WM8941
Pre Production
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:
1.
2.
3.
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).
4.
5.
6.
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).
7.
Enable speaker outputs (SPKPEN = 1, SPKNEN = 1) and wait for outputs to
settle.
8.
Set VMIDSEL[1:0] bits for 50kΩ reference string impedance.
9.
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.
13.
14.
15.
Enable DAC (DACEN =1) and Speaker Mixer (SPKMIXEN = 1).
Enable output of DAC to speaker mixer (DAC2SPK = 1).
Disable speaker mute (SPKMUTE = 0) and set SPKVOL = -57dB.
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:
1.
2.
3.
4.
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).
5.
6.
7.
8.
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).
9.
Reset all registers to their default state (software reset).
Turn off external power supply voltages.
10.
PP, Rev 3.3, December 2007
72
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
