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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?
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In reply to Max Robertson:
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.
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
In reply to Sergio Fink:
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?
In reply to Hao L:
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.
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.
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)
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