WM9715L
Production Data
AC-COUPLED HEADPHONE OUTPUT
The circuit diagram below shows how to connect a stereo headphone to the WM9715L.
Figure 25 Simple Headphone Output Circuit Diagram
The DC blocking capacitors C1 and C2 together with the load resistance determine the lower cut-off
frequency, fc. Increasing the capacitance lowers fc, improving the bass response. Smaller
capacitance values will diminish the bass response. For example, with a 16Ω load and C1 = 220µF:
fc = 1 / 2π RLC1 = 1 / (2π x 16Ω x 220µF) = 45 Hz
DC COUPLED (CAPLESS) HEADPHONE OUTPUT
In the interest of saving board space and cost, it may be desirable to eliminate the 220µF DC
blocking capacitors. This can be achieved by using OUT3 as a headphone pseudo-ground, as shown
below.
Figure 26 Capless Headphone Output Circuit Diagram (OUT3SRC = 10)
As the OUT3 pin produces
a DC voltage of AVDD/2, there is no DC offset between
HPOUTL/HPOUTR and OUT3, and therefore no DC blocking capacitors are required. However, this
configuration has some drawbacks:
•
•
The power consumption of the WM9715L is increased, due to the additional power
consumed in the OUT3 output buffer.
If the DC coupled output is connected to the line-in of a grounded piece of equipment,
then OUT3 becomes short-circuited. Although the built-in short circuit protection will
prevent any damage to the WM9715L, the audio signal will not be transmitted properly.
•
OUT3 cannot be used for another purpose
PD Rev 4.0 December 2007
74
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
