I have a real puzzler here.
I have a PCB board designed with a few TLC5940 chips daisy-chained to a T4. I've used these boards many times before.
When run on the board, the Teensy gets extremely hot. According to tempmonGetTemp(), the internal junction temperature reaches 90C.
Now here's the puzzler. I put the T4.0 on a breadboard and connect it to my PCB using jumper wires. Now it runs fine, around 68C.
Ok, I think maybe there's a bad connection on one of the pins causing a stray current, or something. I remove all the pins from the T4.0 except the ones I need, so the electrical connections are exactly the same as when I used the jumper wires, except now the T4.0 is back on the board.
It still overheats!
So I think, okay, maybe it's the components nearby heating up the Teensy. But the components are a good distance away, certainly nowhere near close enough to get the Teensy's junction temp to 90C, and the entire board is not warm—it's just the ARM processor in the middle heating up, the heat is definitely coming from the Teensy itself.
The BJTs in the center, underneath the Teensy, are on the opposite side of the board and do not get hot.
What in tarnation is going on?! I'm at a complete loss.
Here's my board design.

I have a PCB board designed with a few TLC5940 chips daisy-chained to a T4. I've used these boards many times before.
When run on the board, the Teensy gets extremely hot. According to tempmonGetTemp(), the internal junction temperature reaches 90C.
Now here's the puzzler. I put the T4.0 on a breadboard and connect it to my PCB using jumper wires. Now it runs fine, around 68C.
Ok, I think maybe there's a bad connection on one of the pins causing a stray current, or something. I remove all the pins from the T4.0 except the ones I need, so the electrical connections are exactly the same as when I used the jumper wires, except now the T4.0 is back on the board.
It still overheats!
So I think, okay, maybe it's the components nearby heating up the Teensy. But the components are a good distance away, certainly nowhere near close enough to get the Teensy's junction temp to 90C, and the entire board is not warm—it's just the ARM processor in the middle heating up, the heat is definitely coming from the Teensy itself.
The BJTs in the center, underneath the Teensy, are on the opposite side of the board and do not get hot.
What in tarnation is going on?! I'm at a complete loss.
Here's my board design.
