WM8955BLGECOSLASHV datasheet(42/44 Pages) WOLFSON

42 / 44 page

WM8955BL

Production Data

PD Rev 4.1 February 2007

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 any capacitor.

Headphone Output using DC blocking capacitors

DC Coupled Headphone Output

(OUT3SW = 00)

Figure 30 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

= 220

μF:

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

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

be enabled by setting OUT3 = 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 only to headphones, and not to the

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

the headphone outputs, such a connection may be noisy, and may not function properly if the other

device is grounded.

EARPIECE OUTPUT CONFIGURATION

LOUT2 and ROUT2 can differentially drive a mono 32

Ω earpiece as shown below.

Figure 31 Earpiece Output Connection

The right channel is inverted by setting the ROUT2INV bit, so that the signal across the earpiece is

the sum of left and right channels.

LOUT2

ROUT2

WM8955BL

ROUT2INV = 1

OUT

= L-(-R) = L+R

-1

LEFT

MIXER

RIGHT

MIXER

ROUT2VOL

LOUT2VOL

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