WM8950 datasheet(39/52 Pages) WOLFSON

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Preliminary Technical Data

WM8950

PTD Rev 2.1 June 2005

SDIN

SCLK

1st register data bit

DEVICE ADDRESS

(7 BITS)

RD / WR

BIT

ACK

(LOW)

CONTROL BYTE 1

(BITS 15 TO 8)

CONTROL BYTE 1

(BITS 7 TO 0)

remaining 8 bits of

STOP

START

ACK

(LOW)

ACK

(LOW)

Figure 25 2-Wire Serial Control Interface

In 2-wire mode the WM8950 has a fixed device address, 0011010.

RESETTING THE CHIP

The WM8950 can be reset by performing a write of any value to the software reset register (address

0 hex). This will cause all register values to be reset to their default values. In addition to this there

is a Power-On Reset (POR) circuit which ensures that the registers are set to default when the

device is powered up.

POWER SUPPLIES

The WM8950 can use up to three separate power supplies:

AVDD, AVDD2, AGND and AGND2: Analogue supply, powers all analogue functions. AVDD can

range from 2.5V to 3.6V and has the most significant impact on overall power consumption. A large

AVDD slightly improves audio quality.

DCVDD: Digital core supply, powers all digital functions except the audio and control interfaces.

DCVDD can range from 1.71V to 3.6V, and has no effect on audio quality. The return path for

DCVDD is DGND, which is shared with DBVDD.

DBVDD Can range from 1.71V to 3.6V. DBVDD return path is through DGND.

It is possible to use the same supply voltage for all supplies. However, digital and analogue supplies

should be routed and decoupled separately on the PCB to keep digital switching noise out of the

analogue signal paths.

POWER MANAGEMENT

SAVING POWER BY REDUCING OVERSAMPLING RATE

The default mode of operation of the ADC digital filters is in 64x oversampling mode. Under the

control of ADCOSR the oversampling rate may be doubled. 64x oversampling results in a slight

decrease in noise performance compared to 128x but lowers the power consumption of the device.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R14

ADC control

ADCOSR128

ADC oversample rate select

0 = 64x (lowest power)

1 = 128x (best SNR)

Table 34 ADC Oversampling Rate Selection

VMID

The analogue circuitry will not work unless VMID is enabled (VMIDSEL 00). The impedance of the

VMID resistor string, together with the decoupling capacitor on the VMID pin will determine the

startup time of the VMID circuit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 1

1:0

VMIDSEL 00

Reference string impedance to VMID pin

(detemines startup time):

00=off (open circuit)

01=75kΩ

10=300kΩ

11=2.5kΩ (for fastest startup)

Table 35 VMID Impedance Control

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