wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 52

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

WM8400
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AUDIO CODEC SUBSYSTEM
INTRODUCTION
The WM8400 incorporates a low power, high quality audio CODEC which is designed to interface
with a wide range of processors and analogue components.
Eight highly flexible analogue inputs allow interfacing to up to four microphone inputs plus multiple
stereo or mono line inputs (single-ended or differential). Connections to an external voice CODEC,
FM radio, melody IC, line input, handset MIC and headset MIC are all fully supported. Signal routing
to the output mixers and within the CODEC has been designed for maximum flexibility to support a
wide variety of usage modes.
Ten analogue output drivers are integrated, including a high power, high quality speaker driver,
capable of providing 1W in class D mode or 0.5W in class AB mode into 8Ω BTL. Four headphone
drivers are provided, supporting ear speakers and stereo headsets. Fully differential headphone drive
is supported for excellent crosstalk performance and removing the need for large and expensive
headphone capacitors. Four line outputs are available for Tx voice output to a voice CODEC,
interfacing to an additional speaker driver and single-ended or fully differential line output. All outputs
have integrated pop and click suppression. The speaker supply has been designed with low leakage
and high PSRR, to support direct connection to a Lithium battery. Six AC and DC gain settings allow
output signal levels to be maximised for a number of AVDD and SPKVDD combinations.
Internal signal routing and amplifier configurations have been optimised to provide the lowest
possible power consumption for a number of common usage scenarios such as voice calls and
music playback.
The stereo ADCs and DACs are of hi-fi quality using a 24-bit, low-order oversampling architecture to
deliver optimum performance. A flexible clocking arrangement supports mixed ADC and DAC sample
rates, while an integrated ultra-low power FLL provides additional flexibility. A high pass filter is
available in the ADC path for removing DC offsets or suppressing low frequency noise such as
mechanical vibration and wind noise. A digital mixing path from the ADC to the DAC provides a
sidetone of enhanced quality during voice calls. Pop-free DAC soft mute and un-mute is available.
The WM8400 has a highly flexible digital audio interface, supporting a number of protocols, including
I
supported in the DSP mode. A-law and µ-law companding are also supported. Time division
multiplexing (TDM) is available to allow multiple devices to stream data simultaneously on the same
bus, saving space and power. Alternative DAC interface pins are provided to allow connection to an
additional processor.
The SYSCLK (system clock) provides clocking for the ADCs, DACs, DSP core, class D outputs and
the digital audio interface. SYSCLK can be derived directly from the MCLK pin or via an integrated
FLL, providing flexibility to support a wide range of clocking schemes. All MCLK frequencies typically
used in portable systems are supported for sample rates between 8kHz and 48kHz. The switching
clock for the class D speaker drivers can be derived from SYSCLK or else provided by an oscillator
within the WM8400. (Best speaker driver performance is achieved when this clock is synchronous
with the audio DSP clocks.) An additional master clock input pin is provided, to support operation on
an alternative clock domain, selectable via a de-glitch circuit.
Versatile GPIO functionality is provided, with support for up to seven button/accessory detect inputs
with interrupt and status readback and flexible de-bouncing options, clock output, alternative MCLK
input, ADCLRC inversion for simultaneous streaming of ADC data to two separate processors and
logic '1' / logic '0' for control of additional external circuitry.
Unused circuit blocks within the CODEC can be disabled via software to save power, while low
leakage currents extend standby and off time in portable battery-powered applications.
2
S, DSP, MSB-First left/right justified, and can operate in master or slave modes. PCM operation is
PP, April 2009, Rev 3.0
Pre-Production
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