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MAX232: MAX232 overheat

Prodigy 140 points

Replies: 23

Views: 1245

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

  • Hi Sergio,

    The datasheet for this part recommends using 1-uF capacitors for the charge pump circuit. Can you try using those instead and see if it resolves the heating issue? With the smaller capacitance I am concerned that maybe the charge pump needs to switch too frequently, resulting in increased power dissipation in the device.

    If that does not resolve the issue, then it would be good to understand what application conditions exist when the issue occurs. For example, does it occur at power-up or later on during normal operation? If during normal operation, does it correlate to a certain DOUT condition like driving high, driving low, or switching? It would also be useful to probe some relevant signals on an oscilloscope like the logic IOs, the RS-232 signals, and the power rails (V+/V- as well as VCC).

    Regards,
    Max
  • In reply to Max Robertson:

    Hi Max,

    Thank you for your help.

    I followed your recommendation to change the capacitors for the  charge pump circuit from 100nF t0 1uF. I did 6 tests to read the smart card . In the 5 try, occured the overheat and the circuit stoped to work. I powered off the circuit and I did the 6 try. In this case, didn,t occur the overheat and the circuit worked as expected.

    Below is the schematic of the supply circuit to MAX232. It is supplied trough a microcontroller enable signal in the read smart card operation. So, the issue occurs after the power supply circuit is enabled.

  • In reply to Max Robertson:

    Hi Max.

    I have another question about this issue. You told me that the capacitors for the charge pump circuit must be of 1uF. My question is if the capacitors between C1+ and C1- and C2+ and C2- also must be of 1uF.

    Best Regards

    Sergio Fink
  • In reply to Max Robertson:

    Hello Max.

    Bellow are the wave form of pins 2 and 6 of MAX232 in NO OVERHEAT state and in OVERHEAT state:

    NO OVERHEAT STATE: PIN 2 = 9,2V

    PIN 6 = -8,2V

    OVERHEAT STATE: PIN 2 = 3,4V

    PIN 6 =1,8V

    Best Regards

  • Genius 17515 points

    In reply to Sergio Fink:

    Sergio,

    Thanks for your information. If changing the capacitors doesn't help but power cycle does, we may need to take another look at your power design. When overheat happens, is it possible to measure the voltage and current output of Q401? Or you could capture the waveform of MCU enable and power ramping up. BTW, when you enable the read smart card operation, what's the states of MAX232, like is there signal on RS-232 bus?

    Regards,

    Hao

  • In reply to Hao L:

    Hello Hao,

    How are you?

    Answering your question, in the overheat state the voltage is 5V and the current is 530mA. In no everheat  state  (normal operation)  the voltage is 5V and the current is 75mA.

    Best Regards

  • Genius 17515 points

    In reply to Sergio Fink:

    Sergio,

    Thanks for your data. Have you ever been able to check the ramp up voltage/current plots? I suspect sometimes somehow during power up, the device draws too much current from the supply and locks the system in a high current state.

    Regards,
    Hao
  • In reply to Hao L:

    Hao.

    Below is the voltage wave form during power up. Unfortunately we can't provide the current wave form because we don't have a current probe point for osciloscope.

    Regards

    Sergio

  • Genius 17515 points

    In reply to Sergio Fink:

    Sergio,

    Thanks. Several more questions: if you power cycle the overheat devices (maybe several times), are the devices always able to work normally? Have you ever tried with L400 shorted (connecting Vcc_smart and 5V directly)? Is MAX232 powered by Vcc_smart for 5V? What's MAX232 T1OUT pin's load during power up? Is TXD high or low? Can you test with the load removed or setting TXD in other state?

    Regards,
    Hao
  • In reply to Hao L:

    Hao,

    Answering your questions:

    1) if you power cycle the overheat devices (maybe several times), are the devices always able to work normally?
    R: Yes

    2) Have you ever tried with L400 shorted (connecting Vcc_smart and 5V directly)? Is MAX232 powered by Vcc_smart for 5V?
    R: Yes. But the result is the same.

    3) What's MAX232 T1OUT pin's load during power up? Is TXD high or low?
    R: TXD is in 240mV

    4) Can you test with the load removed or setting TXD in other state?
    R: When I removed the load of TXD pin, the overheat occurs and the voltage is the same (240mV)

    Regards

    Sergio

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