WM8750 datasheet(36/60 Pages) WOLFSON

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WM8750BL

Production Data

PD, Rev 4.1, August 2012

HEADPHONE OUTPUT

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

 or 32 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 13 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, C2 = 220

F:

fc = 1 / 2 RLC1 = 1 / (2 x 16 x 220F) = 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 thermal shutdown circuit 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.

SPEAKER OUTPUT

LOUT2 and ROUT2 can differentially drive a mono 8

 speaker as shown below.

Figure 14 Speaker Output Connection

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

is the sum of left and right channels.

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