Power supply modes and regulators

nRF5340 supports two different power supply voltage ranges, each having a corresponding power supply pin. The PMU automatically activates the correct voltage regulator depending on which power supply pin is used.

The nRF5340 PMU controls three different regulators to support the following power supply modes:

The three regulators and how they are connected to the supply pins are shown in the following figure.

Figure 1. Regulators used in nRF5340
Three regulators in use: VREGH, VREGMAIN, and VREGRADIO

Normal voltage mode

When the device operates in normal voltage mode, only the main voltage regulator (VREGMAIN) and the radio voltage regulator (VREGRADIO) are used.

Figure 2. Regulator usage in Normal voltage mode
Regulator usage in Normal voltage mode

The external power supply is connected to the VDD pin. The VDDH pin is connected to VDD, but the VREGH regulator is deactivated.

In normal voltage mode, each regulator can operate in LDO or DC/DC mode. See Normal voltage mode - detailed setup for details about configuration of the regulators in this mode.

High voltage mode

When the device operates in high voltage mode, the high voltage regulator (VREGH), the main voltage regulator (VREGMAIN) and the radio voltage regulator (VREGRADIO) are used.

Figure 3. Regulator usage in High voltage mode
Regulator usage in High voltage mode

The external power supply is connected to the VDDH pin. The VREGMAIN and VREGRADIO regulators are used to power the internal circuitry from the VDD pin. The VDD pin is supplied by the VREGH regulator.

In high voltage mode, each of the three regulators can operate in LDO or DC/DC mode. See High voltage mode - detailed setup for details about configuring the regulators in this mode.

Power supply supervisor

Several voltage monitoring devices, enabled through the power management unit (PMU), are used to monitor the connected power supply.

The following figure illustrates the main components for power supply supervision.

Figure 4. Power supply supervision in nRF5340

The power supply mode detector determines which supply pin is used when the device is powered up. It selects the power supply mode accordingly, and generates a power-on reset (POR) which initializes the device. For an overview of the different supply modes, see Power supply modes and regulators.

The brownout detector monitors the VDD supply (input of the VREGMAIN regulator) to ensure safe operation, and generates a brownout reset (BOR) if the voltage is too low, holding the device in reset when the voltage is too low for safe operation. The brownout reset voltage is defined in parameters VBOR,OFF and VBOR,ON.

The optional power-fail comparator (POF) can be used to signal the application when the supply voltage drops below a configured threshold. For details on the POF, see Power-fail comparator.

Power-fail comparator

The power-fail comparator (POF) can provide the CPU with an early warning of an impending power supply failure.

The POF can be used to signal the application when the supply voltage drops below a configured threshold. The POF will not reset the system, but instead give the CPU time to prepare for an orderly power-down. The following figure shows the main elements of the POF.

Figure 5. Power-fail comparator
Power-fail comparator

Using the POF is optional, and must be enabled and configured through the register POFCON ( Retained ).

Depending on the supply mode (see Power supply modes and regulators), the thresholds VPOF and VPOFH must be configured to a suitable level through the POFCON register. When the supply voltage falls below the defined threshold, the POF will generate the event POFWARN that is sent to the POWER module within both the application and network cores. Software running on the two cores can use this signal to prepare for a power failure. This event is also generated when the supply voltage is already below the threshold at the time the power-fail comparator is enabled, or if the threshold is reconfigured to a level above the supply voltage.

If the POF is enabled and the supply voltage is below the threshold, the POF will prevent the NVMC from performing write operations to the NVM.

To save power, the POF is not active in System OFF.

The POF features a hysteresis of VPOFHYST, as illustrated in the following figure.

Figure 6. POF hysteresis and POFWARN event (BOR = brownout reset)
POF hysteresis and POFWARN event (BOR = brownout reset)

The POF hysteresis voltage is defined with the VPOFHYST parameter in Electrical specification.


This document was last updated on
2019-12-09.
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