Change VDDH POF threshold when softdevice is enabled

[Florian Zierer]

I would like to measure the VDDH voltage (lithium ion battery) on a nrf52840 with the power fail comparator. If the voltage drops below the threshold, I want to reduce the threshold until I know the voltage.

The SDK says that an NRF_ERROR_INVALID_STATE is returned when the POF is initialized (with nrf_drv_power_pof_init) when SD is enabled.

Is there a way to change the threshold while a softdevice is running? Is there anything else I can do?

Of course I could measure the voltage as described in this thread, but I would like to reduce the amount of components on my board.

[run_ar]

When sd_power_pof_enable is enabled, the softdevice will notify the application with a NRF_EVT_POWER_FAILURE_WARNING event when the power failure occurs. The treshold can be adjusted with sd_power_pof_threshold_set. If you take a closer look at the POF documentation. You can see that When the supply voltage falls below the defined threshold, the power-fail comparator will generate an event (POFWARN) which can be used by an application to prepare for power failure. This event will also be generated if the supply voltage is already below the threshold at the time the power-fail comparator is enabled, or if the threshold is re-configured to a level above the supply voltage.

There is only one event generating the POF warning, so the Softdevice should generate the event as described in the nRF52840 OPS.

[Florian Zierer]

But why is in the nrf_drf_power_pof_init() the following comment

     /* Currently when SD is enabled - the configuration can be changed
     * in very limited range.
     * It is the SoftDevice limitation.
     */

#if NRF_POWER_HAS_VDDH
        if (p_config->thrvddh != nrf_power_pofcon_vddh_get())
        {
            /* Cannot change THRVDDH with current SD API */
            return NRF_ERROR_INVALID_STATE;
        }
#endif

I want to use it with the VDDH (it would be nrf_power_pofcon_vddh_set/get but it seems those equivalent functions are not yet implemented for the softdevice).

[run_ar]

Unfortunately it looks like you are right. I guess they haven't had time to add this for VDDH yet. Let me check internally if/when they plan on adding it.

[run_ar]

Looks like this is fixed already, meaning that I expect this to be working for VDDH in the next Softdevice release.

[Elkana]

Do you have update on this?

Is this updated in SDK 15.0.0?

[run_ar]

This should work with V6 softdevice, but I have not tested it to verify it. Use sd_power_pof_threshold_set. Please open a separate case if you have issues with this.