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Thread: Teensy 3.2 at 1.8V (not 3.3V)

  1. #1
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    Teensy 3.2 at 1.8V (not 3.3V)

    All,
    I'm considering a custom Teensy board and intend to get the pre-programmed bootloader chip: IC_MKL04Z32_TQFP32
    from PJRC.
    From the documentation I've scanned; the MK04 bootloader chip runs from 3.3V; however, the freescale documentation seems to indicate that the chip is capable down to 1.7ish volts.

    In my application; I need the Main Teensy chip (MK20DX256) to operate with a 1.8V signal level. I couldn't easily locate any "de-rateing" details in the Freescale documentation regarding running at lower 1.8V conditions.

    Assuming I use voltage translation between MKL02 and MK20 would there be any issue running the MK20DX at 1.8V?
    Does the bootloader chip make any assumptions about the voltage system?
    Could the bootloader run at 1.8V as well; thereby negating any need for voltage translation?
    John

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    Apply 1.8V to 3.3V and try it.

    Of course when you attach a USB the whole thing we be brought to 3.3V

  3. #3
    Senior Member PaulStoffregen's Avatar
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    I've done very little 1.8 volt testing. In fact, pretty much none at all.

    But from Freescale's documentation, the main issues are USB and SPI faster than 12 Mbit/sec.

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    Quote Originally Posted by PaulStoffregen View Post
    I've done very little 1.8 volt testing. In fact, pretty much none at all.

    But from Freescale's documentation, the main issues are USB and SPI faster than 12 Mbit/sec.
    Ok. I understand - Most uCs are 3.3V at best; so 1.8V is a stretch.
    Good data about the SPI; but USB? Can you point me to the document /page regarding USB?

    My assumption is that you can put VBUS in at VRegIn... and the USB PHY would operate at 3.3V. But if the documentation says something different; then maybe I need to rethink my plan.

  5. #5
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    Well USB supplies 5V so you can just use that to power the device up to 3.3V so you don't encounter any issues when communicating with a computer.

    The data lines of USB are expected to be 3.3V. If your device isn't supplying that it won't operate

  6. #6
    Just wanted to bump this thread if there was any development? I'm also developing an ultra low power solution based on Teensy. 3.2
    Looking at the data sheet I found the following diagram which leads to conclude that what you propose can work just fine. I assume?! that the USB controller will work internally at 3.3v while the VDD and board will remain at 1.8v.

    Were you able to find any de-rating information? 12MHz is fine for SPI, my sensors top out at 10 anyway.
    Can you run the processor at 72MHz@1.8V. Looking at the crummy graph in the electrical manual 72MHz gives the best mA/MHz ratio. Which leads to best power savings If you can get optimized code with little delays.

    I will be investigating this more and report back.

    As a side note. You could also power the MKL02 chip from the VOUT33 line. Thus. The MKL02 is completely off when USB is unplugged. Or wait, that would overload the MCU 1.8v pins. Hmm.


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