Power-fail comparator

[Nikita]

I have a few questions regarding power-fail comparator (POF).

1. How much current POF consumes? About the same as low power comparator (0.5uA) or lower?
2. How will softdevice manage POF? If I enable POF with sd_power_pof_enable() will POF be enabled the whole time or be enabled when CPU is running and disabling when I'll go to the low power mode with sd_app_evt_wait()? Or should I disable it myself before entering low power mode and enabling it after returning from low power mode? This question affects current consumption and also this text from reference manual:

The power failure comparator is only intended to be used as long as the CPU is running. If the power failure comparator is enabled when the CPU is not running, this may result in unpredictable behavior in the power failure comparator.

To joc:

This text was in old nRF51 series reference manual v2.1.

[Stefan Birnir Sverrisson]

Hi Nikita

I had been using the POF some time ago in System On low power mode (initiated with sd_app_evt_wait, __WFI or __WFE), with and without softdevice, without any complications. However, from the text that you mention from the reference manual, the POF is enabled only when the 1v2 regulator is enabled. When in System On low power mode or System Off mode, the 1v2 regulator is not enabled, unless you explicitly enable the "Constant latency" mode

The POF consumes around 10uA when enabled. For a typical BLE application where the CPU generally is awake for a short period and then sleeps for a long period, the current consumption should be <1uA.

Update 24.8.2015 The mentioned statement in the nrF51 Series Reference Manual v2.1 (for nRF51 second revision), about not operating the POF unless the CPU is running, was not accurate and was removed from the nRF51 Series Reference Manual v3.0 (for nRF51 third revision). The functionality of the POF remained however identical for nRF51 second and third revision.

If the POF is enabled, then it will be operational and give a warning if there are any other peripherals on the chip enabled (which makes the 1v2 regulator enabled, which the POF requires). If the 1v2 regulator is disabled (typically when the nRF51 is in System On low power mode or System Off), then the POF is disabled and will not give low power warning. When the 1v2 regulator becomes available again, the POF will again be active and give low power warning if low voltage threshold is reached.

[joc]

Is that to say we no longer need disable POF before app event wait, only need setup at initial time for 3rd version chip per the series reference manual version 3.0?