Power state operation

Apart from transitions in or out of Shutdown state through the BUCKEN pin, all transitions between Sleep and Active states are automatic and do not rely on any control pin assertion or de-assertion.

Shutdown state is achieved by de-assertion on the BUCKEN pin. Asserting BUCKEN will result in the Active (IDLE sub-state) state being entered. The host will initiate the boot sequence through Serial Peripheral Interface (SPI)/Quad Serial Peripheral Interface (QSPI), culminating in the Sleep state being entered. This is the lowest power non-Shutdown state that can be achieved. Transitions from Active to Sleep are fully controlled by nRF7002. Transitions from Sleep to Active are determined by both the host and nRF7002. In a pre-association condition, Sleep will be entered opportunistically whenever there is no activity initiated from the host (for example, a scan request). In a post-association condition, Sleep opportunities will be determined by the negotiated Power Save mode of the Access Point. No host interactions are required to enter Sleep, while the host will invoke a transition from Sleep to Active as part of any SPI/QSPI command transaction.

The steps used to transition from Shutdown or Sleep into Active are as follows:

1. Switch the Power Management Unit (PMU) to high power mode (Pulse-Width Modulation (PWM)).
2. Apply power to the digital logic, RAMs, and analog circuits.
3. Start the 40 MHz crystal oscillator and allow to settle.
4. Start the baseband PLL and allow to settle.
5. Boot all processor cores.
6. Execute baseband initializations.
7. Execute RF initializations and calibrations.

The initial steps consume equal duration whether originating in Shutdown or Sleep, while the baseband and RF initializations are dependent on the originating state. In particular:

• Full baseband initialisations are required from Shutdown (including transferring the Factory Information Configuration Registers (FICR) information from One Time Programmable (OTP) memory into retention RAM), while in Sleep some of the state is retained in retention RAMs.
• Complete RF calibrations are required from Shutdown, including across bands/channels in order to support scanning. From Sleep, only minimal initialization or calibration on the operating channel is required.

See Electrical specification for timing information.