WM8955 datasheet(42/43 Pages) WOLFSON

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WM8955L

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Product Preview Rev 0.4 May2003

HEADPHONE OUTPUT CONFIGURATION

The analogue outputs LOUT1/ROUT1, LOUT2/ROUT2, and OUT3 can drive a 16

Ω or 32Ω

headphone load, either through DC blocking capacitors, or DC coupled without anycapacitor.

Headphone Output using DC blocking capacitors

DC Coupled Headphone Output

(OUT3SW = 00)

WM8955L

C2 220uF

LOUT1

ROUT1

HPGND=0V

C1 220uF

WM8955L

HPDCEN = 1

LOUT1

ROUT1

HPDC = AVDD/2

Figure 26 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 Ohm load and

C1 = 220

µF:

fc =1 /2

π RLC1 =1/ (2π x16Ω x 220µF) = 45 Hz

In the DC coupled configuration, the headphone “ground” is connected to the OUT3 pin, which must

be enabled bysetting O3 = 1 and OUT3SW = 00. As the OUT3 pin produces a DC voltage of

AVDD/2 (=VREF), there is no DC offset between LOUT1/ROUT1 and OUT3, and therefore no DC

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

It is recommended to connect the DC coupled headphone outputs onlyto headphones, and not to

the line input of another device. Although the built-in short circuit protection will prevent anydamage

to the headphone outputs, such a connection maybe noisy, and maynot function properlyif the

other device is grounded.

SPEAKER OUTPUT CONFIGURATION

LOUT2 and ROUT2 can differentiallydrive a mono 8

Ω speaker as shown below.

LOUT2

ROUT2

WM8955L

ROUT2INV = 1

SPKR = L-(-R) = L+R

-1

LEFT

MIXER

RIGHT

MIXER

ROUT2VOL

LOUT2VOL

Figure 27 Speaker Output Connection

The right channel is inverted bysetting the ROUT2INV bit, so that the signal across the loudspeaker

is the sum of left and right channels.

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