Teensy 4.0 burning out... how do I find out what the problem is?

[addy_electronix]

Hey guys! I apologize if I might miss a guideline or detail in this initial post as I am new to hobby electronics and this forum as a whole, but I have been running into a couple of issues with a Teensy 4.0 in a design that involves a RF module for remote control, a MOSFET switch and 3 servo motors. This is the schematic for my circuit:


I tested the current draw to the SIG pin of the MOS module from pin 0 of the Teensy 4.0. It is near 0A and I would assume so, since the SIG pin is connected to the gate of the MOSFET. The reason for the MOS module is so that I can switch off power to the servo motors once I am done with whatever I need to do while still keeping the Teensy on in order to conserve battery power. The Teensy 4.0 is powered with the use of a 5-6V power bank connected to the USB input which was represented on the schematic as a 4 cell input to the Vin pin. Another source of issues could be the connection between the RF module and pin 29. I am unable to tell what might be causing the issue.

I have burned out 2 Teensy 4.0s so far, and I am assuming that they are burned since my laptop cannot recognize them through the USB port and all the LEDs are off. The chip heats up a fair bit on one of them. Does this indicate for sure that they have burned out? Both of them still have a 5V output from that specific pin when plugged in, though the 3.3V output pin only gives 0.2 to 0.4V. What does this mean in the context of the electrical connections? Can it be fixed in any way? Also, is there any way to tell which pin specifically burned out... and how would one digital pin affect the rest of the board? I tried looking at the electrical connections on the datasheet, but I am too novice to be able to diagnose the issue without more guidance. I would really appreciate any help on this and do let me know if I need to add more details to my post. Thanks!

 

[KenHahn]

Looking at your diagram, I notice a few possible issues.

The maximum allowable voltage on the VIN pin that feeds the RT1060 CPU chip and 3.3V regulator is 5.5V. When you say a 5-6V power bank, you may be damaging those chips through over-voltage if it is running over 5.5V. If that is the case, you could put a silicon diode in series to help drop this voltage down to a safer level.

The RF Module power is labeled as 5V, but you show it connected to the Teensy 3.3V. If it is expecting 5V, it may be putting excessive load on the 3.3V regulator on the Teensy. If the RF module can operate at 3.3V, then you'd want to make sure the current draw doesn't exceed the 250mA limit of the regulator on the Teensy. If the RF module is actually running at 5V and the drawing is in error, then the logic level output on pin 29 would be 5V and would damage the Teensy assuming this is an input pin on the Teensy and not an output. Usually if you over voltage an I/O pin, it will just damage that pin and not the whole module.

The IRF520 MOSFET doesn't work well with 3.3V logic. It is barely 5V logic compatible, so it won't be turning fully on and will act more like a resistor and drop your 6V for the servos down to something lower and may heat up, but it won't damage the Teensy.

Driving the control lines of a servo at 3.3V may or may not work depending on the servos you are using, but most can work down to a 3V input signal. Again, I wouldn't expect it to hurt the Teensy even if the servos weren't happy about it.