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Thread: Beware! T4x RTC power consumption

  1. #1
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    Beware! T4x RTC power consumption

    Thought I was getting defective CR1220 button cell battery's. However, measuring RTC currents:
    T3.2 1.24uA
    T4.0 30uA

    Doesn't seem like much but with a 35mAH, 20mm dia. coin cell battery that's only 48 days vs 3 years.
    Still great for power failures but not so good for keeping time on intermittent use projects.

    According to IMXRT1060 data sheet an External crystal setup can be lower. Not sure if Teensy board can accommodate that?

  2. #2
    Senior Member+ defragster's Avatar
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    Good info - I had a cell on probably the TallDog T_4.0 board and found it dead - thought I had used a weak battery. Put in fresh and it worked - removed battery when I set them aside assuming perhaps there was high current draw. Getting that current down would be nice if possible. Maybe it deactivates some of the wakeup code the rtc processor can run?

  3. #3
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    Last line of my post above is incorrect. The T4 and T4.1 already have the external crystal. Data sheet Table 4.1.6 suggests 20uA. Not sure why I see 30.

  4. #4
    Senior Member+ defragster's Avatar
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    Correction noted - no easy fix from alternate crystal power - which I misread as just a setting to lower power on the existing use of the crystal.

    The speculation about the rtc low power core being active for wakeup would be interesting is there was a way to disable that to get lower power. But that would involve reading the manual to see if it has an "RTC maintain time only mode" and having that wakeup core more idle ? The more involved wakeup LP core seems unique to the 1062 - where the T_3.x just sleeps only ticking the clock with a less involved wake system that might account for the larger power draw? Though if it suggest 20uA then maybe it is just how the 1062 eats more power.

    Dead battery may have been on T_4.0 beta board as Paul had a cr2032 on one iteration of that ( though probably not as that has more mA and was plugged in mostly ) - TallDog fitted the smaller CR1220. Those T_4.0 beta boards mostly set aside after T_4.1 went beta [last programmed Apr 22 2020 13:11:55] - have not checked the state of the CR2032's still in place lately.

    Just powered and programmed that T_4.0 beta board and indeed the CR2032 is dead - it had the time that survives across Power Off while plugged in - but pulling power and replugging loses the time and the cell measures 0mV

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