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WM8974

PP Rev 1.1 September 2004

RECOMMENDED POWER UP/DOWN SEQENCE

In order to minimise output ‘pop’ and ‘click’ noise it is recommended that the device is powered up in

a controlled sequence.

In addition to this it is recommended that the zero cross functions are used when changing the

volume in the PGAs.

POWER MANAGEMENT

SAVING POWER BY REDUCING OVERSAMPLING RATE

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

Under the control of ADCOSR and DACOSR 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

R10

DAC control

DACOSR128

DAC oversample rate select

0 = 64x (lowest power)

1 = 128x (best SNR)

R14

ADC control

ADCOSR128

ADC oversample rate select

0 = 64x (lowest power)

1 = 128x (best SNR)

Table 42 ADC and DAC 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 43 VMID Impedance Control

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