POWER — Power supply

This device has the following power supply features:

  • On-chip LDO and DC/DC regulators
  • Global System ON/OFF modes with individual RAM section power control
  • Analog or digital pin wakeup from System OFF
  • Supervisor HW to manage power on reset, brownout, and power fail
  • Auto-controlled refresh modes for LDO and DC/DC regulators to maximize efficiency
  • Automatic switching between LDO and DC/DC regulator based on load to maximize efficiency
Note: Two additional external passive components are required to use the DC/DC regulator.

Regulators

The following internal power regulator alternatives are supported:
  • Internal LDO regulator
  • Internal DC/DC regulator

The LDO is the default regulator.

The DC/DC regulator can be used as an alternative to the LDO regulator and is enabled through the DCDCEN register. Using the DC/DC regulator will reduce current consumption compared to when using the LDO regulator, but the DC/DC regulator requires an external LC filter to be connected, as shown in DC/DC regulator setup.

Figure 1. LDO regulator setup

Figure 2. DC/DC regulator setup

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.

The device can be put into System OFF mode using the register SYSTEMOFF. When in System OFF mode, the device can be woken up through one of the following signals:

  • The DETECT signal, optionally generated by the GPIO peripheral
  • A reset

When the system wakes up from System OFF mode, it gets reset. For more details, see Reset behavior.

One or more RAM sections can be retained in System OFF mode, depending on the settings in the RAM[n].POWER registers.

RAM[n].POWER are retained registers, see Reset behavior. These registers are usually overwritten by the startup code provided with the nRF application examples.

Before entering System OFF mode, the user must make sure that all on-going EasyDMA transactions have been completed. This is usually accomplished by making sure that the EasyDMA enabled peripheral is not active when entering System OFF.

Emulated System OFF mode

If the device is in debug interface mode, System OFF will be emulated to secure that all required resources needed for debugging are available during System OFF.

See Debug for more information. Required resources needed for debugging include the following key components:Since the CPU is kept on in an emulated System OFF mode, it is recommended to add an infinite loop directly after entering System OFF, to prevent the CPU from executing code that normally should not be executed.

System ON mode

System ON is the default state after power-on reset. In System ON, all functional blocks such as the CPU or peripherals can be in IDLE or RUN mode, depending on the configuration set by the software and the state of the application executing.

Register RESETREAS provides information about the source causing the wakeup or reset.

The system can switch the appropriate internal power sources on and off, depending on how much power is needed at any given time. The power requirement of a peripheral is directly related to its activity level, and the activity level of a peripheral is usually raised and lowered when specific tasks are triggered or events are generated.

Sub power modes

In System ON mode, when both the CPU and all the peripherals are in IDLE mode, the system can reside in one of the two sub power modes.

The sub power modes are:

  • Constant Latency
  • Low-power

In Constant Latency mode, the CPU wakeup latency and the PPI task response are constant and kept at a minimum. This is secured by forcing a set of basic resources to be turned on while in sleep. Having a constant and predictable latency is at the cost of having increased power consumption. The Constant Latency mode is selected by triggering the CONSTLAT task.

In Low-power mode, the automatic power management system described in System ON mode ensures that the most efficient supply option is chosen to save most power. Having the lowest power possible is at the cost of having a varying CPU wakeup latency and PPI task response. The Low-power mode is selected by triggering the LOWPWR task.

When the system enters System ON mode, it is by default in Low-power sub power mode.

Power supply supervisor

The power supply supervisor initializes the system at power-on and provides an early warning of impending power failure.

In addition, the power supply supervisor puts the system in a reset state if the supply voltage is too low for safe operation (brownout). The power supply supervisor is illustrated in Power supply supervisor.

Figure 3. Power supply supervisor

Power-fail comparator

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.

The comparator features a hysteresis of VHYST, as illustrated in Power-fail comparator (BOR = Brownout reset). The threshold VPOF is set in register POFCON. If the POF is enabled and the supply voltage falls below VPOF, the POFWARN event will be generated. This event will also be generated if the supply voltage is already below VPOF at the time the POF is enabled, or if VPOF is re-configured to a level above the supply voltage.

