WM8976 datasheet(18/83 Pages) WOLFSON

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WM8976

Preliminary Technical Data

PTD Rev 2.0 February 2005

RECOMMENDED POWER UP/DOWN SEQUENCE

In order to minimise output pop and click noise, it is recommended that the WM8976 device is

powered up and down using one of the following sequences:

Power Up When NOT Using the Output 1.5x Boost Stage:

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

Set BIASEN = 1, BUFIOEN = 1 and also the VMIDSEL[1:0] bits in the Power Management

1 register. R1 = 0x00D. *Refer notes 1 and 2.

Wait for the VMID supply to settle. *Refer note 2.

Set VROI = 1. R49 = 0x003.

Set L/ROUT1EN = 1. R1 = 0x180.

Set L/RMIXEN and DACEN = 1. R3 = 0x00F.

Enable other mixers as required.

Enable other outputs as required.

Power Up When Using the Output 1.5x Boost Stage:

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

Set BIASEN = 1, BUFIOEN = 1, BUFDCOPEN = 1 and also the VMIDSEL[1:0] bits in the

Power Management 1 register. R1 = 0x10D. *Refer notes 1 and 2.

Wait for the VMID supply to settle. *Refer note 2.

Set VROI = 1 and SPKBOOST = 1. R49 = 0x007.

Set L/ROUT2EN = 1, L/RMIXEN = 1 and DACEN = 1. R3 = 0x06F. *Note 3.

Enable other mixers as required.

Enable other outputs as required.

Power Down (all cases):

Disable power management register 1 by setting R1[8:0]=0x00.

Disable all other output stages.

Remove external power supplies.

Notes:

This step enables the internal device bias buffer and the VMID buffer for unassigned

inputs/outputs. This will provide a startup reference voltage for all inputs and outputs. This will

cause the inputs and outputs to ramp towards VMID (NOT using output 1.5x boost) or 1.5 x

(AVDD/2) (using output 1.5x boost) in a way that is controlled and predictable (see note 2).

Choose the value of the VMIDSEL bits based on the startup time (VMIDSEL=10 for slowest

startup, VMIDSEL=11 for fastest startup). Startup time is defined by the value of the VMIDSEL

bits (the reference impedance) and the external decoupling capacitor on VMID.

Setting DACEN to off while operating in x1.5 boost mode will cause the VMID voltage to drop to

AVDD/2 midrail level and cause an output pop. To avoid this de-select DAC from mixer inputs

before disabling the DAC.

In addition to the power on sequence, it is recommended that the zero cross functions are used

when changing the volume in the PGAs to avoid any audible pops or clicks.

WM8976 Datasheet(PDF) 18 Page - Wolfson Microelectronics plc

WM8976 Datasheet(HTML) 18 Page - Wolfson Microelectronics plc

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