Pre-Production
WM8985
RECOMMENDED POWER UP/DOWN SEQUENCE
In order to minimise output pop and click noise, it is recommended that the WM8985 device is
powered up and down under control using the following sequences:
Power Up:
1. Turn on external power supplies. Wait for supply voltage to settle.
2. Set low analogue bias mode, BIASCUT = 1
3. Enable thermal shutdown TSDEN = TSOPCTRL = 1
4. Enable Internal bias BIASEN = 1.
5. Mute all outputs and set PGAs to minimum gain, R52 to R57 = 0x140h.
6. Enable VMID independent current bias, POBCTRL = 1.
7. Enable required outputs, DACs and mixers.
8. Enable VMID with required charge time e.g. VMIDSEL=01.
9. Wait 10ms (based on register updates of 325µs)
10. Setup digital interface, input amplifiers, PLL, ADCs and DACs for desired operation.
11. Disable VMID independent current bias, POBCTRL = 0.
12. Wait 500ms 1
13. Unmute L/ROUT1 and set desired volume, e.g. for 0dB R52 and R53 = 0x139h.
14. Unmute L/ROUT2 and set desired volume, e.g. for 0dB R54 and R55 = 0x139h.
Power Down 2:
1. Disable Thermal shutdown, TSDEN = TSOPCTRL = 0
2. Disable VMIDSEL=00 and BIASEN=0
3. Wait for VMID to discharge 3
4. Power off registers R1, R2, R3 = 0x000h
5. Remove external power supplies
Notes:
1. Charging time constant is determined by impedance selected by VMIDSEL and the value of
decoupling capacitor connected to VMID pin.
2. It is possible to interrupt the power down sequence and power up to VMID before the allocated
VMID discharge time. This is done by following the power-up sequence omitting steps 4 to 8.
3. Discharge time constant is determined by the values of analogue output capacitors.
PP, Rev 3.4, October 2006
23
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
