What is the current consumption below minimum voltage.

[Andrew Lohmann]

Nordic nRF52832 chipset Battery operation such as CR2477 Lithium Manganese primary button cell.

Many application circuits show this microcontroller used with a button cell. Such as BL652 made by Laird. We planning to use this module but I am advised by Duracell that the battery may leak if it is over discharged. So my plan is to periodically measure the supply voltage and if it is below 1.9V, say, switch the microcontroller to its lowest power mode. Periodically retesting the battery voltage so that the device will return to normal operation if the battery is replaced.

My concern is to guess what the Nordic chip will do as the voltage drops eg will it go into a reset mode and then draw more current?

Alternatively if I include a low voltage reset generator circuit would holding the Nordic chip in reset cause increased current?

[Sigurd]

Hi,

Most of these lithium coin cell batteries have almost no risk of leaking, so leakage is not normally a concern when using a lithium coin cell. (Alkaline batteries on the other hand are prone to leaking)

So my plan is to periodically measure the supply voltage and if it is below 1.9V, say, switch the microcontroller to its lowest power mode.

With the nRF52832 we have Power-fail comparator you can use for this. The power-fail comparator (POF) can provide the CPU with an early warning of impending power failure. It will not reset the system, but give the CPU time to prepare for an orderly power-down.

With the SoftDevice enabled, you can use the function sd_power_pof_threshold_set() to set the power-fail threshold value and sd_power_pof_enable() to enable the power-fail comparator. Use NRF_POWER_THRESHOLD_V19 to set a 1.9 Volts power failure threshold.

You will get the event NRF_EVT_POWER_FAILURE_WARNING when the power failure warning occur. You can then orderly uninitialize you system as you want, and then put the chip in System OFF mode. System OFF is the deepest power saving mode the system can enter. In this mode, the system’s core functionality is powered down and all ongoing tasks are terminated, and the current consumption is only 0.3 µA.

[Andrew Lohmann]

Thank you Sigurd,

There are many features that are not available to us through SmartBASIC that we are using at present. So I doubt that we will be able to take advantage of the features you mention in the short term.

For example our software team can not access watchdog so I have an external watchdog and reset generator. That will hold the reset pin low when the input voltage is low and that is why I asked about current consumption in that situation.

Lastly on the Lithium Manganese button cell thank you for advising me that the risk of leakage is low which means I do not necessarily need to worry about that warning Duracell advised me of.