Dear All,
Please don’t take this mail as a beginner mail. I have really a serious problem that turns my twelve months product design to a waste.
I designed a an RS232 interface board and used MAX232CWE+ 16 wide SOIC
I used 1uF/50V SMD Case B Aluminum Electrolytic capacitors for MAX232. I use a generic 100nF SMD capacitor as a decoupler of MAX232.
You can see my sch. and layout parts below;
Here is my problem,
When I connected my system to a PC serial port via an RS232 cable (19200 baud and no parity, etc);
1. There is no problem first. System is communicating correctly.
2. I started to disconnect and connect the serial port periodically while my finger was on the MAX232 to measure the heating J
3. In some way MAX232 is starting to overheat and the serial line is starting to not working.
4. If I close my system while MAX232 is heating, waits MAX232 get cold for nearly 1 minute and plug the system again there is no problem. MAX232 is working well.
5. If I don’t close the system, MAX232 is damaged because of the heating.
6. I dumped the problem with an oscilloscope. When I send some bytes to the system via a PC I should see nearly 12,13V if there is no problem but when the IC is damaged, I see only 1V at the R1IN pin (13. Pin) of MAX232. So I’m sure that MAX232 R1IN pin was collapsed the PC transmit signal. Please note that none of five capacitors for MAX232 was not damaged or heating up.
7. I changed the MAX232 IC and all of the rouitine is starting again. I did this nearly 10 times J
8. Please also note that I double checked the capacitors polarity. There is no problem for all
9. In maxim site It tells about an ERRATA for MAX232CWE+( Product Change Notice 801-ERRATA) ; However I couldn’t find this document. I suspected that this IC has a BUG that I encountered
10. I’ve searched the internet for 1 week and there are same problems but all of explanations are about look at the directions of the caps, etc.
11. I found a forum thread on TI forums below and a person named David connected a 20 ohm series to MAX232 VCC and solved his problem. It is not a good but may be a reasonable solution
http://e2e.ti.com/support/interface/etc_interface/f/392/t/123614.aspx
12. I know there is a TI employee could check my problem in detail. If you do I’ll be very glad
Waiting for your urgent reply
Ertan