DS3231 High Power Consumption

Other Hardware General Electronics
1

Hello!
I would like to make battery powered Arduino.
The standalone Arduino draws 2uA (power down) but when I use the DS3231 I get 100uA.
DS3231 is powered by Atmega PIN that I digitalWrite LOW in order to sleep it. I check with multimeter and it is OK the ON-OFF of the pin.
Here is the schematic. What goes wrong?
Thank you!

schematic.jpg
schematic.jpg1573×703 111 KB

2

How does the DS3231 keep time for you if you don't have battery back up for it?

If you don't have VCC applied to the chip, it can be powered thru the control lines that are high.

3

The data sheet gives the maximum Vbat battery current for a DS3231 as 70-150 uA (depending on the voltage).

4

You need to attach the pull-ups for the I2C bus and SQW to the switched Vcc, not +3V3.

5

jremington:
The data sheet gives the maximum Vbat battery current for a DS3231 as 70-150 uA (depending on the voltage).

That's the I2C active current, not the timekeeping current.

6

That's the I2C active current, not the timekeeping current.

Correct, but it is not clear from the OP that the conditions for "timekeeping" are met. These are: EOSC = 0, BBSQW = 0, SCL = SDA = 0V or SCL = SDA = VBAT

7

DS3231 is powered by Atmega PIN that I digitalWrite LOW in order to sleep it.

Try to set PIN as input (no pullups there) to sleep it..

8

pito:
Try to set PIN as input (no pullups there) to sleep it..

Setting it LOW will prevent it from floating and triggering anything else...

Remember the pull-up resistors must derive from the switched pin, not the main 3V3,
otherwise you lots of leakage through them. The I2C bus must be powered down
too of course (SCL & SDA LOW).

9

R9, R2, R3 = 100ua
Dwight

10

dwightthinker:
R9, R2, R3 = 100ua
Dwight

Huh?

11

R9 has a 0 out of the DS3231, that is 33ua
R2 and R3 have one end at 0 the other at 3.3v
another 66ua.
That sounds like his missing 100ua.
Dwight

12

Wire the R2 R3 R9 to PD7 (your RTC-VCC), instead to 3.3V.

Let R9 connected to 3.3V in case you want to wake up the cpu via SQW/INT signal. You may try to increase the R9 to 100k.

Then you should have measured something like:
2ua (your "standalone arduino" in power-down) + 33uA (via R9=100k with SQW/INT low) = 35uA max.

With R9 = 1Meg you may get 5uA max.

PS: I doubt you can get 2uA with an "arduino". You may get that with baremetal atmega328p chip, a voltage regulator with 1uA questient current, no resistors on pins, no pullups enabled, no timer or wdt running, BOD disabled, ADC disabled, power-down mode, ceramic capacitors, no leds lit.. :slight_smile: So it is my understanding your "standalone arduino" is a baremetal chip with crystal and the ds3231 as depicted on your schematics above.. But that is not an "Arduino" anymore :slight_smile:

dwightthinker:
R9 has a 0 out of the DS3231, that is 33ua
R2 and R3 have one end at 0 the other at 3.3v
another 66ua.
That sounds like his missing 100ua.

That is ~1mA not 100uA (10k||10k||10k at 3.3V is 990uA).

13

Oops, misread my calculator.
1ma. is correct.
Dwight