Power optimisation help

RE: Power optimisation help

Gary T — Fri, 10 Jun 2022 14:34:46 GMT

Thank you!

RE: Power optimisation help

Sigurd — Fri, 10 Jun 2022 11:24:15 GMT

[quote user="Gary T"]Now I am achieving an average power usage of 20µA and a sleep power usage of 3.4µA which is fine for its intended purpose.[/quote]

Great!

[quote user="Gary T"]I haven't yet found any default settings for the external crystals. Can someone let me know what the default settings are and whether I need to specifically enable them myself?[/quote]

Default setting is to use the LF crystal. https://github.com/nrfconnect/sdk-zephyr/blob/v2.7.99-ncs1/drivers/clock_control/Kconfig.nrf#L31

For boards that does not have LF crystal, set CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

RE: Power optimisation help

Gary T — Fri, 10 Jun 2022 11:04:39 GMT

Here is another update on my project.

I am very happy to let you know that I managed to get the power levels on the dongle much lower.

The culprit was the SHT31 temperature/humidity sensor, or more specifically, the Zephyr driver for that sensor. Turns out the sensor has 2 modes of operation which include "single shot mode" or "periodic acquisition mode". The Zephyr driver defaults to the "periodic" mode and this creates a constant current draw of around 45µA. When I changed it to "Single Shot" mode that constant 45µA goes away.

Now I am achieving an average power usage of 20µA and a sleep power usage of 3.4µA which is fine for its intended purpose.

I can also see that the DC/DC is defaulted "On" in the Kconfig file located in the Zephyr Boards directory.

# nRF52840 DK NRF52840 board configuration

# Copyright (c) 2016 Nordic Semiconductor ASA
# SPDX-License-Identifier: Apache-2.0

if BOARD_NRF52840DK_NRF52840

config BOARD_ENABLE_DCDC
bool "Enable DCDC mode"
select SOC_DCDC_NRF52X
default y

config BOARD_ENABLE_DCDC_HV
bool "Enable High Voltage DCDC converter"
select SOC_DCDC_NRF52X_HV
default y

endif # BOARD_NRF52840DK_NRF52840

I haven't yet found any default settings for the external crystals. Can someone let me know what the default settings are and whether I need to specifically enable them myself?

Regards

Gary

RE: Power optimisation help

Gary T — Wed, 08 Jun 2022 12:29:00 GMT

Quick update on my progress with this.

I have managed to find the following blog post which contains a lot of good info around power optimisation on Zephyr https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/optimizing-power-on-nrf53-designs.

I also used the attached project to a comment on that post to further see how to implement some of the steps. (The project no longer compiles as some of the functions/API's have changed but I managed to get it working. You may want to consider updating it.)

I am still working my way though all the steps detailed in the blog post but I managed to get the Blinky App on the nRF52840 Dongle into a very low power state.

To start with I cut SB2 and soldered SB1 on the dongle and I then added

#include <pm/pm.h>

#include <pm/device.h>

to the main.c file and this reduced the sleep power usage to 3.27µA.

If I then add pm_power_state_force(0, (struct pm_state_info){PM_STATE_SOFT_OFF, 0, 0}); after a few repetitions of the blink then the power usage goes down to 0.39µA. This clearly shows me how low power the dongle is cable of going.

This answers the "Scenario 1" in my post above.

I tested the dongle with my custom BT Beacon app and the power usage went down to 66µA average and 41µA when "sleeping". This is 20µA lower than my previous measurements. I haven't managed to get it lower yet. I would like to get the sleep current to around the 3.3µA (same as the Blinky App) or lower.

I am still confused about why the sleep current on the DK is 4.6µA but 41µA on the dongle? Since I now know that the dongle is capable of very low power usage what could be running on the dongle that isn't being measured on the DK?

I will continue to apply the steps from the blog post and see if they make any difference. I would still appreciate feedback to my questions above please.

Regards,

Gary