Datasheet

Analog Integrated Circuit Device Data
Freescale Semiconductor 36
MC34708
Functional Block Description
7.5.2 Modes of Operation
The MC34708 PMIC is fully programmable via the SPI/I
2
C interface and associated register map. Additional communication is
provided by direct logic interfacing, including interrupt, watchdog, and reset. Default startup of the device is selectable by
hardwiring the Power Up Mode Select (PUMS) pins.
Power cycling of the application is driven by the MC34708 PMIC. It has the interfaces for the power buttons and dedicated
signaling interfacing with the processor. It also ensures the supply of the Real Time Clock (RTC), critical internal logic, and other
circuits from the coin cell, in case of brief interruptions from the main battery. A charger for the coin cell is included to ensure it
is kept topped off until needed.
The MC34708 PMIC provides the timekeeping, based on an integrated low power oscillator running with a standard crystal. This
oscillator is used for internal clocking, the control logic, and as a reference for the switcher PLL. The timekeeping includes time
of day, calendar, and alarm, and is backed up by coin cell. The clock is driven to the processor for reference and deep sleep
mode clocking.
Figure 6. Power Control State Machine Flow Diagram
Off
On
User
Off
Memory
Hold
Warm
Start
Watchdog
Cold
Start
User Off
Wait
Internal
MemHold
Power
Cut
From any state: Loss of Power with PCEN=0
Thermal Protection Trip, or System Reset
Unqual’d
Turn On
WDI Low,
WDIRESET=0
Unqual’d
Turn On
Turn On
Event
PCT[7:0] Expired
WDI Low
WDIRESET=1
and PCMAXCNT
is exceeded
WDI Low
WDIRESET=1
and PCMAXCNT
is not exceeded
Start Up States
Reset Timer
Expired
Reset Timer
Expired
Watchdog Timer
Expired
Turn On Event
(Warm Boot)
Turn On Event
(Warm Start)
Processor Request
for User Off:
USEROFFSPI=1
PCUT Timeout
PCT[7:0]
Expired
PCUTEXPB
cleared to 0
Low Power
Off States
Warm Start
Enabled
Warm Start
Not
Enabled
WARMEN=1
WARMEN=0
Application of Power
before PCUT Timer
PCT[7:0] expiration
(PCEN=1 and
PCMAXCNT not
exceeded)
From any state: Loss of Power
with Power Cuts enabled
(PCEN=1) and PCMAXCNT
not exceeded
Legend and Notes (refer to text for additional details)
Blue Box = Steady State, no specific timer is running
Green Circle = Transitional State, a specific timer is running, see text
Dashed Boxes = Grouping of States for clarification
WDI has influence only in the “On” state
Complete loss of BP and coin cell power is not represented in the state machine