RAK12002 RTC power consumption

WisBlock
1

I spent the day chasing uA for a current project. The project is RAK4631 deep sleep base.

In my project, i am using the 12002 rtc, to wakeup the 4631 from deep sleep via an interrupt and awake the rtc provides timestamps for my stored measurements.

Using a RAK4631/19007 the lowest current i can get is around 13.5uA. This matches other post in this forum.

Based on my testing, adding the RAK12002 rtc (slotD) consumptions is approximately 45uA.

The RAK12002 is consuming 32uA, just being connected, with no activity, and with the CLK/INT lines configured as INPUT (no pullups).

FYI, I am open to suggestions, if you think the 12002 current can be reduced.

Otherwise, i hope this helps anybody considering the RAK12002 for low power apps.

2

Datasheet says 45nA consumption, but it is not clear when this is valid.

I can confirm your findings when powering with 3.3V that the consumption is in the uA area. But I see lower values when I switch off all features of the RTC like the clock-out pin.

Custom Base Board with single 3.3V supply gives me ~7uA consumption for the RTC, LoRaWAN class A, connected to server, 10 minutes send interval.

~30.8uA with RTC

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and ~23.8uA without the RTC.

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Initialization of the RTC:

	rtc.initI2C(Wire);

	// Direct Switching Mode (DSM): when VDD < VBACKUP, switchover occurs from VDD to VBACKUP
	rtc.writeToRegister(0x35, 0x00);
	rtc.writeToRegister(0x37, 0xB4); 

	// Disable timers
	rtc.writeToRegister(0x0A, 0x00);
	rtc.writeToRegister(0x0B, 0x00);

	// Disable clock output
	uint8_t reg_value = rtc.readFromRegister(0x0F);
	reg_value = reg_value & 0b11111011;
	rtc.writeToRegister(0x0F, reg_value);

	// Disable interrupts
	reg_value = rtc.readFromRegister(0x10);
	reg_value = reg_value & 0b00000010;
	rtc.writeToRegister(0x10, reg_value);

	// Disable Clock Interrupts
	reg_value = rtc.readFromRegister(0x12);
	reg_value = reg_value & 0b00000000;
	rtc.writeToRegister(0x12, reg_value);
3

And, as I guess the question will come up, the Base Board I use is from our RAK10702 Indoor Comfort.

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4

Hi all,

Interested to know if there was any conclusion here. Asking because normally one would use the RTC to create extremely low power solutions but if the RTC itself is consuming too much power then this defeats the whole purpose ! I would expect to have a solution consuming not more than 10uA when fully sleeping based on a RAK3372 with an RTC.

Thanks,
Serge

5

Hi all, I came for the same, what is the issue here? is something implicit in the RAK 12002 that keeps it consuming a lot of power?

6

With WisBlock, the best power consumption with a RAK3372 you can achieve is ~20uA
This is with an empty WisBlock Base Board.
The reason is

  • UART-USB chip CH340 not powered down (main reason)
  • I2C pullups on the Base Board
  • resistor divider on the battery voltage input
7

Thanks for the reply Bernd,

Does RAK have any plans to make design improvements to address this in the future ?
Goes along the same lines as my other post regarding the choice of charging IC.

Kind thanks,
Serge

8

We have an idea for the RAK3372 to lower the sleep consumption, but not sure when it will be implemented.

We have as well a prototype of the RAK19007 with a different charger, temperature controlled charging and some other improvements. Again, not sure when it will be available.