WM8976 datasheet(46/83 Pages) WOLFSON

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WM8976

Preliminary Technical Data

PTD Rev 2.0 February 2005

LMIXEN

Left output channel mixer enable:

0 = disabled

1= enabled

Power

management

RMIXEN

Right output channel mixer enable:

0 = disabled

1 = enabled

Table 33 Left and Right Output Mixer Control

HEADPHONE OUTPUTS (LOUT1 AND ROUT1)

The headphone outputs, LOUT1 and ROUT1 can drive a 16

Ω or 32Ω headphone load, either

through DC blocking capacitors, or DC coupled without any capacitor. Each headphone output has

an analogue volume control PGA with a gain range of -57dB to +6dB as shown in Figure 22.

Figure 20 Headphone Outputs LOUT1 and ROUT1

Headphone Output using DC blocking capacitors:

DC Coupled Headphone Output:

Figure 21 Recommended Headphone Output Configurations

When DC blocking capacitors are used, then their capacitance and the load resistance together

determine the lower cut-off frequency, fc. Increasing the capacitance lowers fc, improving the bass

response. Smaller capacitance values will diminish the bass response. Assuming a 16

Ω load and

C1, C2 = 220

µF:

fc = 1 / 2

π RLC1 = 1 / (2π x 16Ω x 220µF) = 45 Hz

In the DC coupled configuration, the headphone “ground” is connected to the VMID pin. The VMID

pin can be configured as a DC output driver by setting the OUT3MUTE register bit. The DC voltage

on VMID in this configuration is equal to the DC offset on the LOUT1 and ROUT1 pins therefore no

DC blocking capacitors are required. This saves space and material cost in portable applications.

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