NCS2564

http://onsemi.com

11

APPLICATIONS INFORMATION

The NCS2564 quad video 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 three SD/HD channels

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.

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 approached 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

This allows rejection of the aliases or unwanted

over-sampling effects produced by the video DAC.

Similarly for the case of DVD recorders which use an ADC,

this anti−aliasing filter (reconstruction filter) will avoid

picture quality issue and will aide filtration of parasitic

signals caused by EMI interference.

Figure 22. AC−Coupled Configuration at the Input and Output

0.1 mF

VCC

SD/HD

3

2

114

13

12

CVBS_IN

GND

GND

CVBS_OUT

6

7

411

8

9

SD/HD_EN

5

10

TV

220 mF

75 W

75 W

220 mF

220 mF

75 W

75 W

75 W

75 W

Rs

Y / G

Pb / B

Pr / R

CVBS

Y / G

Pb / B

Pr / R

SD/HD EN

CVBS EN

SD/HD SEL

75 W Cable

75 W Cable

75 W Cable

220 mF

75 W

75 W

CVBS

75 W Cable

0.1 mF

10 mF

+ 5 V

CVBS_EN

SD/HD IN1

SD/HD IN2

SD/HD IN3

SD/HD OUT1

SD/HD OUT2

SD/HD OUT3

Rs

Rs

Rs

0.1 mF

0.1 mF

0.1 mF

A built−in diode−like clamp is used into 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 (Figure 23).

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

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

source requires such a coupling. In some circumstances it

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

a pullup and pulldown resistors or only pullup 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 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.

Shutdown Mode

If the enable pins are left open by default the circuit will

be enabled. The Enable pin offers a shutdown function, so

the NCS2564 can consequently be disabled when not used.

The NCS2564’s quiescent current reduces to 42

mA typical

during shutdown mode.

DC−Coupled Output

The outputs of the NCS2564 can be DC−coupled to a

150

W load (Figure 23). This has the advantage of

eliminating the AC−coupling capacitors at the output by

reducing the number of external components and saving

space on the board. This can be a key advantage for some

applications with limited space.

The problems of field tilt effects on the video signal are

also eliminated providing the best video quality with

optimal dynamic or peak−to−peak amplitude of the video

signal allowing operating thanks to the built−in level shifter

without risk of signal clipping. In this coupling

configuration the average output voltage is higher than 0 V

and the power consumption can be a little higher than with

an AC−coupled configuration.