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WM8731 / WM8731L
Portable Internet Audio CODEC with Headphone Driver
and Programmable Sample Rates
WOLFSON MICROELECTRONICS plc
www.wolfsonmicro.com
Production Data, April 2004, Rev 3.4
Copyright 2004 Wolfson Microelectronics plc
DESCRIPTION
The WM8731 or WM8731L (WM8731/L) are low power
stereo CODECs with an integrated headphone driver. The
WM8731/L is designed specifically for portable MP3 audio
and speech players and recorders. The WM8731 is also
ideal for MD, CD-RW machines and DAT recorders.
Stereo line and mono microphone level audio inputs are
provided, along with a mute function, programmable line
level volume control and a bias voltage output suitable for
an electret type microphone.
Stereo 24-bit multi-bit sigma delta ADCs and DACs are
used with oversampling digital interpolation and decimation
filters. Digital audio input word lengths from 16-32 bits and
sampling rates from 8kHz to 96kHz are supported.
Stereo audio outputs are buffered for driving headphones
from a programmable volume control, line level outputs are
also provided along with anti-thump mute and power
up/down circuitry.
The device is controlled via a 2 or 3 wire serial interface.
The interface provides access to all features including
volume controls, mutes, de-emphasis and extensive power
management facilities. The device is available in a small 28-
pin SSOP package or the smaller 28 lead quad flat leadless
package (QFN).
FEATURES
• Highly Efficient Headphone Driver
• Audio Performance
- ADC SNR 90dB (‘A’ weighted) at 3.3V, 85dB at 1.8V
- DAC SNR 100dB (‘A’ weighted) at 3.3V, 95dB at 1.8V
• Low Power
- Playback only 22mW, 8mW (‘L’ Variant)
- Analogue Pass Through 12mW, 3.5mW (‘L’ variant)
- 1.42 – 3.6V Digital Supply Operation
- 2.7 – 3.6V Analogue Supply Operation
- 1.8 – 3.6V Analogue Supply Operation (‘L’ Variant)
• ADC and DAC Sampling Frequency: 8kHz – 96kHz
• Selectable ADC High Pass Filter
• 2 or 3-Wire MPU Serial Control Interface
• Programmable Audio Data Interface Modes
- I
2
S, Left, Right Justified or DSP
- 16/20/24/32 bit Word Lengths
- Master or Slave Clocking Mode
• Microphone Input and Electret Bias with Side Tone Mixer
• Available in 28-Pin SSOP or 28-pin QFN package
APPLICATIONS
• Portable MP3 Players and Recorders
• CD and Minidisc Recorders
• PDAs / smartphones
BLOCK DIAGRAM
MUX
MUX
VOL
VOL
ADC
ADC
DIGITAL
FILTERS
DIGTAL AUDIO INTERFACE
CONTROL INTERFACE
DAC
DAC
VOL/
MUTE
VOL/
MUTE
H/P
DRIVER
H/P
DRIVER
CSB
SDIN
SCLK
Σ
Σ
RHPOUT
LHPOUT
ROUT
LOUT
RLINEIN
LLINEIN
VMID
DBVDD
DGND
AVDD
AGND
0dB/
20dB
MICIN
+12 to -34.5dB, 1.5dB
Steps
CLKOUT
+6 to -73dB
1 dB Steps
HPVDD
HPGND
+6 to -73dB
1 dB Steps
DCVDD
ADCLRC
DACLRC
BCLK
DACDAT
ADCDAT
OSC
XTI/MCLK
XTO
MODE
MICBIAS
MUTE
Bypass
Bypass
CLKIN
DIVIDER
(Div x1, x2)
CLKOUT
DIVIDER
(Div x1, x2)
ATTEN/
MUTE
MUTE
MUTE
ATTEN/
MUTE
MUTE
MUTE
MUTE
MUTE
MUTE
+12 to -34.5dB, 1.5dB
Steps
Side Tone
Side Tone
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WM8731
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