up/down etc.
 
The Max TTL/CMOS inputs have very weak pullups. In other words, you might want to add some external ones for added stability.
 
Last edited:
Hello

Problem solved.I rewrote the code and it got solved.Max doent heat up at all now.
I think there was some timing issue , couldn't figure out though what was causing it.
 
hi,
when i connect max232 to circuit it offen get heated..........i have left the pins 7,8,9,10,12 floating.....this is the reason y my max get heated????????????
 
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