Production Data
WM8978
w
PD, Rev 4.5, October 2011
83
In 2-wire mode the WM8978 has a fixed device address, 0011010.
RESETTING THE CHIP
The WM8978 can be reset by performing a write of any value to the software reset register (address
0 hex). This will cause all register values to be reset to their default values. In addition to this there
is a Power-On Reset (POR) circuit which ensures that the registers are set to default when the device
is powered up.
POWER SUPPLIES
The WM8978 can use up to five separate power supplies:
AVDD and AGND: Analogue supply, powers all analogue functions except the speaker output and
mono output drivers. AVDD can range from 2.5V to 3.6V and has the most significant impact on
overall power consumption (except for power consumed in the headphone). A large AVDD slightly
improves audio quality.
SPKVDD and SPKGND: Headphone and Speaker supplies, power the speaker and mono output
drivers. SPKVDD can range from 2.5V to 5V. SPKVDD can be tied to AVDD, but it requires separate
layout and decoupling capacitors to curb harmonic distortion. With a larger SPKVDD, louder
headphone and speaker outputs can be achieved with lower distortion. If SPKVDD is lower than
AVDD, the output signal may be clipped.
DCVDD: Digital core supply, powers all digital functions except the audio and control interfaces.
DCVDD can range from 1.71V to 3.6V, and has no effect on audio quality. The return path for
DCVDD is DGND, which is shared with DBVDD.
DBVDD can range from 1.71V to 3.6V. DBVDD return path is through DGND.
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.
DCVDD should be greater than or equal to 1.9V when using the PLL.
RECOMMENDED POWER UP/DOWN SEQUENCE
In order to minimise output pop and click noise, it is recommended that the WM8978 device is
powered up and down using one of the following sequences:
Power-up when NOT using the output 1.5x boost stage:
1.
Turn on external power supplies. Wait for supply voltage to settle.
2.
Mute all analogue outputs.
3.
Set L/RMIXEN = 1 and DACENL/R = 1 in register R3.
4.
Set BUFIOEN = 1 and VMIDSEL[1:0] to required value in register R1. Wait for the VMID supply
to settle. *Refer notes 1 and 2.
5.
Set BIASEN = 1 in register R1.
6.
Set L/ROUT1EN = 1 in register R2.
7.
Enable other mixers as required.
8.
Enable other outputs as required.
9.
Set remaining registers.
Summary of Contents for WM8978
Page 11: ...Production Data WM8978 w PD Rev 4 5 October 2011 11 SPEAKER OUTPUT THD VERSUS POWER...
Page 14: ...WM8978 Production Data w PD Rev 4 5 October 2011 14 AUDIO PATHS OVERVIEW...
Page 55: ...Production Data WM8978 w PD Rev 4 5 October 2011 55 Figure 26 Left Right Output Channel Mixers...
Page 60: ...WM8978 Production Data w PD Rev 4 5 October 2011 60 Figure 29 Speaker Outputs LOUT2 and ROUT2...