Figure 6-6
describes the device power-down sequencing.
- Time Stamp Markers
T0 – MCU_PORz & PORz assert low
to put all processor resources in safe state.
(0ms)
T1 – Main DDR, SRAM Core & SRAM
CPU power supplies start ramp-down.
(0.5ms)
T2 – Low voltage core supplies start
supply ramp-down. (2.5ms)
T3 - 1.8V voltages
start supply ramp-down. (3.0ms)
T4 – 3.3V
voltages start supply ramp-down. (3.5ms)
- Any MCU
or Main dual voltage IO supplies (VDDSHVn_MCU or
VDDSHVn) being supplied by 3.3V to support 3.3V
digital interfaces
- Any MCU
or Main dual voltage IO supplies (VDDSHVn_MCU or
VDDSHVn) being supplied by 1.8V to support 1.8V
digital interfaces. When eMMC memories are used,
Main 1.8V supplies could have a ramp-down aligned
to T1 due to PDN designs grouping supplies with
VDD_MMC0.
- VDDSHV5
supports MMC1 signaling for SD memory cards. A
dual voltage (3.3V/1.8V) power rail is required
for compliant, high-speed SD card operations. If
compliant highspeed SD card operation is needed,
then an independent, dual voltage (3.3V/1.8V)
power source and rail are required. The start of
ramp-down from 3.3V/1.8V will be same as other
3.3V domains as shown. If SD card is not needed or
standard data rates with fixed 3.3V operation is
acceptable, then domain can be grouped with
digital IO 3.3V power rail. If a SD card is
capable of operating with fixed 1.8V, then domain
can be grouped with digital IO 1.8V power
rail.
- VDDA_3P3_USB is 3.3V analog domain used for USB
2.0 differential interface signaling. A low noise,
analog supply is recommended to provide best
signal integrity for USB data eye mask compliance.
The start of ramp-down from 3.3V will be same as
other 3.3V domains as shown. If USB interface is
not needed or data bit errors can be tolerated,
then domain can be grouped with 3.3V digital IO
power rail either directly or through a supply
filter.
- VDDA_1P8_<phy> are 1.8V analog domains
supporting multiple serial PHY interfaces. A low
noise, analog supply is recommended to provide
best signal integrity, interface performance and
spec compliance. If any of these interfaces are
not needed, data bit errors or non-compliant
operation can be tolerated, then domains can be
grouped with digital IO 1.8V power rail either
directly or through an in-line supply filter is
allowed.
- VDD_MMC0
is 1.8V digital supply supporting MMC0 signaling
for eMMC interface and must ramp-down at time
stamp T1 before VDD_CORE starts ramp-down. Any MCU
or Main dual voltage IO operating at 1.8V can be
grouped with VDD_MMC0 into a common power rail
with power down time stamp T1. If MMC0 or eMMC0
interface is not needed, then domain can be
grouped with digital IO 1.8V power rail and
ramp-down at time stamp T3.
- VDD_MCU
is a digital voltage supply with a wide operating
voltage range and power sequencing flexibility,
enabling it to be grouped and ramped-down with
either 0.8V VDD_CORE at time stamp T2 or 0.85V RAM
array domains (VDDAR_xxx) at time stamp T1.
- VDDA_1P8_<clk/pll/ana> are 1.8V analog
domains supporting clock oscillator, PLL &
analog circuitry needing a low noise supply for
optimal performance. It is not recommended to
combine analog VDDA_1P8_<phy> domains or
digital VDDSHVn_MCU and VDDSHVn IO domains since
high frequency switching noise could negatively
impact jitter performance of clock, PLL and DLL
signals.
- MCU_PORz
and PORz must be asserted low for TΔ1 = 200us min
to ensure SoC resources enter into safe state
before any voltage begins to ramp down.