74.10.1.1 Operation

Backup mode is designed to serve prolonged power-down periods of the processor. In this mode, only the backup area of the device powered by VBAT is maintained (RTC, GPBR, SHDWC, BSC_CR, SECUMOD). This mode is entered by shutting down all the power rails of the device except VBAT. It is good practice to use the SHDN output of the Shutdown Controller (SHDWC) for this purpose.

The device exits Backup mode when an active wake-up event is triggered by the SHDWC. Upon this wake-up event, the SHDWC automatically toggles its SHDN output back to VBAT and this signal typically helps to restart all the power supply channels at board level.

The wake-up events to exit Backup mode are:

• PIOBU[3:0]
• WKUP0 pin
• SECUMOD events
• RTT alarm
• RTC alarm