NRF7002-CEAA-R7 datasheet(12/69 Pages) NORDIC

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Power and clock management

• Retention RAMs: Active

• SPI/QSPI: On

5.2 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 SPI/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 is entered

opportunistically whenever there is no activity initiated from the host (for example, a scan request). In a

post-association condition, Sleep opportunities are determined by the negotiated Power Save mode of

the Access Point. No host interactions are required to enter Sleep, while the host invokes a transition from

Sleep to Active as part of any SPI/QSPI command transaction.

Transitioning from Shutdown or Sleep state to Active state involves the following steps:

1. Switch the Power Management Unit (PMU) to high power mode (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 initializations are required from Shutdown (including transferring the Factory

Information Configuration Registers (FICR) information from 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 channels to support scanning.

From Sleep, only minimal initialization or calibration on the operating channel is required.

See Electrical specification on page 34 for timing information.

5.3 Clock accuracy considerations

The crystal oscillator is active during normal operation, and is the clock reference for the RF synthesizer,

the Analog-to-Digital Converter (ADC)/Digital-to-Analog Converter (DAC) sample clocks, and the baseband

logic. The RTC is active during sleep state, and is used to run the wakeup timer used as part of Wi-Fi Power

Save. The crystal oscillator is inactive during sleep.

The IEEE 802.11 specification defines the accuracy of the Wi-Fi carrier frequency to be within ± 20 ppm

(in 5 GHz), which in turn defines the required accuracy of the external crystal. There is provision to trim

the crystal oscillator through a value programmed into the OTP memory on the nRF7002 device (or

any other available non-volatile memory). This trimming will compensate for the combined frequency

offset resulting from the crystal itself as well as any crystal oscillator variation at room temperature. The

crystal and crystal oscillator will both exhibit frequency drift across temperature, and the crystal will also

be subject to aging. The combination of these temperature and aging effects, along with the trimming

accuracy, will consume the majority of the ± 20 ppm allowance, assuming a crystal with ± 10 ppm stability

over temperature. The crystal tolerance (that is, accuracy at room temperature) is less important since this

4486_184 v1.2

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