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Thread: Does Teensy 4.0 have an analog ground pin?

  1. #1

    Does Teensy 4.0 have an analog ground pin?

    Looking at the pinout diagram, the T4 has a few grounds pins. Is one of them designated as analog ground?

    I need to feed two non differential signals to the two ADCs and would like to know how to design the PCB to minimize noise.

    Edit: alternatively, an external VREFL can also be used for this purpose, connected directly to the ground of the IC that provides the analog signal.
    Last edited by zapta; 10-05-2019 at 04:10 PM.

  2. #2
    Senior Member+ defragster's Avatar
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    T4 does not have separate GND isolation for analog usage. The GND pins are all common.

  3. #3
    On this topic, I've read that there is no external VREFh and there is only one comparison voltage, which is the 3v3 supply source. Is this correct?

  4. #4
    Quote Originally Posted by kjn View Post
    ... there is only one comparison voltage, which is the 3v3 supply ...
    3.3v supply rail is a poor reference for a 12 bit A/D. Hope that there is a better way to provide reference for a 0 - 3.3V analog input range. (In my current application range up to 2.7V would also be acceptable).

  5. #5
    Quote Originally Posted by defragster View Post
    T4 does not have separate GND isolation for analog usage. The GND pins are all common.
    There are three GND pins among the outer pins. Any idea which one is closest (in term of noise) to the MCU's analog ground pads?

  6. #6
    Senior Member PaulStoffregen's Avatar
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    They should all be pretty similar, since layer #2 inside the PCB is a ground plane and the chip has many GND pins.

    But if you had to choose one, I'd suggest going with the GND on the right hand side (next to the Program pin).

  7. #7
    Thanks Paul!

    Regarding vref, what is the best possible vref setup I can use (internal or external)? My signal is single ended and the range 0.5V - 2.5V, coming from a ACS70331EESATR-2P5U3 nearby. My concern is that noise on the 3.3V rail will affect the ADC via vref.

  8. #8
    Quote Originally Posted by zapta View Post
    Thanks Paul!

    Regarding vref, what is the best possible vref setup I can use (internal or external)? My signal is single ended and the range 0.5V - 2.5V, coming from a ACS70331EESATR-2P5U3 nearby. My concern is that noise on the 3.3V rail will affect the ADC via vref.
    I would also like to know if there is a programmable or precision internal vref. I read the 1620 data sheet but it was unclear how the reference function works - or if it was indeed programmable.

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