Power supply monitoring

Power supply supervisor

The power supply supervisor enables monitoring of the connected power supply.

Two functionalities are implemented:

Power-on reset (POR): Generates a reset when the supply is applied to the device, and ensures that the device starts up in a known state
Brownout reset (BOR): Generates a reset when the supply drops below the minimum voltage required for safe operations

Two BOR levels are used:

V_BOROFF, used in System OFF
V_BORON, used in System ON

The power supply supervisor is illustrated in the image below.

Figure 1. Power supply supervisor

External power failure warning

The external power failure (EXTPOF) warning can provide the CPU an early warning of an imminent power failure. It will not reset the system, but give the CPU time to prepare for an orderly power-down. EXTPOF detects power failures external to PMU from the device internal PMIC.

Note: This feature is only supported with nRF9160 modem firmware version 1.3.1 and higher.

The user can start and stop the PMIC EXTPOF feature and set the battery voltage low threshold level through the modem API.

To receive the power failure warning events on application core the user must also enable the EXTPOFCON register in REGULATORS — Voltage regulators control. If this is disabled, the state of the PMIC warning input is ignored and the power failure warning events are not delivered to application core.

The available time for the CPU to prepare for a power-down depends on the set warning threshold level, the load of the running tasks, and the type of power source used.

Note: For details on services provided by the modem AT command interface, see nRF Connect SDK AT interface and nRF91 AT Commands.

The EXTPOF arrangement is illustrated in the following image.

Figure 2. External power failure warning arrangement

If EXTPOF is enabled and the device internal PMIC detects battery voltage dropping below the programmed low threshold level, the POFWARN event is generated (see EVENTS_POFWARN). The POFWARN event to CPU can be cleared in this event register, however the PMIC input continues to indicate warning as long as the battery voltage stays below the low threshold level.

POFWARN event also sets the LTE modem in offline mode.

Note: If power failure warning occurs during an ongoing NVM write operation, the NVMC will try to finish the operation. Consecutive NVM write operations will be blocked by the NVMC as long as the PMIC input indicates warning. The CPU will see a blocked NVM write as a fault, which needs to be handled in the software. If power failure warning occurs during an ongoing NVM erase operation, the operation will be aborted. Blocking NVM writes and aborting NVM erase operations can be disabled in APPNVMCPOFGUARD.

The external power failure warning doesn't trigger wakeup from System OFF.

The external power failure warning is disabled in System OFF mode.

Battery monitoring on VDD

A battery voltage (VDD) monitoring capability is provided via a modem API.

Note: For details on services provided by the modem AT command interface, see nRF Connect SDK AT interface and nRF91 AT Commands.

Registers

Electrical specification

Device startup times

Symbol	Description	Min.	Typ.	Max.	Units
t_POR	Time in power-on reset after VDD has reached 3V, ENABLE is tied to VDD.		1.2		ms
t_PINR	The maximum time taken to pull up the nRESET pin and release reset after power-on reset. Dependent on the pin capacitive load (C)¹: t=TRC; Typical: T=2 R=13 kΩ; Max: T=5 R=16 kΩ.	..	..	..
t_PINR,500nF	C=500 nF		13	40	ms
t_PINR,10uF	C=10 µF		260	800	ms
t_R2ON	Time from reset to ON (CPU execute)		127	135	µs
t_OFF2ON	Time from OFF to CPU execute		73	92	µs
t_WFE2CPU	Time from WFE to CPU execute		70	90	µs
t_WFI2CPU	Time from WFI to CPU execute		69	90	µs
t_EVTSET,CL1	Time from HW event to PPI event in constant latency System ON mode		0.1	0.1	µs
t_EVTSET,CL0	Time from HW event to PPI event in low power System ON mode		0.1	0.7	µs
t_LTEMODEM,TYP	LTE modem typical startup time. Time from application core powering up the modem until the modem is ready to receive the first AT command.			200	ms
t_{LTEMODEM,WORSTCASE}	LTE modem worst case startup time. Time from application core powering up the modem until the modem is ready to receive the first AT command, with modem FW variable elements included.			250	ms
t_{LTEMODEM,FOTA}	LTE modem startup time after modem FOTA update. Time from application core powering up the modem after a modem FOTA update until the modem is ready to receive the first AT command.			7.5	s
t_{LTEMODEM,FOTAREJECT}	LTE modem startup time after a rejected modem FOTA update. Time from application core powering up the modem after a rejected modem FOTA update until the modem is ready to receive the first AT command. Modem will revert back to original FW image.			90	s
t_{LTEMODEM,STOP,TYP}	LTE modem typical shutdown time. Time from application core calling bsd_shutdown command until bsd_shutdown returns.			1.6	s
t_{LTEMODEM,STOP,WORSTCASE}	LTE modem worst case shutdown time. Time from application core calling bsd_shutdown command until bsd_shutdown returns, with modem FW variable elements included.			79	s

Power supply supervisor

Symbol	Description				Min.	Typ.	Max.	Units
V_BOR	Brownout reset voltage threshold.					2.00		V
V_POR	Voltage threshold at which the device enters power-on reset (POR) when VDD is ramping up.						2.15	V