Figure 6-8 depicts the power sequencing requirements for external VREG mode. The values for
all the parameters indicated can be found in Power Management Module Electrical Data
and Timing.
- For Power Up:
- VDDIO (that is, the 3.3-V
rail) should come up first with the minimum slew rate specified.
- VDD (that is, the 1.2-V
rail) should come up next with the minimum slew rate specified.
- The time delta between
the VDDIO rail coming up and when the VDD rail can come up is also
specified.
- After the times specified
by VDDIO-MON-TOT-DELAY and VXRSN-PD-DELAY, XRSn
will be released and the device starts the boot-up sequence.
There is an additional delay between XRSn releasing (that is, going
high) and the boot-up sequence starting. See Figure 6-6.
- The I/O BOR monitor has
different release points during power up and power down.
- During power up, both
VDDIO and VDD rails have to be up before XRSn releases.
- For Power Down:
- There is no requirement
between VDDIO and VDD on which should power down first; however, there
is a minimum slew rate specification.
- The I/O BOR monitor has
different release points during power up and power down.
- Any of the POR or BOR
monitors that trips during power down will cause XRSn to go low after
VXRSN-PD-DELAY.
Note: The All Monitors Release
Signal is an internal signal.
Note: If there is an external circuit
driving XRSn (for example, a supervisor), the boot-up sequence does not start until
the XRSn pin is released by all internal and external sources.