
Analog Integrated Circuit Device Data
Freescale Semiconductor
52
PC34708
Functional Block Requirements and Behaviors
Power Control Logic Block Description and Application Information
7.2.7.1
Timing Diagrams
A Turn On event timing diagrams shown in
Figure 9.Figure 9. Power Up Timing Diagram
7.2.8
Power Up
At power up, switchers and regulators are sequentially enabled in time slots of 2.0 ms steps, to limit the inrush current after an
initial delay of 8.0 ms, in which the core circuitry gets enabled. To ensure a proper power up sequence, the outputs of the
switchers that are not enabled are discharged at the beginning of the Cold start with weak pull downs on the output. For that
same reason, a 8.0 ms delay allows the outputs of the linear regulators to be fully discharged as well, through the built in
discharge path. The peak inrush current per event is limited. Any under-voltage detection at BP is masked while the power up
sequencer is running. When the switcher is enabled it will start in PWM mode and for 3.0 ms and then it will switch over to the
mode that it is programmed to in the SPI.
The Power Up Mode Select pins PUMSx (x = 1,2,3,4,5) are used to configure the startup characteristics of the regulators. Supply
enabling and output level options are selected by hardwiring the PUMSx pins for the desired configuration. The recommended
power up strategy for end products is to bring up as little of the system as possible at booting, essentially sequestering just the
bare essentials to allow processor startup and software to run. With such a strategy, the startup transients are controlled at lower
levels, and the rest of the system power tree can be brought up by software. This allows optimization of supply ordering, where
specific sequences may be required, as well as supply default values. Software code can load up all of the required
programmable options, to avoid sneak paths, under/over-voltage issues, startup surges, etc, without any change in hardware.
The state of the PUMSx pins are latched in before any of the switchers or regulators are enabled, with the exception of VCORE.
PUMSx options and startup configurations will be robust to a PCUT event, whether occurring during normal operation or during
the 8.0 ms of pre-sequencer initialization, i.e., the system will not end up in an unexpected / undesirable consumption state.
Table 44 shows the initial setup for the voltage level of the switchers and regulators, and whether they get enabled.
RESETB
WDI
INT
UV Masking
8 ms
20 ms
12 ms
Power Up Sequencer
Turn On Verification
128 ms
2- Cold Start
1- Off
System Core Active
3- Watchdog
4- On
1- Off
3- Watchdog
Power up of the system upon a Turn On Event followed by a transition to the On state if WDI is pulled high
... or transition to Off state if WDI remains low
Turn On Event
Sequencer time slots
WDI Pulled Low
= Indeterminate State
ow
Turn on Event is based on PWRON being pulled low
8 ms