wm9715l Wolfson Microelectronics plc, wm9715l Datasheet - Page 74

• Manufacturer Part Number: wm9715l
• Description: Ac?97 Audio And Touchpanel Codec
• Manufacturer: Wolfson Microelectronics plc

WM9715L
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AC-COUPLED HEADPHONE OUTPUT
DC COUPLED (CAPLESS) 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 R
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:
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•
•
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
L
C
1
= 1 / (2π x 16Ω x 220µF) = 45 Hz
PD Rev 4.0 December 2007
Production Data
74