WM9713 datasheet(103/111 Pages) WOLFSON

103 / 111 page

Preliminary Technical Data

WM9713L

PTD, March 2004, Rev 2.2

103

AC-COUPLED HEADPHONE OUTPUT

The circuit diagram below shows how to connect a stereo headphone to the WM9713L.

Figure 35 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 16

Ω load and C1 = 220µF:

fc = 1 / 2

π 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 220

µF DC

blocking capacitors. This can be achieved by using OUT3 as a headphone pseudo-ground, as shown

below.

Figure 36 Capless Headphone Output Circuit Diagram

As the OUT3 pin produces a DC voltage of AVDD/2, there is no DC offset between HPL/HPR and

OUT3, and therefore no DC blocking capacitors are required. However, this configuration has some

drawbacks:

The power consumption of the WM9713L 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 WM9713L, the audio signal will not be transmitted properly.

OUT3 cannot be used for another purpose

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