High current during WFE with nRF52832

RE: High current during WFE with nRF52832

eBrock — Fri, 25 Oct 2019 15:19:32 GMT

Ahh, OK, that makes sense now. Thanks for explanation.

My application will use the radio periodically, so I need the HFXO.

RE: High current during WFE with nRF52832

Dmitry — Fri, 25 Oct 2019 15:05:51 GMT

WFE is able to stop/start internal HFCLK (HFINT) automatically. If you remove clocks_start() from your code, device will be clocked from HFINT, and it will stop at WFE, assuming you have no running peripheral that needs HFCLK.

External oscillator (HFXO) is started and stopped explicitly with TASKS_HFCLKSTART/TASKS_HFCLKSTOP, not by WFE.

RE: High current during WFE with nRF52832

eBrock — Fri, 25 Oct 2019 13:59:15 GMT

According to this table: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/pmu.html?cp=3_2_0_16_0_0_2#unique_498092668

I would assume that the WFE task is able to stop/start the HFCLK automatically, but in my testing, that isn't happening.

I don't see any errata for this issue. If there is a device problem, I'd like to know, so I can work on an alternative strategy for low-power mode.

RE: High current during WFE with nRF52832

eBrock — Fri, 25 Oct 2019 13:23:59 GMT

Perhaps a better question is: does the WFE task automatically stop the HFCLK?

RE: High current during WFE with nRF52832

Dmitry — Thu, 24 Oct 2019 20:43:29 GMT

I suggest you to read this chapter to better understand how clock controller works.

You need to start external HFCLK only when high-precision clocking is necessary - mainly for radio. It has longer startup time compared with internal clock and high power consumption during startup, so starting and stopping it on WFE is not a good idea. Internal oscillator is started and stopped automatically, and is suitable for most tasks that do not require precise timings.

RE: High current during WFE with nRF52832

eBrock — Thu, 24 Oct 2019 20:07:19 GMT

I assumed that the WFE task would handle clock switching automatically. Am I wrong?

If I start the LFCLK and stop the HFCLK before going to WFE, then current draw is about 3.5 uA.

Is this the correct way to use WFE task?

RE: High current during WFE with nRF52832

Dmitry — Thu, 24 Oct 2019 19:34:59 GMT

Hi,

in clocks_start() you're starting external oscillator (HFXO), according to documentation it consumes 250 uA. HFXO doesn't stop during WFE. Do you really need it for your test?