Pre-Production
WM8940
It is possible to use the same supply voltage for all four 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.
RECOMMENDED POWER UP/DOWN SEQUENCE
In order to minimise output pop and click noise, it is recommended that the WM8940/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
(LVLSHIFT_EN = 1).
= 1) and level shifters
4.
5.
6.
7.
8.
9.
10.
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 75kΩ reference string impedance.
Wait for the VMID supply to settle. *Note 2.
Enable analogue amplifier bias control (BIASEN = 1) and VMID buffer (BUFIOEN = 1).
*Notes 1 and 2.
11.
12.
13.
14.
15.
16.
Disable Power on Bias Control (POB_CTRL = 0) and VMID soft start (SOFT_START = 0).
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.
17.
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.
Enable Fast VMID Discharge (TOGGLE = 1) to discharge VMID capacitor.
Wait for VMID capacitor to fully discharge.
Enable speaker output mute (SPKMUTE = 1).
Pre-Production, Rev 3.0, February 2007
63
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
