WM8321 datasheet(31/253 Pages) WOLFSON

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Production Data

WM8321

PD, February 2012, Rev 4.0

Note that a transition from the SLEEP state to the OFF state is not a controlled transition. If an ‘OFF’

event occurs whilst in the SLEEP state, then the WM8321 will select the OFF state, but all the

enabled converters and regulators will be disabled immediately; the time-controlled sequence is not

implemented in this case. See Section 11.3 for details of the WM8321 ‘OFF’ events.

The current power state of the WM8321 can be read from the MAIN_STATE register field. A restricted

definition of this field is shown in Table 1. Note that other values of MAIN_STATE are defined for

transition states, but it is recommended that only the values quoted below should be used to confirm

power state transitions.

A power state transition to the BACKUP, SLEEP, ON or OFF state is indicated by the Interrupt bits

described in Section 11.4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16397

(400Dh)

System

Status

4:0

MAIN_STATE [4:0]

0_0000

Main State Machine condition

0_0000 = OFF

0_1011 = PROGRAM

1_1100 = SLEEP

1_1111 = ACTIVE (ON)

Table 1 Power State Readback

11.3 POWER STATE CONTROL

The OFF, ON, SLEEP and WAKE sequences are initiated by many different conditions. When such a

condition occurs, the WM8321 schedules a series of 5 timeslots, enabling a sequence of

enable/disable events to be controlled. The nominal duration of the timeslots is fixed at 2ms, though

this may be extended if any selected circuit has not started up within this time, as described later in

this section. The OFF, SLEEP and WAKE sequences commence after a programmable delay set by

PWRSTATE_DLY. This allows a host processor to request a WM8321 state transition and then

complete other tasks before the transition actually occurs.

The ON sequence is the transition from OFF to ON power states. Each LDO and each DC-DC

Converter may be associated with any one of the available timeslots in the ON sequence. This

determines the time, within the sequence, at which that DC-DC Converter or LDO will be enabled

following an ‘ON’ event.

The clock output (CLKOUT) and GPIO pins configured as External Power Enable (EPE) outputs can

also be associated with any one of the available timeslots in the ON sequence. The EPE function is a

logic output that may be used to control external circuits, including external DC-DC converters.

An example ‘ON’ state transition sequence is illustrated in Figure 5. Each of the DC-DC Converters

and LDO regulators can be individually assigned to one of the five timeslots (shown as T1, T2, T3,

T4, T5), providing total flexibility in the power sequence.

Figure 5 Example Control Sequence for ‘ON’ State Transition

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