wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 125

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
QUICK START-UP AND SHUTDOWN
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The WM8918 has the capability to perform a quick start-up and shutdown with a minimum number of
register operations. This is achieved using the Control Write Sequencer, which is configured with
default start-up settings that set up the device for DAC playback via Headphone and Line output.
Assuming a 12.288MHz external clock, the start-up sequence configures the device for 48kHz
playback mode.
The default start-up sequence requires three register write operations. The default shutdown
sequence requires just a single register write. The minimum procedure for executing the quick start-
up and shutdown sequences is described below. See “Control Write Sequencer” for more details.
After the default start-up sequence has been performed, the DC offset correction values will be held
in memory, provided that power is maintained and a software reset is not performed. Fast start-up
using the stored values of DC offset correction is also possible, as described below.
QUICK START-UP (DEFAULT SEQUENCE)
An external clock must be applied to MCLK. Assuming 12.288MHz input clock, the start-up sequence
will take approximately 300ms to complete.
The following register operations will initiate the quick start-up sequence.
Table 84 Quick Start-up Control
The WSEQ_BUSY bit (in Register R112, see Table 78) will be set to 1 while the sequence runs.
When this bit returns to 0, the device has been set up and is ready for DAC playback operation.
FAST START-UP FROM STANDBY
The default start-up sequence runs the DC Servo to remove DC offsets from the outputs. The offset
for this path selection is then stored in memory. Provided that power is maintained to the chip, and a
software reset is not performed, then the DC offset correction will be held in memory on the
WM8918. This allows the DC Servo calibrations to be omitted from the start-up sequence if the offset
correction has already been performed. By omitting this part of the start-up sequence, a fast start-up
time of less than 50ms can be achieved.
The register write sequence described in Table 85 replaces the default DC Servo operation with
dummy operations, allowing a fast start-up to be achieved, assuming the device is initially in a
standby condition with DC offset correction previously performed.
R108 (6Ch)
Write Sequencer 0
R111 (6Fh)
Write Sequencer 3
R33 (21h)
DAC Digital 1
REGISTER
ADDRESS
VALUE
0100h
0100h
0000h
WSEQ_ENA = 1
WSEQ_WRITE_INDEX = 00h
This enables the Write Sequencer
WSEQ_ABORT = 0
WSEQ_START = 1
WSEQ_START_INDEX = 00h
This starts the Write Sequencer at Index address 0 (00h)
DAC_MONO = 0
DAC_SB_FILT = 0
DAC_MUTERATE = 0
DAC_UNMUTE_RAMP = 0
DAC_OSR128 = 0
DAC_MUTE = 0
DEEMPH = 00
This un-mutes the DACs
DESCRIPTION
PD, Rev 4.0, September 2010
WM8918
125