NCS2566

http://onsemi.com

11

APPLICATIONS INFORMATION

The NCS2566 6−channel video filter driver has been

optimized for Standard and High Definition video

applications covering the requirements of the standards

Composite video (CVBS), S−Video, Component Video

(480i/525i, 576i/625i, 720p/1080i) and related (RGB). The

first 3−channels (SD1, SD2, SD3) are dedicated for

Standard Definition, CVBS and S−Video applications for

which the frequency bandwidth required does not exceed 8

MHz. The 3 other channels (SD/HD1, SD/HD2, SD/HD3)

have selectable filters (8 MHz and 34 MHz) for covering

either standard−definition−like video applications or High

Definition video applications. These frequencies are

selectable using the pin SD/HD. If the application requires,

the video driver outputs may also be disabled using the

SD EN or SD/HD EN required by the application the pins

SD EN or SD/HD EN.

In the regular mode of operation each channel provides an

internal voltage−to−voltage gain of 2 from input to output.

This effectively reduces the number of external components

required as compared to discrete approaches implemented

with stand−alone op amps. An internal level shifter is

employed shifting up the output voltage by adding an offset

of 200 mV. This prevents sync pulse clipping and allows

DC−coupled output to the 150

W video load. In addition the

channel. This allows rejection of aliases or unwanted

over−sampling effects produced by the video DAC.

Similary for DVD recorders which uses an ADC, this

anti−aliasing filter (reconstruction filter) will avoid picture

quality issues and will aide filtration of parasitic signals

caused by EMI interference.

A built−in diode−like clamp is used in the chip for each

channel to support the AC−coupled mode of operation. The

clamp is active when the input signal goes below 0 V.

The built−in clamp and level shifter allow the device to

operate in different configuration modes depending on the

DAC output signal level and the input common mode

voltage of the video driver. When the configuration is

DC−Coupled at the Inputs and Outputs the 0.1

mF and

220

mF coupling capacitors are no longer used and the

clamps are in that case inactive; this configuration provides

a low cost solution which can be implemented with few

external components.

The input is AC−coupled when either the input−signal

amplitude goes over the range 0 V to 1.4 V or if the video

source requires such a coupling. In some circumstances it

may be necessary to auto−bias signals with the addition of

a pull−up and pull−down resistors or only pull−up resistor

(Typical 7.5 M

W combined with the internal 800 kW

pulldown) making the clamp inactive.

The output AC−coupling configuration is advantageous

for eliminating DC ground loop, but may have the drawback

of increasing sensitivity to video line or field tilt issues if the

output coupling capacitor is too small. DC ground loop with

the drawback of making the device more sensitive to video

line or field tilt issues in the case of a too low output coupling

capacitor. In some cases it may be necessary to increase the

nominal 220

mF capacitor value.

All the device pins are protected against electrostatic

discharge at a level of 4 kV HBM and 8 kV according to

IEC61000−4−2. This feature has been considered with a

particular attention with ESD structure able to sustain the

typical values requested by the systems like Set Top Boxes

or Blue-Ray players. This parameter is particularly

important for video driver which usually constitutes the last

stage in the video chain before the video output connector.

The IEC61000-4-2 standard has been used to test our

devices in the real application environment. Test

methodology can be provided on request.