74.5.2 Backup Mode Entry and Wake-up

The following figure shows the recommended power-down sequence to place the device in Backup mode. The SHDN signal, output of the Shutdown Controller (SHDWC), signals the shutdown request to the external power supply. This output is supplied by VBAT present in Backup mode. In a similar way to the power-down sequence, the NRST signal must be asserted prior to turning the device power supplies off.

Figure 74-4. Recommended Power Sequence at Backup Mode Entry

Table 74-12. Backup Mode Entry Timing Requirements
Symbol	Parameter	Conditions	Min	Max	Unit
t_SHDN	SHDN delay at backup mode entry	Delay from SHDN low to NRST low	0	–	ms
t_RSTPD	NRST delay at power-down	Delay from NRST low to the first supply out of its operating range	0	–	ms

The following figure shows the recommended power-up sequence to wake up the device from Backup mode. Upon a Wake-up event (WKUP pin, RTC alarm, etc.), the Shutdown Controller automatically toggles its SHDN output back to VBAT to request the external power supply to restart. This power-up sequence is the same as the one shown in Figure 74-2. In particular, the supply groups definition is the same.

Figure 74-5. Recommended Power Sequence at Wake-Up from Backup Mode

Table 74-13. Wake-Up from Backup Mode Timing Specification⁽¹⁾
Symbol	Parameter	Conditions	Min	Max	Unit
t₀	VDDIN33 delay	Delay from SHDN high to VDDIN33 turn-on	0	–	ms
t₁	VDDIN33 to periphery group delay	Delay from established VDDIN33 to the first established periphery group supply	-0.1	–	ms
t₂	Periphery group to VDDCORE delay	Delay from the last periphery group established supply to VDDCORE supply turn-on	0	–	ms
t₃	Reset delay at power-up	From established VDDCORE to NRST high	8	–	ms

Note:

The term "established" refers to a power supply established at 90% of its final value.