MKL26Z64VFM4 and custom Teensy LC

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Fyod

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I have begun researching making a custom LC (something I haven't done yet) and some woes have popped up and I could use some input.
For some background - I am making a very low power device requiring a QFN MCU. I had my eyes on the 328p, but I have two UART devices on board and although it can be done, I don't like the idea of sharing the one UART with two devices plus FTDI.

1] Mouser currently only stocks the MKL26Z64VFM4 variant, which seems to only differ in size and pin count. Can this alternatively be used with the bootloader?
According to the datasheet, the QFN32 includes all three UARTs, which is basically all I need, apart from a couple digital pins for LEDs.

2] In terms of parts, I need to shave off as many as I can for space on the board. Can I omit the buffer gate?
Power will be supplied from a battery regulated to 3.3V (everything else is also 3.3V).
Are the 4 caps from 3.3VOUT to the MKL02 important if the MKL02 is not powered directly from the MCU?
Is the cap on VREFH important if the VREF will be omitted?
I read somewhere that the crystal is required.

Any other design considerations are much appreciated!
 
Paul has stated elsewhere that the bootloader ICs look for specific IDs before attempting to load code, so would be suspecting you can't sub in a new micro, though if it is a pinout only change that reports itself as the some device ID then you might be in luck. Can't say that much on removing parts, but believe you can strip out the 5V driver if not required, you can shave out caps if feeling brave, though this depends on what code you run and what power supply - if doing this would suggest leaving room on the PCB at least to start, populate and confirm as working, get final software sorted then measure ripples and see if you can cut them out. General rule is that you always want at least some de-coupling caps to make edge cases less exciting.

You can probably strip all the vref hardware if not going to be used, though check the IC manual for recommended connection for stability and power consumption.
 
Thanks for your advice, GW.

There are three flash/SRAM variants of the chip, three sizes each. I do not need different flash/SRAM, just the different physical size, thus slightly different pinout.
I can't find any info about ID's in the datasheet.
The LQFP (64pin) variant is the one used in Beta boards, I believe, QFN-48 are on the final LC boards, QFN-32 is the one I'm looking at (mainly because its available).
I have remapped the pinout to figure out which pins correspond to the ones broken out on the LC board (thus included in code), thanks to the well-documented datasheet.
I do have decoupling on the 3V3 line, though I'm unsure how important the actual values are.
You're right about the buffer gate, I realised that's for the Neopixel stuff. And I squashed in the crystal and bootloader MKL02, so that should be OK.
 
The bootloader chip is only tested with the NXP/Freescale chips PJRC uses. It *might* work with other similar chips. The only way to find out is actually testing yourself. Or you could try searching this forum... but the of few people I recall who've said they were going to try, I do not recall any conclusive public followups.

Just to be absolutely clear, PJRC doesn't test with any other chips and will not support them if you build a board and it doesn't work. Common sense would seem to suggest building an inexpensive prototype test, right? Maybe even post a conclusive followup here?
 
Thanks, Paul.
I expected this was the case, but asking just in case someone had already attempted to test the smaller variant.
Will follow up with my findings.
 
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