WM8987LGECOSLASHV datasheet(16/58 Pages) WOLFSON

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WM8987L

Pre-Production

PP Rev 3.0 January 2007

DEVICE DESCRIPTION

INTRODUCTION

The WM8987L is a low power audio codec 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 MP3 and minidisk player / recorders. Stereo 24-bit multi-bit delta sigma ADCs

and DACs are used with oversampling digital interpolation and decimation filters.

The device includes three stereo analogue inputs that can be switched internally. Each can be used

as either a line level input or microphone input and LINPUT1/RINPUT1 and LINPUT2/RINPUT2 can

be configured as mono differential inputs. A programmable gain amplifier with automatic level control

(ALC) keeps the recording volume constant. The on-chip stereo ADC and DAC are of a high quality

using a multi-bit, low-order oversampling architecture to deliver optimum performance with low power

consumption.

The DAC output signal first enters an analogue mixer where an analogue input and/or the post-ALC

signal can be added to it. This mix is available on line and headphone outputs.

The WM8987L has a configurable digital audio interface where ADC data can be read and digital

audio playback data fed to the DAC. It supports a number of audio data formats including I

2S, DSP

Mode (a burst mode in which frame sync plus 2 data packed words are transmitted), and MSB-First,

left justified. It can operate in master or slave modes.

The WM8987L uses a unique clocking scheme that can generate many commonly used audio

sample rates from either a 12.00MHz USB clock or an industry standard 256/384 fs clock. This

feature eliminates the common requirement for an external phase-locked loop (PLL) in applications

where the master clock is not an integer multiple of the sample rate. Sample rates of 8kHz,

11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz, 88.2kHz and 96kHz can be

generated. The digital filters used for recording and playback are optimised for each sampling rate

used.

To allow full software control over all its features, the WM8987L 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 WM8987L 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.

INPUT SIGNAL PATH

The input signal path for each channel consists of a switch to select between three analogue inputs,

followed by a PGA (programmable gain amplifier) and an optional microphone gain boost. A

differential input of either (LINPUT1 – RINPUT1) or (LINPUT2 – RINPUT2) may also be selected.

The gain of the PGA can be controlled either by the user or by the on-chip ALC function (see

Automatic Level Control).

The signal then enters an ADC where it is digitised. Alternatively, the two channels can also be

mixed in the analogue domain and digitised in one ADC while the other ADC is switched off. The

mono-mix signal appears on both digital output channels.

SIGNAL INPUTS

The WM8987L has two sets of high impedance, low capacitance AC coupled analogue inputs,

LINPUT1/RINPUT1 and LINPUT2/RINPUT2. Inputs can be configured as microphone or line level by

enabling or disabling the microphone gain boost.

LINSEL and RINSEL control bits (see Table 4) are used to select independently between external

inputs and internally generated difference signals (LINPUT1-RINPUT1 or LINPUT2-RINPUT2). The

choice of difference signal, LINPUT1-RINPUT1 or LINPUT2-RINPUT2 is made using the DS bit (see

below).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R31 (1Fh)

ADC Input Mode

Differential input select

0: LINPUT1 - RINPUT1

1: LINPUT2 – RINPUT2

Table 3 Differential Input Select

WM8987LGECO/V Datasheet(PDF) 16 Page - Wolfson Microelectronics plc

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