If power-fail warning is enabled and the supply voltage is below VPOF the power-fail comparator will prevent the NVMC from performing write operations to the NVM. See NVMC — Non-volatile memory controller for more information about the NVMC.

Figure 4. Power-fail comparator (BOR = Brownout reset)

To save power, the power-fail comparator is not active in System OFF or in System ON when HFCLK is not running.

RAM power control

The RAM power control registers are used for configuring the following:

  • The RAM sections to be retained during System OFF
  • The RAM sections to be retained and accessible during System ON

In System OFF, retention of a RAM section is configured in the RETENTION field of the corresponding RAM[n] register.

In System ON, retention and accessibility for a RAM section is configured in the RETENTION and POWER fields of the corresponding RAM[n] register.

The following table summarizes the behavior of these registers.

Table 1. RAM section configuration
Configuration  RAM section status 
System on/offRAM[n].POWER.POWERRAM[n].POWER.RETENTIONAccessibleRetained
OffxOffNoNo
OffxOnNoYes
OnOffOffNoNo
OnOff1OnNoYes
OnOnxYesYes

The advantage of not retaining RAM contents is that the overall current consumption is reduced.

See chapter Memory for more information on RAM sections.

Reset

There are multiple sources that may trigger a reset.

After a reset has occurred, register RESETREAS can be read to determine which source generated the reset.

Power-on reset

The power-on reset generator initializes the system at power-on.

The system is held in reset state until the supply has reached the minimum operating voltage and the internal voltage regulators have started.

A step increase in supply voltage of 300 mV or more, with rise time of 300 ms or less, within the valid supply range, may result in a system reset.

Pin reset

A pin reset is generated when the physical reset pin on the device is asserted.

Pin reset is configured via the PSELRESET[n] registers.

Note: Pin reset is not available on all pins.

Wakeup from System OFF mode reset

The device is reset when it wakes up from System OFF mode.

The debug access port (DAP) is not reset following a wake up from System OFF mode if the device is in Debug Interface mode. See chapter Debug for more information.

Soft reset

A soft reset is generated when the SYSRESETREQ bit of the Application Interrupt and Reset Control Register (AIRCR register) in the ARM® core is set.

Refer to ARM documentation for more details.

A soft reset can also be generated via the RESET register in the CTRL-AP.

Watchdog reset

A Watchdog reset is generated when the watchdog times out.

See chapter WDT — Watchdog timer for more information.

Brown-out reset

The brown-out reset generator puts the system in reset state if the supply voltage drops below the brownout reset (BOR) threshold.

Refer to section Power fail comparator for more information.

Retained registers

A retained register is a register that will retain its value in System OFF mode and through a reset, depending on reset source. See individual peripheral chapters for information of which registers are retained for the various peripherals.

Reset behavior

Reset sourceReset target
CPUPeripheralsGPIODebugaSWJ-DPRAMWDTRetained registersRESETREAS
CPU lockup 3xxx      
Soft resetxxx      
Wakeup from System OFF mode resetxx x 4 x 5x  
Watchdog reset 6xxxx xxx 
Pin resetxxxx xxx 
Brownout resetxxxxxxxxx
Power on resetxxxxxxxxx
Note: The RAM is never reset, but depending on reset source, RAM content may be corrupted.

Registers

Table 2. Instances
Base addressPeripheralInstanceDescriptionConfiguration
0x40000000POWERPOWER

Power control

For 24 kB RAM variant, only RAM[0].x to RAM[2].x registers are in use.

 
Table 3. Register overview
RegisterOffsetDescription
TASKS_CONSTLAT0x078

Enable Constant Latency mode

 
TASKS_LOWPWR0x07C

Enable Low-power mode (variable latency)

 
EVENTS_POFWARN0x108

Power failure warning

 
EVENTS_SLEEPENTER0x114

CPU entered WFI/WFE sleep

 
EVENTS_SLEEPEXIT0x118

CPU exited WFI/WFE sleep

 
INTENSET0x304

Enable interrupt

 
INTENCLR0x308

Disable interrupt

 
RESETREAS0x400

Reset reason

 
SYSTEMOFF0x500

System OFF register

 
POFCON0x510

Power failure comparator configuration

 
GPREGRET0x51C

General purpose retention register

 
GPREGRET20x520

General purpose retention register

 
DCDCEN0x578

DC/DC enable register

 
RAM[0].POWER0x900

RAM0 power control register. The RAM size will vary depending on product variant, and the RAM0 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[0].POWERSET0x904

