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Part Number: MAX232
How are you?
I'm using the MAX232DWR part number in my project to connect in a smart card reader, according attached file.
Sometimes during card reading operation, occurs an overheat in MAX232 IC.
Why is it occuring? Can you help me to resolve this issue?
In reply to Sergio Fink:
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In reply to Hao L:
Correcting the last informations, bellow follows the voltage in no overheat and in overheat states:
1) TI1INI NO OVERHEAT:
2) R1OUT NO OVERHEAT
3) T1IN WITH OVERHEAT
4) R1OUT WITH OVERHEAT
The signals R1OUT (RXD) and TI1INI (TXD) are conected in the IC AP6502SP-13.
1) Is AP6502SP-13 powered up the same time as MAX232? R: Yes, because the supply of AP6502SP-13 is 3.3V from TPS76933. The TPS76933 is supplied from 5V, according schematic bellow.
2) Does MAX232's supply have anything to do with AP6502SP-13?R: No. According last reply, the MAX232 supply is 5V, not 3.3V.
3) After you disconnect R1OUT from AP6502SP-13, do you still see overheat?R: No. The R1OUT voltage when it pin is disconnected is 5V and the overheat does not occur.
Sometimes even with the R1OUT pin disconnected, the R1OUT signal occurs as the picture bellow:
Sergio, One possible explanation is that RXD of AP6502SP-13 is configured as an output somehow during power up. Therefore it could draw high current from MAX232, like a short current. I could not find the data sheet of AP6502SP-13, except this link (https://www.diodes.com/assets/Datasheets/AP6502.pdf). Can you try to flop the logic of R1IN of MAX232 to see if it makes any difference? Regards, Hao
I apologize, because I sent for you the wrong schematic of RXD pin in uC. The correct schematic is shown below:
Analyzing the STM32F030K6T datasheet, it's possible to configure as a RXD pin. Do you mean that is it possible that after reset the pin can became as output?
Thanks for your update. In general GPIO pins should not be set as output after reset. There is no 'default' column in the datasheet either. I'm not sure if it's possible the pins are output during power up. Sometimes as the supply ramps up, the chip is not ready and the output state could be undetermined. There is one more thing you can try. In stead of powering up together, you could power up MAX232 and MCU separately then connect RXD between them.
Analyzing your reply below:
"In stead of powering up together, you could power up MAX232 and MCU separately then connect RXD between them."
I have some considerations:
1) This suggestion can even resolve the issue, but in reality, this is not a usual pratic in projects develpopment, because in a real developmentsituation, I never saw any project that the ICs power supply are done step by step.
2) I believe that the better next step is to test other MAX232 samples to verify if this problem also occurs.
Do you agree?
I have a question for you. Is there another RS232 IC Drivers/Receivers that it can be used instead MAX232?
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