M5Paper power management

loboris

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!

felmue

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

loboris

@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.

felmue

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

m1cr0lab

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

felmue

Hello @m1cr0lab

I am using a uCurrent Gold Multimeter Adapter from EEVBlog.

Cheers
Felix

m1cr0lab

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

m1cr0lab

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

loboris

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).

felmue

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

Dominic

Hey I am thinking about buying the m5paper and I hope someone here can answer my question.
How much current does the board use in sleep?
Or maybe the more important question is the following.
If I want to develop something like a weather station. And update the display once every 10min, 30min or every hour. And between that the device is sleeping. How long could the battery last?
I don't want exact figures. What I need is some rough estimate like 1week, 1month or whatever.
Would be great if someone knows more and can help