Custom Teensy 4 Schematic Review

ctadlock

ctadlock

Active member
Im building a custom board based on a Teensy 4. We heavily use the Teensy 4.0 and 4.1 in our other projects but for this project we need a very small form factor and a limited number of exposed pins to talk with another chip via SPI and a couple other GPIOs. Ive read through countless forum posts, the power up sequence and all the other project schematics I could find and I think I have it, but need some other experienced eyes on it.

Notes
- 4 layer, 1.2 mm thick
- USB power only, no external power or VBAT
- No need for RTC so no 32.768 crystal
- No need for ONOFF
- Program switch
- BUILTIN LED on NXP chip (same as Teensy)
- LED on bootloader (same as Teensy)
- Hardware serial for logging
- SPI1
- Couple GPIO (not connected or shown)

I appreciate any feedback!
 

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Thanks for taking a look Paul.

I'm not sure I understand your comment. Are you referring to the 5V-3.3V LDO? If so it seems well able to handle the current as its rated to 1A. The part is NCP692MN33T2G.


It's also being used on jenschr's board.

github.com

Teensy-4.1-example/Teensy4.1-example.csv at main · jenschr/Teensy-4.1-example

Kicad files to make a custom Teensy 4.1, based on the official Teensy schematics. Tested and verified. - jenschr/Teensy-4.1-example
github.com github.com

Maybe I'm missing something?
 
The NCP692MN33T2G data sheet says that heat will be dissipated from the GND connection through the copper of the PCB.
Paul is making you aware that this TINY voltage regulator may heat up with 100mA current flowing. This heat will have to be dissipated through the copper or the regulator may start turning off.
 
This DFN part looks much better, and should be similar to what's on Teensy 4.0.


1737635993642.png


My quick lookup probably found a different package, with alarmingly high 277.

Still, you should pay attention to how much the thermal performance changes depending on how much exposed copper area is used.
 
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