34708 datasheet(35/159 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

Functional Block Description

7.5.2

Modes of Operation

The MC34708 PMIC is fully programmable via the SPI 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 that

it is kept topped off until needed.

The MC34708 PMIC provides the timekeeping, based on an integrated low power oscillator running with a standard watch 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

User

Off

Memory

Hold

Warm

Start

Watchdog

Cold

Start

User Off

Wait

Internal

MemHold

Power

Cut

From any mode: Loss of Power with PCEN=0

Thermal Protection Trip, or System Reset

Unqual’d

Turn On

WDI Low,

WDIRESET=0

Unqual’d

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 Modes

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 Modes

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 mode: 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 Modes 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

34708 Datasheet(PDF) 35 Page - Freescale Semiconductor, Inc

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