SWRU626 December 2025 CC3501E , CC3551E
The following power states and power state transitions are used in the device:
SHUTDOWN
The lowest power state of the device, SHUTDOWN is entered unconditionally when the reset pin is held low or the supply is below the minimum required. In this state no fast clocks are running, all voltage regulators are disabled and I/Os are in their default state. There is no internal mechanism to allow software to enter SHUTDOWN, nor any software mechanism to allow exit from SHUTDOWN.
SLEEP
SLEEP is the low power state of the device where slow clock is running and RTC and Watchdog timer can be active. The MCU domain is powered off, but all logic in the AON power domain remains on and clocked by slow clock. There are wake-up sources for SLEEP to ACTIVE as described in Section 5.4.3. On SLEEP exit, AAON is powered up again. MCU modules with retention will restore the state they had before SLEEP entry. See Figure 6-3 to see which modules have retention. Modules without retention are reset and need to be reconfigured when exiting SLEEP
IDLE
In IDLE the CPU is in sleep but selected peripherals and subsystems (such as the BLE-WiFi) can be active. In Idle mode, all modules are available and power consumption is highly application dependent.
ACTIVE
Once the reset pin is de-asserted and the minimum supply voltage is supplied, the device enters the ACTIVE power state. The fast clocks and internal LDOs are enabled. Once the digital supply and the internal slow clock (LFOSC) are stable, the cold boot sequence is performed, applying trims to analog circuitry (including oscillators and voltage regulators), memories and turn ON the fast clock of the device. The device boots, MCU is released from reset and start execution. The user application can configure and enable the LFXT or external slow clock. For more information on the boot process see Chapter 10. In the ACTIVE power state, both MCU and AON power domains are powered. Clock gating is used to minimize power consumption. Clock gating to peripherals/subsystems is controlled manually by the CPU.