WM9712L datasheet(73/77 Pages) WOLFSON

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Production Data

WM9712L

PD Rev 4.5 August 2006

AC-COUPLED HEADPHONE OUTPUT

The circuit diagram below shows how to connect a stereo headphone to the WM9712L.

C2 220uF

HPOUTL

HPOUTR

HPGND = 0V

C1 220uF

WM9712L

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 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.

WM9712L

HPOUTL

HPOUTR

OUT3 = AVDD/2

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 WM9712L 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 WM9712L, the audio signal will not be transmitted properly.

•

OUT3 cannot be used for another purpose

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