ML6429

8

TYPICAL APPLICATIONS

BASIC APPLICATIONS

The ML6429 provides channels for two banks of inputs for

RGB and composite video. The R and G channels can be

used as luma inputs while the B channel can be used as a

chroma input. Composite outputs and an H-sync output is

also provided. There are several configurations available

with the ML6429. Figure 4 includes a list of basic output

options for composite, S-video, TV modulator, and RGB

outputs. Note that each composite channel can drive a CV

load or a channel modulator simultaneously. The ML6429

standalone can be used as an EVC or SCART cable driver

with nine video sources (75

W or low impedance buffer)

and seven video outputs. All inputs and outputs are AC

coupled. When driving seven loads, power dissipation

must be measured to ensure that the junction temperature

doesn't exceed 120ºC.

EVC CABLE DRIVING

The ML6429 can be configured to drive composite video,

S-video, and horizontal sync through an EVC connector

(Figure 5). Composite video and S-video inputs are filtered

internal 75

W cable drivers. A buffered H-sync output is

also available.

SCART CABLE DRIVING

The ML6429 can be configured either as a SCART cable

driver (Figure 4) or as a SCART cable driver and S-video

driver (Figure 6). A horizontal sync output is also available.

Note that the ML6429 can be used in a master-slave mode

where the sync-out from the master is used as the sync-in

of the slave; this allows the CV, S-video, and RGB channels

to operate under the same sync signals.

Note that in SCART applications, it is not always necessary

to AC couple the outputs. Systems using SCART

connectors for RGB and composite video can typically

handle between 0 and 2V DC offset (see DC Coupled

Applications section).

RGB APPLICATIONS

RGB video can be filtered and driven through the

ML6429. For sync suppressed RGB, the sync signal can be

derived from SYNCIN PIN.

OSD (ON-SCREEN DISPLAY) APPLICATIONS

Unfiltered RGB video from an OSD processor needs to be

filtered and then synchronized to a fast blanking interval

or alpha-key signal for later video processing. With the

total filter delay being 80ns ±10ns, a D flip-flop or similar

delay element can be used to delay the fast blanking

interval or alpha-key signal, which synchronizes the RGB

and OSD signals (Figure 9).

CHANNEL MULTIPLEXING

The ML6429 can be configured for multiple composite

channel multiplexing (Figure 8). Composite and RGB

sources such as VCRs, and digital MPEG 2 sources can be

selected using the ML6429 swap mux controls. A/B MUX,

SWAP CVU, and SWAP CVF signals can be used to select

and route from various input sources.

DC COUPLED APPLICATIONS

The 220µF capacitor coupled with the 150

W termination

forms a highpass filter which blocks the DC while passing

the video frequencies and avoiding tilt. Lower values such

as 10µF would create a problem. By AC coupling, the

average DC level is zero. Thus, the output voltages of all

channels will be centered around zero.

Alternately, DC coupling the output of the ML6429 is

allowable. There are several tradeoffs: The average DC

level on the outputs will be 2V; Each output will dissipate

an additional 40mW nominally; The application will need

to accommodate a 1V DC offset sync tip; And it is

recommended to limit one 75

W load per output. However,

if two loads are required to be driven at a time on the

composite output while DC coupling is used, then the

drivers. Thus, the composite load driving requirement is

divided into two line drivers versus one.

Required Setup: A composite or luma or green signal must

necessary sync signals to other channels (R,G,B,Y,C).

Otherwise, sync must be provided at the SYNCIN pin. For

RGB applications, the green channel with sync can be

USING THE ML6429 FOR PAL APPLICATIONS

The ML6429 can be optimized for PAL video by adding

frequency peaking to the composite and S-video outputs.

Figure 10 illustrates the use of a additional external

capacitor (300pF), added in parallel to the output source

termination resistor. This raises the frequency response

from 1.0dB down at 4.8MHz (for no peaking cap) to 0.2dB

down at 4.8MHz (for 300 pF), which allows for accurate

reproduction of the upper sideband of the PAL subcarrier.

Figure 11 shows the frequency response of PAL video with

various values of peaking capacitors (0pF, 220pF, 270pF,

300pF) between 0 and 10MHz.

For NTSC applications without the peaking capacitor, the

rejection at 27MHz is 40dB (typical). For PAL applications

with the peaking capacitor, the rejection at 27MHz is

34dB (typical). (Figure 12). The differential group delay is

shown in Figure 13 with and without a peaking capacitor

(0pF, 220pF, 270pF, and 300pF) varies slightly with

capacitance; from 8ns to 13ns.