WM8955BL
Production Data
DEVICE DESCRIPTION
INTRODUCTION
The WM8955BL is a low power audio DAC offering a combination of high quality audio, advanced
features, low power and small size. These characteristics make it ideal for portable digital audio
applications such as portable music players and smartphones.
The device has a configurable digital audio interface where digital audio data is fed to the internal
digital filters and then the DAC. The interface supports a number of audio data formats including I2S,
DSP Mode (a burst mode in which frame sync plus 2 data packed words are transmitted), Left
Justified and Right Justified formats, and can operate in master or slave modes.
The on-chip digital filters perform tone control and digital volume control according to the user setting,
and convert the audio data into oversampled bitstreams, which are passed to the left and right
channel DACs. A multi-bit, low-order ΣΔ DAC architecture with dynamic element matching is used,
delivering optimum performance with low power consumption.
The DAC output signal enters an analogue mixer where analogue input signals can be added to it.
The WM8955BL has a total of six analogue output pins, which can be configured as stereo line-outs,
mono line-outs, differential mono line-outs, stereo headphone outputs or differential mono (BTL)
earpiece outputs.
The WM8955BL includes an on-chip PLL to generate commonly used audio rates, such as 48kHz
and 44.1kHz, from system clocks found in GSM, CDMA and PDC phones and other portable
systems.
To allow full software control over all its features, the WM8955BL offers a choice of 2 or 3 wire MPU
control interface. It is fully compatible and an ideal partner for a wide range of industry standard
microprocessors, controllers and DSPs.
The design of the WM8955BL has given much attention to power consumption without compromising
performance. It operates at very low voltages, and includes the ability to power off parts of the
circuitry under software control, including standby and power off modes.
SIGNAL PATH
The WM8955BL signal paths consists of digital filters, DACs, analogue mixers and output drivers.
Each circuit block can be enabled or disabled separately using the control bits in register 26 (see
“Power Management”). Thus it is possible to utilise the analogue mixing and amplification provided by
the WM8955BL, irrespective of whether the DACs are running or not.
The WM8955BL receives digital input data on the DACDAT pin. The digital filter block processes the
data to provide the following functions:
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Digital volume control
Tone control and Bass Boost
Digital Mono Mix
Sigma-Delta Modulation
Two high performance, sigma-delta audio DACs convert the digital data into two analogue signals
(left and right). These can then be mixed with analogue signals from the LINEINL, LINEINR and
MONOIN pins, and the mix is fed to the output drivers, LOUT1/ROUT1, LOUT2/ROUT2, MONOOUT
and OUT3.
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LOUT1/ROUT1: can drive 16Ω or 32Ω stereo headphones or stereo line output.
LOUT2/ROUT2: can drive a 32Ω earpiece, stereo headphones or a stereo line-out.
MONOOUT: line output designed to drive a 10kΩ load.
OUT3: multi-function output, may be used for capacitor-less headphone drive, differential
mono-out, line-out or 32Ω earpiece driver.
PD Rev 4.1 February 2007
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
