killed two Teensies

bxwen

Member
I killed two Teensies (4.1) . So I ordered another 10. Hope I can receive them quickly.

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I use digital pins to control max4533 to generate a signal that switching between +25V and -5V. Those In1 In2 In3 In4 are directly hooked up to Teensy digital output. It runs OK for many hours. And then suddenly I couldn't communicate with the Teensy anymore. At this time I see the Teensy board is drawing a lot of current, >400mA, and the FET Q1 becomes very hot.

I think the only way it can be killed is there is some high voltage shows on the digital pin, although I am not sure why. Should I use some resistor between Teensy output and the digital input of the max4533? Or should I put some Zenner diode for protection?
 
If the pins are somehow getting driven with more than 3.3V or negative voltage, a series resistor will help. It still stresses the Teensy pin, but by limiting the current it can really help the build in ESD protection diodes limit the voltage. The higher the resistor, the better it protects. Probably not much point going higher than 10K.
 
I went overboard putting a 50K resistor on each IO pin, and stepping up voltage each day by 5V. So far so good. No more death.
 
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