WM8351 datasheet(105/330 Pages) WOLFSON

105 / 330 page

Production Data

WM8351

PD, April 2012, Rev 4.5

105

14 POWER MANAGEMENT SUBSYSTEM

14.1 GENERAL DESCRIPTION

The WM8351 provides five DC-DC Converters and four LDO Regulators which each deliver high

efficiency across a wide range of line and load conditions. These power management components

are designed to support application processors and associated peripherals. They are also suitable for

providing power to the analogue and digital functions of the on-board CODEC and GPIO features.

The output voltage of each of the converters and regulators is programmable in software through

control registers.

The WM8351 has a number of operating states which are either selected by software control or are

selected autonomously according to the available power supply conditions. A low power active

‘Hibernate’ state is provided, with programmable characteristics. The ‘Backup’ and ‘Zero’ states are

selected autonomously when the available supply voltages do not permit full operation of the

WM8351.

Four configuration modes are provided, selected by hardware control. Development Mode gives

complete control over the configuration and start-up behaviour of the WM8351. Three different

Custom Modes each have a defined set of configuration parameters, which determine the start-up

timing and output voltage of each of the DC-DC Converters and LDO Regulators. The configuration of

each of the GPIO pins is also contained with the configuration modes definitions.

14.2 POWER MANAGEMENT OPERATING STATES

The WM8351 autonomously controls the power-up and power-down sequencing for itself and for

other connected devices. It also selects the most appropriate power source available at any given

time (see Section 17). The stable states of the WM8351 are:

ACTIVE

- All WM8351 functions can be used. The WM8351 enters the ACTIVE state after a valid

start-up event (see Section 14.3.1), provided that no fault condition occurred during start-up.

HIBERNATE

- This is an alternative active state with programmable characteristics, allowing an

optional low power system condition. The internally generated supply voltages can be individually

enabled or disabled as desired. The WM8351 enters the HIBERNATE state from ACTIVE by setting

the HIBERNATE register bit or when commanded via a GPIO pin configured as a HIBERNATE

alternate function.

OFF

- All DC-DC converters and regulators LDO2, LDO3 and LDO4 are disabled. LDO1 may remain

active (See Section 14.7.4). The VRTC regulator remains active and powers the always-on functions

(such as crystal oscillator and RTC.) Register settings are restored to default settings. Trickle

charging for the main battery is enabled by default. The WM8351 enters the OFF state from ACTIVE

if a shutdown event occurs (see Section 14.3.3), or if the power source falls below the shutdown

threshold (see Section 18). The WM8351 enters the OFF state from BACKUP if a power source

greater than the UVLO threshold becomes available.

BACKUP

- The crystal oscillator and RTC are enabled, powered from the backup power (VRTC)

supply. All other functions are disabled. The WM8351 enters the BACKUP state from OFF if the

power source falls below the UVLO threshold (see Section 18), and provided that backup power

(VRTC) is available (i.e. LINE falls below the UVLO level but VRTC remains above the Power-On

Reset threshold).

ZERO

- All functions are disabled and all data in registers is lost. The WM8351 goes into this state

when no power source is available and VRTC falls below the Power-On Reset threshold.

The Active state can only be entered via the PRE-ACTIVE state. In Development Mode, the Pre-

Active state is the state in which the WM8351 start-up parameters may be defined, prior to the start-

up sequence being triggered. The ACTIVE state is only entered on completion of the start-up

sequence.

The WM8351 operating states and valid transitions are illustrated in Figure 64.

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