RAM0 power control set register

 
RAM[0].POWERCLR0x908

RAM0 power control clear register

 
RAM[1].POWER0x910

RAM1 power control register. The RAM size will vary depending on product variant, and the RAM1 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[1].POWERSET0x914

RAM1 power control set register

 
RAM[1].POWERCLR0x918

RAM1 power control clear register

 
RAM[2].POWER0x920

RAM2 power control register. The RAM size will vary depending on product variant, and the RAM2 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[2].POWERSET0x924

RAM2 power control set register

 
RAM[2].POWERCLR0x928

RAM2 power control clear register

 
RAM[3].POWER0x930

RAM3 power control register. The RAM size will vary depending on product variant, and the RAM3 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[3].POWERSET0x934

RAM3 power control set register

 
RAM[3].POWERCLR0x938

RAM3 power control clear register

 
RAM[4].POWER0x940

RAM4 power control register. The RAM size will vary depending on product variant, and the RAM4 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[4].POWERSET0x944

RAM4 power control set register

 
RAM[4].POWERCLR0x948

RAM4 power control clear register

 
RAM[5].POWER0x950

RAM5 power control register. The RAM size will vary depending on product variant, and the RAM5 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[5].POWERSET0x954

RAM5 power control set register

 
RAM[5].POWERCLR0x958

RAM5 power control clear register

 
RAM[6].POWER0x960

RAM6 power control register. The RAM size will vary depending on product variant, and the RAM6 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[6].POWERSET0x964

RAM6 power control set register

 
RAM[6].POWERCLR0x968

RAM6 power control clear register

 
RAM[7].POWER0x970

RAM7 power control register. The RAM size will vary depending on product variant, and the RAM7 register will only be present if the corresponding RAM AHB slave is present on the device.

 
RAM[7].POWERSET0x974

RAM7 power control set register

 
RAM[7].POWERCLR0x978

RAM7 power control clear register

 

TASKS_CONSTLAT

Address offset: 0x078

Enable Constant Latency mode

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
AW

TASKS_CONSTLAT

  

Enable Constant Latency mode

   

Trigger

1

Trigger task

TASKS_LOWPWR

Address offset: 0x07C

Enable Low-power mode (variable latency)

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
AW

TASKS_LOWPWR

  

Enable Low-power mode (variable latency)

   

Trigger

1

Trigger task

EVENTS_POFWARN

Address offset: 0x108

Power failure warning

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

EVENTS_POFWARN

  

Power failure warning

   

NotGenerated

0

Event not generated

   

Generated

1

Event generated

EVENTS_SLEEPENTER

Address offset: 0x114

CPU entered WFI/WFE sleep

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

EVENTS_SLEEPENTER

  

CPU entered WFI/WFE sleep

   

NotGenerated

0

Event not generated

   

Generated

1

Event generated

EVENTS_SLEEPEXIT

Address offset: 0x118

CPU exited WFI/WFE sleep

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

EVENTS_SLEEPEXIT

  

CPU exited WFI/WFE sleep

   

NotGenerated

0

Event not generated

   

Generated

1

Event generated

INTENSET

Address offset: 0x304

Enable interrupt

Bit number313029282726252423222120191817161514131211109876543210
ID                         

C

B

  

A

  
Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

POFWARN

  

Write '1' to enable interrupt for event POFWARN

   

Set

1

Enable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

BRW

SLEEPENTER

  

Write '1' to enable interrupt for event SLEEPENTER

   

Set

1

Enable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

CRW

SLEEPEXIT

  

Write '1' to enable interrupt for event SLEEPEXIT

   

Set

1

Enable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number313029282726252423222120191817161514131211109876543210
ID                         

C

B

  

A

  
Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

POFWARN

  

Write '1' to disable interrupt for event POFWARN

   

Clear

1

Disable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

BRW

SLEEPENTER

  

Write '1' to disable interrupt for event SLEEPENTER

   

Clear

1

Disable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

CRW

SLEEPEXIT

  

Write '1' to disable interrupt for event SLEEPEXIT

   

Clear

1

Disable

   

Disabled

0

Read: Disabled

   

Enabled

1

Read: Enabled

RESETREAS

Address offset: 0x400

Reset reason

Unless cleared, the RESETREAS register will be cumulative. A field is cleared by writing '1' to it. If none of the reset sources are flagged, this indicates that the chip was reset from the on-chip reset generator, which will indicate a power-on-reset or a brownout reset.

