RS232 transceiver capacitor problem

Thread Starter

gotumal

Joined Mar 24, 2008
99
Dear Reader,

I have used Sipex IC SP3232EET on my board for 3.3V controller. Instead of 0.1uF, I used 1uF tantalum capacitors. I faced a problem of PC not detecting the device sometimes. Then I monitoeed voltage at pin 2 and 6, i.e. +10V and -10V. Some times I get, it but the moment I connect PC serial port, it drops to 1V. I tried using different PC but same observation. Sometimes it gives proper voltage and serial communication works fine. Now when I checked the datasheet, I thought of using 0.1uF capacitor. So I replaced 1uF tantalum capacitors by 0.1uF chip capacitors. But no difference. Did my IC go bad?

Thanks in advance.
 

hgmjr

Joined Jan 28, 2005
9,029
Can you provide a copy of the circuit showing us how you connected the caps to the Sipex part? Maybe we can spot where things are amiss.

hgmjr
 

nanovate

Joined May 7, 2007
666
C109 should be not be connected 3V3 ... it can be connected to GND or to VCC. You have both 3V3 and 5V connected together through 0R0 resistors -- why?
 

Thread Starter

gotumal

Joined Mar 24, 2008
99
Hi,

Actually both the resisots will not be populated at a time. Depeding on the availability of transciever IC which either works on 5V or 3.3V, it will be used. So C109 is connected to Vc only eaither 3.3V or 5V. As of now I am using SP3232 so 3.3V.
 

nanovate

Joined May 7, 2007
666
FYI the output of this chip is +/- 5.5V not +/- 10V.

The connections look OK so maybe you have bad chip or something else is bad.
 

Thread Starter

gotumal

Joined Mar 24, 2008
99
Hi reader,

My problem still persits. Some more data I collected regarding the charge pumps. I had a query of selecting capacitors, their lower and upper limit. I got this information in the document attached.

With this circuit, I am not able to communicate with PC. I am able to see the data which MCU sends before IC but not after IC (towards PC) when I connect the serial cable to PC. The moment, I disconnect that cable, I get the data in RS232 voltage levels. Also to my surprise, if I connect the connector after getting data at other side, my communication works fine. With DSO I found that at pin6 I get 0V if I connect cable, where as I get -5V after disconnecting the cable. Once I get -5V at pin 6, level stays there even after connecting cable. Please help with your suggestions.
 

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Thread Starter

gotumal

Joined Mar 24, 2008
99
Just for your information, I found that those ICs have become faulty. Those were working fine before. So I suspect there could be a problem with a serial port of my PC. I am just checking the voltage levels of all the pins. Will update you if I find any solution.
 
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