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IC's Blowup internally (multiple examples)

Bart Winter
Prodigy 10 points
Part Number: TRS3232E
Other Parts Discussed in Thread: MAX232, TRS3232

Tool/software:

I designed a PCB with a "standard" MAX232 converter, in this case the TRS3232EIPW.

Used the circuit numerous times to convert the serial RS232 signals to the uC signals.

When the PCS where tested an configured there where no faults and/or errors.
However a few years/months later we received a batch of units out of the filed from which the configuration could not be changed. Normally the interface is not used and is not connected.

After examining the units with the serial problem we see all units have similar problems with the TRS3232 IC, it has black exploded pins and is locally overheated.
The pins of the voltage doubler or negative buffer with attached capacitors always seem to be affected.
After blowup negative voltage is no longer available en sending fails (no V-) but receiving remains working.

Any ideas why this IC fails on this board?

  • 0
    Guru 316470 points

    Probably overvoltage or overcurrent.

    Are those CON_RFID connections reachable? ESD is unlikely with those large capacitors; I'd guess they were shorted.

  • 0
    TI__Guru 72221 points

    Hi Bart,

    Bart Winter said:
    However a few years/months later we received a batch of units out of the filed from which the configuration could not be changed.

    Not sure if this is relevant but the top markings in your picture seems to indicate the device was created in 2018 of January.

    Bart Winter said:
    After blowup negative voltage is no longer available en sending fails (no V-) but receiving remains working.

    So the receiver pins on the RS232 side have higher absolute max ratings than the drivers (section 6.1 in datasheet), it could be possible a voltage higher than 13.2V appeared on the RS232 pins but lower than 25V which could have damaged the drivers but not the receivers. 

    The pictures look like there may be some dark liquid/substance on the pins. Do you know if that's the device's plastic that melted or is it possible a liquid could have spilled onto the PCB and shorted some of the pins/pads? 

    The external ESD device looks like it should trigger at a minimum of 14V, likely has more margin to trigger earlier so I don't necessarily think it's from an ESD event. 

    Is there any chance that one of the driver connector pins could of shorted to a higher voltage power rail?

    -Bobby