Bit number313029282726252423222120191817161514131211109876543210
ID            

F

 

E

            

D

C

B

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

RESETPIN

  

Reset from pin-reset detected

   

NotDetected

0

Not detected

   

Detected

1

Detected

BRW

DOG

  

Reset from watchdog detected

   

NotDetected

0

Not detected

   

Detected

1

Detected

CRW

SREQ

  

Reset from soft reset detected

   

NotDetected

0

Not detected

   

Detected

1

Detected

DRW

LOCKUP

  

Reset from CPU lock-up detected

   

NotDetected

0

Not detected

   

Detected

1

Detected

ERW

OFF

  

Reset due to wake up from System OFF mode when wakeup is triggered from DETECT signal from GPIO

   

NotDetected

0

Not detected

   

Detected

1

Detected

FRW

DIF

  

Reset due to wake up from System OFF mode when wakeup is triggered from entering into debug interface mode

   

NotDetected

0

Not detected

   

Detected

1

Detected

SYSTEMOFF

Address offset: 0x500

System OFF register

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
AW

SYSTEMOFF

  

Enable System OFF mode

   

Enter

1

Enable System OFF mode

POFCON

Address offset: 0x510

Power failure comparator configuration

Bit number313029282726252423222120191817161514131211109876543210
ID                          

B

B

B

B

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

POF

  

Enable or disable power failure comparator

   

Disabled

0

Disable

   

Enabled

1

Enable

BRW

THRESHOLD

  

Power failure comparator threshold setting

   

V17

4

Set threshold to 1.7 V

   

V18

5

Set threshold to 1.8 V

   

V19

6

Set threshold to 1.9 V

   

V20

7

Set threshold to 2.0 V

   

V21

8

Set threshold to 2.1 V

   

V22

9

Set threshold to 2.2 V

   

V23

10

Set threshold to 2.3 V

   

V24

11

Set threshold to 2.4 V

   

V25

12

Set threshold to 2.5 V

   

V26

13

Set threshold to 2.6 V

   

V27

14

Set threshold to 2.7 V

   

V28

15

Set threshold to 2.8 V

GPREGRET

Address offset: 0x51C

General purpose retention register

Bit number313029282726252423222120191817161514131211109876543210
ID                        

A

A

A

A

A

A

A

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

GPREGRET

  

General purpose retention register

This register is a retained register

GPREGRET2

Address offset: 0x520

General purpose retention register

Bit number313029282726252423222120191817161514131211109876543210
ID                        

A

A

A

A

A

A

A

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

GPREGRET

  

General purpose retention register

This register is a retained register

DCDCEN

Address offset: 0x578

DC/DC enable register

Bit number313029282726252423222120191817161514131211109876543210
ID                               

A

Reset 0x0000000000000000000000000000000000000000
IDAccessFieldValue IDValueDescription
ARW

DCDCEN

  

Enable or disable DC/DC converter

   

Disabled

0

Disable

   

Enabled

1

Enable

RAM[n].POWER (n=0..7)

Address offset: 0x900 + (n × 0x10)

RAMn power control register. The RAM size will vary depending on product variant, and the RAMn register will only be present if the corresponding RAM AHB slave is present on the device.

Bit number313029282726252423222120191817161514131211109876543210
ID              

D

C

              

B

A

Reset 0x0000FFFF00000000000000001111111111111111
IDAccessFieldValue IDValueDescription
A-BRW

S[i]POWER (i=0..1)

  

Keep RAM section Si ON or OFF in System ON mode.

RAM sections are always retained when ON, but can also be retained when OFF dependent on the settings in SiRETENTION. All RAM sections will be OFF in System OFF mode.

