Deep Sleep with RTC Wakeup

[_Dejan_]

Hi, Im new here and microcontroller programming... I curently waiting nrf52840 PDK so Im only quick read SDK and documentation... Before Im program only devices with .NET Micro Framework and make a lot of applications for computers, but this is different world :) So here is question: Is possible wake up device by RTC Event? For example put device(battery powered) in deep sleep for 10 minutes(disable all peripherals to increase battery life) and after that time wake it up? Thanks for answer.

[Jørgen Holmefjord]

Hi,

There are two low-power modes in the nRF52840; system on and system off mode, where system off mode is the deepest power saving mode the system can enter. When the device have entered system off mode, the only possible wakeup sources are reset, GPIO, NFC, USB or LPCOMP modules. A wakeup from this state, will trigger a reset of the device. It is not possible to wakeup from system off mode using the RTC.

In system on mode, the RTC can be used as a wakeup source. The downside of this, is the increased current consumption of system on mode, compared to system off mode. An alterantive for devices requiring long deep sleep times, could be to use an external low-power RTC that can can set a GPIO to wake the device.

Best regards,

Jørgen

[_Dejan_]

Hi Jørgen,

Thanks for answer. I have only one quick question

Can you tell me approximately difference in power consumption System Off vs System On with RTC(turning everything off except RTC)?

For example:

System Off 0.4µA

System On with RTC cca. 1µA

Thanks for any info.

[Jørgen Holmefjord]

This can be calculaed from the values in the product specifications:

System ON base current, no RAM retention: 0.7µA

Run current Real Time Counter (LFCLK source): 0.1µA

Run current 32.768 kHz crystal oscillator: 0.23µA

Run current 32.768 kHz RC oscillator, Normal mode: 0.7µA

Run current 32.768 kHz RC oscillator, Ultra-low power mode: 0.2µA

The total current consumption, depending on your LF clock source:

System ON, no RAM retention + RTC + LFSRC = 0.7µA + 0.1µA + {0.23, 0.7, 0.2}µA = {1.03, 1.5, 1.0}µA

If you need RAM to be retained in System On mode, you have to add an additional 30nA per 4kB RAM block that is used.

[_Dejan_]

Thank you very much for all your answers :)

[UBAN]

Hi,

According to nRF52840 Product Specification v1.1, "System ON base current, no RAM retention: 0.7µA" is not described.

Does "System ON, no RAM retention, wake on any event" mean "System ON base current, no RAM retention"?

If the meanings are the same, is the following correct?

System ON, no RAM retention, wake on RTC (running from LFRC clock) = System ON, no RAM retention + RTC + LFSRC =0.97uA + 0.7uA + 0.1uA =1.77uA

Best regards,

uba

[Jørgen Holmefjord]

Yes, it is the same. You can see current consumption for the scenario that you are asking (I_ON_RAMOFF_RTC) in this table.