WM8955BL
Production Data
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 any capacitor.
DC Coupled Headphone Output
Headphone Output using DC blocking capacitors
(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 16Ω 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 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 32Ω earpiece as shown below.
LEFT
MIXER
LOUT2
WM8955BL
ROUT2INV = 1
LOUT2VOL
V
= L-(-R) = L+R
OUT
-1
ROUT2
RIGHT
MIXER
ROUT2VOL
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.
PD Rev 4.1 February 2007
42
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
