WM8974 datasheet(14/63 Pages) WOLFSON

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WM8974

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PP Rev 1.1 September 2004

CONTROL INTERFACES

To allow full software control over all its features, the WM8974 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 selection between 2-wire mode and 3-wire mode is

determined by the state of the MODE pin. If MODE is high then 3-wire control mode is selected, if

MODE is low then 2-wire control mode is selected.

In 2 wire mode, only slave operation is supported, and the address of the device is fixed as 0011010.

CLOCKING SCHEMES

WM8974 offers the normal audio DAC clocking scheme operation, where 256fs MCLK is provided to

the DAC/ADC.

However, a PLL is also included which may be used to generate the internal master clock frequency

in the event that this is not available from the system controller. This PLL uses an input clock,

typically the 12MHz USB or ilink clock, to generate high quality audio clocks. If this PLL is not

required for generation of these clocks, it can be reconfigured to generate alternative clocks which

may then be output on the CSB/GPIO pin and used elsewhere in the system.

POWER CONTROL

The design of the WM8974 has given much attention to power consumption without compromising

performance. It operates at low supply voltages, and includes the facility to power off any unused

parts of the circuitry under software control, includes standby and power off modes.

INPUT SIGNAL PATH

The WM8974 has 3 flexible analogue inputs: two microphone inputs, and an auxiliary input. These

inputs can be used in a variety of ways. The input signal path before the ADC has a flexible PGA

block which then feeds into a gain boost/mixer stage.

MICROPHONE INPUTS

The WM8974 can accommodate a variety of microphone configurations including single ended and

differential inputs.

The inputs through the MICN, MICP and optionally AUX pins are amplified

through the input PGA as shown in Figure 6.

A differential input is the preferential configuration where the positive terminal of the input PGA is

connected to the MICP input pin by setting MICP2INPPGA=1. The other microphone terminal should

then be connected to MICN (when MICN2INPPGA=1) or optionally to AUX (when AUX2INPPGA=1)

input pins.

Single ended microphone inputs should connect to the MICP input with MICP2INPPGA set to 1. The

negative terminal of the input PGA should be connected to VMID externally through a cap. This is

achieved by setting register bit MICN2INPPGA=1.

Alternatively a single ended microphone can be connected to the MICN input with MICN2INPPGA set

to 1.

The positive terminal of the input PGA should be connected internally to VMID by setting

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