8.2 Power-up Considerations

At power-up, from a supply sequencing perspective, the power supply inputs are categorized into two groups:

  • Group 1 (core group) contains VDDCORE, VDDUTMIC, VDDHSIC and VDDPLLA.
  • Group 2 (periphery group) contains all other power supply inputs except VDDFUSE.
    The figure below shows the recommended power-up sequence. Note that:
    • VDDBU, when supplied from a battery, is an always-on supply input and is therefore not part of the power supply sequencing. When no backup battery is present in the application, VDDBU is part of Group 2.
    • VDDFUSE is the only power supply that may be left unpowered during operation. This is possible if and only if the application does not access the Customer Fuse Matrix in Write mode. It is good practice to turn on VDDFUSE only when the Customer Fuse Matrix is accessed in Write mode, and to turn off VDDFUSE otherwise.
    • VDDIODDR may be nominally supplied at 1.2V when the device is equipped with an LPDDR2 or LPDDR3 memory. In this case, VDDIODDR can be considered as part of Group 1.
Figure 8-1. Recommended Power-up Sequence
Table 8-2. Power-up Timing Specification
Symbol Parameter Conditions Min Max Unit
t1 Group 2 to Group 1 delay Delay from the last Group 2 established(1) supply to the first Group1 supply turn-on 0 – ms
t2 Group 1 delay(2) Delay from the first group 1 established supply to the last Group 1 established supply – 1
t3 VDDFUSE to VDDBU delay Delay from VDDBU established to VDDFUSE turn-on 1 –
tRSTPU Reset delay at power-up From the last established supply to NRST high 1 –
Note:
  1. An “established” supply refers to a power supply established at 90% of its final value.
  2. Also applies to VDDIODDR when considered as part of Group 1.