8.4.2 Backup Mode Entry

The figure below shows the recommended power down sequence to place the device either in Backup mode or in Backup mode with its DDR in self-refresh. The SHDN signal, output of Shutdown Controller (SHDWC), signals the shutdown request to the power supply. This output is supplied by VDDBU that is present in Backup mode. Placing the external DDR memory in self-refresh while in Backup mode, requires to maintain also VDDIODDR. One possible way to signal this additional need to the power supply is to position one of the general purpose I/Os supplied by VDDBU (PIOBUx) in a predefined state.

Figure 8-3. Recommended Backup Mode Entry

Table 8-4. Powerdown Timing Specification
Symbol	Parameter	Conditions	Min	Max	Unit
t_RSTPD	Reset delay at powerdown	From NRST low to the first supply turn-off	0	–	ms