Power supply modes and regulators
nRF5340 supports two power supply voltage ranges, each with a dedicated power supply pin. The PMU automatically activates the correct voltage regulator depending on which power supply pin is used.
- Normal voltage mode - Powers the device through the VDD pin
- High voltage mode - Powers the device through the VDDH pin
In addition, the nRF5340 has a dedicated regulator used only for USB, controlled and operated separately using USBREG — USB regulator control.
The following figure shows the regulators and how they are connected to the supply pins.
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.
The VDD and VDDH pins are connected together. The external power supply is connected to the both pins. In this case, the VREGH regulator is automatically deactivated.
In normal voltage mode, each regulator can operate in LDO or DC/DC mode. See Normal voltage mode 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.
The external power supply is connected to the VDDH pin. The VREGMAIN and VREGRADIO regulators power the internal circuitry from the VDD pin. The VREGH regulator supplies the VDD pin.
By default, the high voltage regulator is configured to source external components from the VDD pin. To save power this feature must be disabled. For details, see High voltage mode.
In high voltage mode, each of the three regulators can operate in LDO or DC/DC mode. See High voltage mode for details about configuring the regulators in this mode.
Power supply supervisor
Several voltage monitoring devices, enabled through the power management unit (PMU), monitor the connected power supply.
The following figure illustrates the main components for power supply supervision.
The power supply mode detector determines which supply pin is used when the device is powered up. It selects the appropriate power supply mode, generates the enable signal that automatically enables VREGH, and generates a power-on reset (POR) initializing the device. For an overview of the supply modes, see Power supply modes and regulators.
The brownout detector monitors the VDD supply (input of the VREGMAIN regulator) to ensure safe operation. It generates a brownout reset (BOR) when 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.
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 give the CPU time to prepare for an orderly power-down. The following figure shows the main elements of the POF.
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 generates the event POFWARN that is sent to the POWER module within both the application and network cores. Software running on both cores uses this signal to prepare for a power failure. This event is also generated when the supply voltage is 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 prevents the NVMC from performing write operations to the NVM.
To save power, the power-fail comparator is not active in System OFF or in System ON when HFCLK is not running.
The POF features a hysteresis of VPOFHYST, as illustrated in the following figure.
The POF hysteresis voltage is defined with the VPOFHYST parameter in Electrical specification.