WM8955L
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HEADPHONE OUTPUT CONFIGURATION
The analogue outputs LOUT1/ROUT1, LOUT2/ROUT2, and OUT3 can drive a 16Ω or 32Ω
headphone load, either through DC blocking capacitors, or DC coupled without anycapacitor.
DC Coupled Headphone Output
Headphone Output using DC blocking capacitors
(OUT3SW = 00)
C1 220uF
LOUT1
LOUT1
ROUT1
WM8955L
HPDCEN = 1
WM8955L
C2 220uF
HPGND = 0V
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 = 220µF:
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 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.
LEFT
MIXER
LOUT2
LOUT2VOL
WM8955L
ROUT2INV = 1
VSPKR = L-(-R) = L+R
-1
ROUT2
RIGHT
MIXER
ROUT2VOL
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.
Product Preview Rev 0.4 May2003
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
