WM8941 datasheet(72/96 Pages) WOLFSON

72 / 96 page

WM8941

Pre Production

PP, Rev 3.3, December 2007

RECOMMENDED POWER UP/DOWN SEQENCE

In order to minimise output pop and click noise, it is recommended that the WM8941 device is

powered up and down using one of the following sequences:

Power Up:

Turn on external power supplies. Wait for supply voltages to settle.

Reset internal registers to default state (software reset).

Enable non-VMID derived bias generator (VMID_OP_EN = 1) and level shifters

(LVLSHIFT_EN = 1).

Enable DAC soft mute (DACMU = 1).

Select Clock source to MCLK (CLKSEL = 0) and audio mode (Master or Slave).

Enable Power on Bias Control (POB_CTRL = 1) and VMID soft start

(SOFT_START = 1).

Enable speaker outputs (SPKPEN = 1, SPKNEN = 1) and wait for outputs to

settle.

Set VMIDSEL[1:0] bits for 50kΩ reference string impedance.

Wait for the VMID supply to settle. *Note 2.

10.

Enable analogue amplifier bias control (BIASEN = 1) and VMID buffer (BUFIOEN

= 1). *Notes 1 and 2.

11.

Disable Power on Bias Control (POB_CTRL = 0) and VMID soft start

(SOFT_START = 0).

12.

Enable DAC (DACEN =1) and Speaker Mixer (SPKMIXEN = 1).

13.

Enable output of DAC to speaker mixer (DAC2SPK = 1).

14.

Disable speaker mute (SPKMUTE = 0) and set SPKVOL = -57dB.

15.

Ramp up the SPKVOL using the following values:

-27 dB, -21 dB, -15 dB, -13 dB, -11 dB, -9 dB, -8 dB, -7 dB, -6 dB, -5 dB, -4 dB, -3

dB, -2 dB, -1 dB, 0 dB.

16.

Disable DAC soft mute (DACMU = 0).

Power Down:

Enable DAC soft mute (DACMU = 1).

Enable non-VMID derived bias generator (VMID_OP_EN = 1).

Enable on Bias Control (POB_CTRL = 1).

Disable analogue amplifier bias control (BIASEN = 0) and VMID (VMIDSEL[1:0]

bits set to OFF).

Enable Fast VMID Discharge (TOGGLE = 1) to discharge VMID capacitor.

Wait for VMID capacitor to fully discharge.

Enable speaker output mute (SPKMUTE = 1).

Disable DAC (DACEN = 0), speaker mixer (SPKMIX = 0), and speaker outputs

(SPKPEN = 0 and SPKNEN = 0).

Reset all registers to their default state (software reset).

10.

Turn off external power supply voltages.

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