M5Paper power management



  • There is a potential issue with M5Paper power management.
    SY7088 boost regulator is used to generate a stable 5V voltage used used for all other voltages.
    0_1607020633850_9454cec4-4c48-4bd6-9b65-8fbe64c140a3-image.png
    When the system is in power save and power off modes, resistors R30 & R33 values causes the constant current consumption of ~254 uA which leads to quite rapid battery discharge. At least 10x higher values should be selected. From Data sheet:

    it is desirable to choose large resistance values for both
    R30 and R33 . A value of between 10kΩ and 1MΩ is
    recommended for both resistors.
    

    Furthermore, SY7088 shuts off the output only at ~2.3V which couses battery overdischarge!



  • Hello @loboris

    if I read the schematics correctly in power off mode signal PS_ON is low, FET2 open, PWR_EN pulled up by R35, FET1 open, VBAT zero and VSYS zero as well, therefore the values of R30 and R33 shouldn't matter since SY7088 is without power. Or am I missing something?

    BTW: The RTC will drain the battery even lower as it is directly connected to the battery and runs until 1 volts.

    Thanks
    Felix



  • @felmue said in M5Paper power management:

    Hello @loboris

    if I read the schematics correctly in power off mode signal PS_ON is low, FET2 open, PWR_EN pulled up by R35, FET1 open, VBAT zero and VSYS zero as well, therefore the values of R30 and R33 shouldn't matter since SY7088 is without power. Or am I missing something?

    BTW: The RTC will drain the battery even lower as it is directly connected to the battery and runs until 1 volts.

    Thanks
    Felix

    Thank you, I've missed that.
    RTC current is <1uA, so it should not be a problem.



  • Hi @loboris

    you are of course correct about the RTC current - it will take a very long time to drain the battery. BTW: I am currently experimenting with an M5CoreInk and in shutdown mode I am measuring 2.6 uA at the battery.

    Cheers
    Felix



  • Hi guys,

    Being a beginner in electronics, I am wondering how to make current measurements with such low intensities (µA). Would you be so kind as to explain to me how you do it and with which model of measuring device. Pictures are welcome if it doesn't take too much time.

    Thanking you in advance
    Steph



  • Hello @m1cr0lab

    I am using a uCurrent Gold Multimeter Adapter from EEVBlog.

    Cheers
    Felix



  • Thank you very much @felmue,

    Then I actually saw that you were using this device on your M5Stack page.

    Thanks again for your advice, which I think is perfect... hopefully we can still find some in stock somewhere.

    Regards,
    Steph



  • Hello again @felmue,

    I came across this Adafruit video today, and I thought maybe you'd be interested?

    https://youtu.be/m0XAT8V37-g?t=412

    (The interesting part is between 6'52" and 13'05")

    => Power Profiler Kit II

    Cheers
    Steph



  • In case of ESP32 you can measure power consumption with practically any multimeter in uA range.
    If the current is < 5-10 uA you have an excelent low power device.
    You will rarely need the information about power consumption in sub uA range and investing any amount in a device for measuring current of ESP32 deep sleep mode is probably waste of money (unless you need it for other measurements, of course).



  • Hello @m1cr0lab

    thanks for sharing. I appreciate it.

    I don't remember the brand or name of the device, but I've seen something similar to the PPK II before where the current was sampled for a while to get a better idea of the total power consumption over time - let's say from waking up from deep sleep to going back to deep sleep.

    Thanks
    Felix