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MAX232: MAX232 overheat

Prodigy 140 points

Replies: 23

Views: 1277

Part Number: MAX232

Hello people,

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?

Best Regards

  • In reply to Sergio Fink:

    Sergio,

    Do you mean TXD (T1IN) pin is 240mV during power up? If nothing is connected to T1IN, does it stay at 240mV? What's the voltage of T1OUT? Could you monitor the voltage of these two pins during power up? Do you still see any difference between normal and overheat?

    Regards,
    Hao
  • In reply to Hao L:

    Hello Hao.

    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.

    Best Regards

  • In reply to Sergio Fink:

    Sergio,

    Is AP6502SP-13 powered up the same time as MAX232? Does MAX232's supply have anything to do with AP6502SP-13? After you disconnect R1OUT from AP6502SP-13, do you still see overheat?

    Regards,
    Hao
  • In reply to Hao L:

    Hello Hao.

    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.

    Best Regards

    Sergio Fink

  • In reply to Hao L:

    Hello Hao.

    Sometimes even with the R1OUT pin disconnected, the R1OUT  signal occurs as the picture bellow:

    Best Regards

    Sergio Fink

  • In reply to Sergio Fink:

    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

  • In reply to Hao L:

    Hao,

    Good morning.

    I apologize, because I sent for you the wrong schematic of RXD pin in uC. The correct schematic is shown below:

    Best Regards

    Sergio

  • In reply to Hao L:

    Hao,

    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?

    Best Regards

    Sergio

  • In reply to Sergio Fink:

    Sergio,

    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.

    Regards,

    Hao

  • In reply to Hao L:

    Hao,

    good morning.

    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 development
    situation, 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?

    Best Regards

    Sergio

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