WM8980CGEFLSLASHV datasheet(70/123 Pages) WOLFSON

70 / 123 page

WM8980

Pre-Production

PP, Rev 3.8, May 2012

L/ROUT2EN/

OUT3/4EN

OUT3BOOST/

OUT4BOOST/

SPKBOOST

VROI

OUTPUT CONFIGURATION

1kΩ tie-off to AVDD/2

30kΩ tie-off to AVDD/2

1kΩ tie-off to 1.5xAVDD/2

30kΩ tie-off to 1.5xAVDD/2

Output enabled (DC level=AVDD/2)

Output enabled (DC level=1.5xAVDD/2)

Table 53 Unused Output Pin Tie-off Options

VIDEO BUFFER

DESCRIPTION

The WM8980 incorporates a current mode output video buffer capable of operating from a 2.5V

supply, with an input 3

rd order Low Pass Filter (LPF) and clamp. The gain through this buffer can be

programmed as 0dB or 6dB (=6dB or 12dB unloaded) via the control interface. The current mode

output means that the signal swing seen at the output of the buffer will be the same as that at the

connection to the receiving equipment (e.g. a TV). Note that the input to the receiver should be AC

coupled and terminated to 75

, as is standard, for best performance.

Figure 36 Video Buffer

The input clamp should be enabled when using AC coupling at the input to the video buffer, using the

VBCLAMPEN register bit.

Note: The WM8980 Video Buffer input signal level at the input pin (VBIN) should not exceed 500mV

when using ac coupling or 330mV when using dc coupling when the input clamp circuit is enabled.

It is therefore recommended that the video signal is ac coupled into the video buffer and that the

video signal driving VBIN is disabled and is either high impedance or GND when the video buffer is

disabled.

Care should be taken with PCB layout, designing for at least 1GHz frequencies to avoid degrading

performance. Vias and sharp corners should be avoided and parasitic capacitance minimised on

signal paths, which should be kept as short and straight as possible. The VBVDD supply should be

decoupled as close to the pin as possible. See the “External Components” section for more

information.

LOW PASS FILTER

A low pass filter is integrated at the video buffer input, which is intended to remove images in the

video DAC output waveform at multiples of the DAC clock frequency. A 3

rd order Butterworth filter is

used, with the following characteristics:

WM8980CGEFL/V Datasheet(PDF) 70 Page - Wolfson Microelectronics plc

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