   

Off

0

Off

   

On

1

On

C-DRW

S[i]RETENTION (i=0..1)

  

Keep retention on RAM section Si when RAM section is in OFF

   

Off

0

Off

   

On

1

On

RAM[n].POWERSET (n=0..7)

Address offset: 0x904 + (n × 0x10)

RAMn power control set register

When read, this register will return the value of the POWER register.

Bit number313029282726252423222120191817161514131211109876543210
ID              

D

C

              

B

A

Reset 0x0000FFFF00000000000000001111111111111111
IDAccessFieldValue IDValueDescription
A-BW

S[i]POWER (i=0..1)

  

Keep RAM section Si of RAMn on or off in System ON mode

   

On

1

On

C-DW

S[i]RETENTION (i=0..1)

  

Keep retention on RAM section Si when RAM section is switched off

   

On

1

On

RAM[n].POWERCLR (n=0..7)

Address offset: 0x908 + (n × 0x10)

RAMn power control clear register

When read, this register will return the value of the POWER register.

Bit number313029282726252423222120191817161514131211109876543210
ID              

D

C

              

B

A

Reset 0x0000FFFF00000000000000001111111111111111
IDAccessFieldValue IDValueDescription
A-BW

S[i]POWER (i=0..1)

  

Keep RAM section Si of RAMn on or off in System ON mode

   

Off

1

Off

C-DW

S[i]RETENTION (i=0..1)

  

Keep retention on RAM section Si when RAM section is switched off

   

Off

1

Off

Electrical specification

Device startup times

SymbolDescriptionMin.Typ.Max.Units
tPOR

Time in Power on Reset after VDD reaches 1.7 V for all supply voltages and temperatures. Dependent on supply rise time. 7

 
tPOR,10us

VDD rise time 10 µs

1ms
tPOR,10ms

VDD rise time 10 ms

9ms
tPOR,60ms

VDD rise time 60 ms

23ms
tPINR

If a GPIO pin is configured as reset, the maximum time taken to pull up the pin and release reset after power on reset. Dependent on the pin capacitive load (C)8: t=5RC, R = 13 kΩ

 
tPINR,500nF

C = 500 nF

32.5ms
tPINR,10uF

C = 10 µF

650ms
tR2ON

Time from reset to ON (CPU execute)

 
tR2ON,NOTCONF

If reset pin not configured

tPORms
tR2ON,CONF

If reset pin configured

tPOR + tPINRms
tOFF2ON

Time from OFF to CPU execute

16.5µs
tIDLE2CPU

Time from IDLE to CPU execute

3.0µs
tEVTSET,CL1

Time from HW event to PPI event in Constant Latency System ON mode

0.0625µs
tEVTSET,CL0

Time from HW event to PPI event in Low Power System ON mode

0.0625µs

Power fail comparator

SymbolDescriptionMin.Typ.Max.Units
VPOF

Nominal power level warning thresholds (falling supply voltage). Levels are configurable between Min. and Max. in 100 mV increments.

1.72.8V
VPOFTOL

Threshold voltage tolerance

±1±5%
VPOFHYST

Threshold voltage hysteresis

50mV
VBOR,OFF

Brown out reset voltage range SYSTEM OFF mode

1.21.7V
VBOR,ON

Brown out reset voltage range SYSTEM ON mode

1.481.7V
1 Not useful setting. RAM section power off gives negligible reduction in current consumption when retention is on.
a All debug components excluding SWJ-DP. See Debug for more information about the different debug components in the system.
3 Reset from CPU lockup is disabled if the device is in debug interface mode. CPU lockup is not possible in System OFF.
4 The Debug components will not be reset if the device is in debug interface mode.
5 RAM is not reset on wakeup from System OFF mode, but depending on settings in the RAM registers, parts, or the whole RAM may not be retained after the device has entered System OFF mode.
6 Watchdog reset is not available in System OFF.
7 A step increase in supply voltage of 300 mV or more, with rise time of 300 ms or less, within the valid supply range, may result in a system reset.
8 To decrease maximum time a device could hold in reset, a strong external pullup resistor can be used.