WM8326 Datasheet, PDF (31/255 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

Production Data
WM8326
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 WM8326 ‘OFF’ events.
The current power state of the WM8326 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
R16397
(400Dh)
System
Status
BIT
LABEL
4:0 MAIN_STATE [4:0]
Table 1 Power State Readback
DEFAULT
0_0000
DESCRIPTION
Main State Machine condition
0_0000 = OFF
0_1011 = PROGRAM
1_1100 = SLEEP
1_1111 = ACTIVE (ON)
11.3 POWER STATE CONTROL
The OFF, ON, SLEEP and WAKE sequences are initiated by many different conditions. When such a
condition occurs, the WM8326 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 WM8326 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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PD, June 2012, Rev 4.0
31