NRF52811-QCAA-R datasheet(50/444 Pages) NORDIC

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Power and clock management

5.3.3 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.

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.

5.3.3.1 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 on page

50 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.

5.3.4 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 on page

51.

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NRF52811-QCAA-R Datasheet(PDF) 50 Page - Nordic Semiconductor