Ultra Low Power DAC for Portable Audio Applications WM8918 w DESCRIPTION The WM8918 is a high performance ultralow power stereo DAC optimised for portable audio applications The device features stereo groundreferenced headphone amplifiers using the Wolfson ClassW amplifier techniques incorporating an innovative dualmode charge pump architecture to optimise efficiency and power consumption during playback The groundreferenced headphone and line outputs eliminate A......
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DESCRIPTION
The WM8918 is a high performance ultra-low power stereo
DAC optimised for portable audio applications.
The device features stereo ground-referenced headphone
amplifiers using the Wolfson ‘Class-W’ amplifier techniques -
incorporating an innovative dual-mode charge pump
architecture - to optimise efficiency and power consumption
during playback. The ground-referenced headphone and line
outputs eliminate AC coupling capacitors, and both outputs
include common mode feedback paths to reject ground
noise.
Control sequences for audio path setup can be pre-loaded
and executed by an integrated control write sequencer to
reduce software driver development and minimise pops and
clicks via Wolfson’s SilentSwitch™ technology.
The analogue input stage can be configured for single
ended or differential inputs. Up to 3 stereo microphone or
line inputs may be connected. The input impedance is
constant with PGA gain setting.
A stereo digital microphone interface is provided, with a
choice of two inputs. The analogue or digital microphone
inputs can be mixed into the headphone or line output paths.
A dynamic range controller provides compression and level
control to support a wide range of portable recording
applications in conjunction with the digital microphone
interface. Anti-clip and quick release features offer good
performance in the presence of loud impulsive noises.
ReTune
Mobile 5-band parametric equaliser with fully
programmable coefficients is integrated for optimization of
speaker characteristics. Programmable dynamic range
control is also available for maximizing loudness, protecting
speakers from clipping and preventing premature shutdown
due to battery droop.
Common audio sampling frequencies are supported from a
wide range of external clocks, either directly or generated
via the FLL.
The WM8918 can operate directly from a single 1.8V
switched supply. For optimal power consumption, the digital
core can be operated from a 1.0V supply.
TM
WM8918
Ultra Low Power DAC for Portable Audio Applications
FEATURES
3.8mW quiescent power consumption for DAC to
headphone playback
DAC SNR 96dB typical, THD -86dB typical
2.4mW quiescent power consumption for analogue bypass
playback
Control write sequencer for pop minimised start-up and
shutdown
Single register write for default start-up sequence
Integrated FLL provides all necessary clocks
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Self-clocking modes allow processor to sleep
All standard sample rates from 8kHz to 96kHz
Stereo digital microphone input
3 single ended inputs per stereo channel
1 fully differential mic / line input per stereo channel
Digital Dynamic Range Controller (compressor / limiter)
DIFFERENTIAL LINE INPUT ......................................................................................................................................... 31
INPUT PGA GAIN CONTROL ....................................................................................................................................... 32
INPUT PGA COMMON MODE AMPLIFIER .................................................................................................................. 34
MICBIAS CONTROL ...................................................................................................................................................... 35
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PD, Rev 4.1, January 2012
3
WM8918
Production Data
MICBIAS CURRENT DETECT ...................................................................................................................................... 36
MICBIAS CURRENT DETECT FILTERING .................................................................................................................. 37
DIGITAL MICROPHONE INTERFACE .......................................................................... 40
DIGITAL MICROPHONE VOLUME CONTROL............................................................................................................. 42
HIGH PASS FILTER ...................................................................................................................................................... 44
DYNAMIC RANGE CONTROL (DRC) ........................................................................... 45
GAIN LIMITS .................................................................................................................................................................. 47
ANTI-CLIP CONTROL ................................................................................................................................................... 48
QUICK RELEASE CONTROL ....................................................................................................................................... 49
GAIN SMOOTHING ....................................................................................................................................................... 49
RETUNE MOBILE MODE........................................................................................................................................... 52
DIGITAL MIXING ........................................................................................................... 54
DIGITAL MIXING PATHS .............................................................................................................................................. 54
DIGITAL SIDETONE ...................................................................................................................................................... 56
DAC DIGITAL VOLUME CONTROL .............................................................................................................................. 58
DAC SOFT MUTE AND SOFT UN-MUTE ..................................................................................................................... 60
DAC OVERSAMPLING RATIO (OSR) .......................................................................................................................... 62
OUTPUT SIGNAL PATH ............................................................................................... 63
OUTPUT SIGNAL PATHS ENABLE .............................................................................................................................. 64
HEADPHONE / LINE OUTPUT SIGNAL PATHS ENABLE ........................................................................................... 64
OUTPUT MUX CONTROL ............................................................................................................................................. 69
HEADPHONE OUTPUTS – HPOUTL AND HPOUTR ................................................................................................... 72
LINE OUTPUTS – LINEOUTL AND LINEOUTR............................................................................................................ 72
EXTERNAL COMPONENTS FOR GROUND REFERENCED OUTPUTS .................................................................... 73
REFERENCE VOLTAGES AND MASTER BIAS........................................................... 74
POP SUPPRESSION CONTROL .................................................................................. 75
DISABLED INPUT CONTROL ....................................................................................................................................... 75
DC SERVO .................................................................................................................... 77
DC SERVO ENABLE AND START-UP ......................................................................................................................... 77
DC SERVO ACTIVE MODES ........................................................................................................................................ 80
DC SERVO READBACK ............................................................................................................................................... 82
DIGITAL AUDIO INTERFACE ....................................................................................... 82
MASTER AND SLAVE MODE OPERATION ................................................................................................................. 83
OPERATION WITH TDM ............................................................................................................................................... 83
BCLK FREQUENCY ...................................................................................................................................................... 84
AUDIO DATA FORMATS (NORMAL MODE) ................................................................................................................ 84
AUDIO DATA FORMATS (TDM MODE)........................................................................................................................ 87
DIGITAL AUDIO INTERFACE CONTROL..................................................................... 89
BCLK AND LRCLK CONTROL ...................................................................................................................................... 90
DIGITAL PULL-UP AND PULL-DOWN .......................................................................................................................... 93
CLOCKING AND SAMPLE RATES ............................................................................... 95
SYSCLK CONTROL ...................................................................................................................................................... 97
CONTROL INTERFACE CLOCKING ............................................................................................................................ 97
DMIC / DAC CLOCK CONTROL ................................................................................................................................... 98
OPCLK CONTROL ........................................................................................................................................................ 99
TOCLK CONTROL ........................................................................................................................................................ 99
DAC OPERATION AT 88.2K / 96K .............................................................................................................................. 100
FREQUENCY LOCKED LOOP (FLL) .......................................................................... 101
GPIO OUTPUTS FROM FLL ....................................................................................................................................... 105
EXAMPLE FLL CALCULATION................................................................................................................................... 106
EXAMPLE FLL SETTINGS .......................................................................................................................................... 107
GENERAL PURPOSE INPUT/OUTPUT (GPIO) ......................................................... 108
USING IN1L AND IN1R AS INTERRUPT INPUTS ...................................................................................................... 114
CONTROL INTERFACE .............................................................................................. 115
CONTROL WRITE SEQUENCER ............................................................................... 117
INITIATING A SEQUENCE .......................................................................................................................................... 117
PROGRAMMING A SEQUENCE ................................................................................................................................ 118
FAST START-UP FROM STANDBY ........................................................................................................................... 127
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