Teensy power feed issue - boot issue

[tf3t]

Hi

I'm using this Teensy 3.2 to control a device I'm building.

Arduino compile with the Teensy addon.

Everything is going fine, but

#1: works with a fixed linear supply - if I turn on the DC everything OK

#2: If I power on from a 3.2A switch mode supply (Meanwell) Teensy does not boot.
- if I press the reload button on the Teensy it will boot up.

3: If I disconnect the DC supply with a jumper - turn on the power supply, then connect the jumper Teensy boots

I measured the 12V and 3.3v ramp up time and it's about 15ms, actually the 3.3v is bit faster.

I included a youtube upload that shows this

any ideas ? - I put a "delay" in the startup of the code - but that did not help.

- Benni

 

[tf3t]

well, after some troubleshooting, I found out that If I connected the bottom 3v3 input as well this stopped. I measured that pin with a scope before I connected it and it rose to 3v3 in 4ms. So powering the Teensy only from one 3v3 pin is perhaps not enough ? don't quite understand what is going on here. (thin PCB trace ?)