
Analog Integrated Circuit Device Data
Freescale Semiconductor
51
PC34708
Functional Block Requirements and Behaviors
Power Control Logic Block Description and Application Information
7.2.6
Turn Off Events
7.2.6.1
Power Button Press (via WDI)
User shut down of a product is typically done by pressing the power button connected to the PWRONx pin. This will generate an
interrupt (PWRONxI), but will not directly power off the part. The product is powered off by the processor’s response to this
interrupt, which will be to pull WDI low. Pressing the power button is therefore under normal circumstances not considered as a
turn off event for the state machine. However, since the button press power down is the most common turn off method for end
products, it is described in this section as the product implementation for a WDI initiated Turn Off event.
Note that the software can configure a user initiated power down, via a power button press for transition to a Low Power Off mode
(Memory Hold or User Off) for a quicker restart than the default transition into the Off state.
7.2.6.2
Power Button System Reset
A secondary application of the PWRONx pins is the option to generate a system reset. This is recognized as a Turn Off event.
By default, the system reset function is disabled but can be enabled by setting the PWRONxRSTEN bits. When enabled, a 4
second long press on the power button will cause the device to go to the Off mode, and as a result, the entire application will
power down. An interrupt SYSRSTI is generated upon the next power up. Alternatively, the system can be configured to restart
automatically by setting the RESTARTEN bit.
7.2.6.3
Thermal Protection
If the die gets overheated, the thermal protection will power off the part to avoid damage. A Turn On event will not be accepted
while the thermal protection is still being tripped. The part will remain in Off mode until cooling sufficiently to accept a Turn On
event. There are no specific interrupts related to this other than the warning interrupts.
7.2.6.4
Under-voltage Detection
When the voltage at BP drops below the under-voltage detection threshold UVDET, the state machine will transition to Off mode
if PCUT is not enabled, or if the PCT timer expires when PCUT is enabled.
The SDWNB pin is used to notify that the processor that the PMIC is going to immediately shut down. The PMIC will bring the
SDWNB pin low for one 32 kHz clock cycle before powering down. This signal will then be brought back high in the power Off
state.
7.2.7
Timers
The different timers as used by the state machine are listed by the following. This listing does not include RTC timers for
timekeeping. A synchronization error of up to one clock period may occur with respect to the occurrence of an asynchronous
event, the duration listed below is therefore the effective minimum time period.
Table 43. Timer Main Characteristics
Timer
Duration
Clock
Under-voltage Timer
4.0 ms
32 k/32
Reset Timer
40 ms
32 k/32
Watchdog Timer
128 ms
32 k/32
Power Cut Timer
Programmable 0 to 8 seconds
in 31.25 ms steps
32 k/1024