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Thread: Teensy 4.0 at 24Mhz still drawing 100mA. Why?

  1. #1
    Junior Member
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    Nov 2021
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    Teensy 4.0 at 24Mhz still drawing 100mA. Why?

    Hello Teensy folks!

    I have a teensy 4.0 with an audio-shield (rev D) and I would like to build a reverb euro-rack module with them. So far, I'm testing with the example code that uses a freeverb node.

    I'm powering it at 5V. I noticed that at 600Mhz it would draw over 180mA and when clocking it at 24Mhz, it would still draw around 100mA. I'm very confused why this happens as it is suggested that power-consumption should be less than 10% of that.

    I measured it by putting my multimeter in series with the 5V line. I tried both the 5V line from my eurorack synthesizer, which can only supply 100mA. So initially when running the teensy at 600Mhz, it would fail after 20 sec because the voltage regulator couldn't take it anymore. Now I'm testing with USB and I also tested it with a L7805 connected to the 12V line to give me 5V.

    I verified that the teensy is working. I've been experimenting with it and I would not be super surprised if I damaged it in some way, but that doesn't seem to be the case. I was hoping that at 24Mhz, power consumption would be much lower (say around 30mA).

    Can it be that the audio shield is drawing a lot of current? Not sure if I can test it without, because the code does depend on it.

    Some help would be highly appreciated!

  2. #2
    Senior Member
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    Those current values are as expected with the current libraries.

    Power optimization is on the list I believe, but Paul has many other more pressing issues on the list IIRC. The iMXRT1062
    is a complex chip (datasheet is 3437 pages...) Running the processor at 24MHz does not imply there aren't PLLs running
    much faster on the chip and clocking other subsystems - note that its designed to talk to high speed interfaces in hardware
    using DMA whether or not the processor is currently halted, clocked at 600MHz, 24MHz or whatever, so much of the chip is
    not in the CPU clock regime.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    As a quick test, I just powered up a Teensy 4.1 (previously programmed with default 600 MHz settings) without any other circuitry and no USB cable, just a 5V power supply. My power supply current display says 103 mA.

    Normally the audio shield should not need 80 mA. Maybe other circuity is connected?

  4. #4
    Senior Member
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    I measure on the T4.0 (albeit with a fairly crude USB current sensor I made):

    Code:
    freq  aud-adapt current
    24      no      60mA
    24      yes     70mA  - not using adapter
    150     no      80mA
    600     no     100mA
    600     yes    125mA  - using adapter + heavy CPU usage
    Last edited by MarkT; 01-06-2022 at 02:10 PM.

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