ADV476

REV. B

–8–

Figure 5. RGB Video Output Waveform

Table V. Video Output Truth Table

RED, GREEN,

DAC

Description

BLANK

Input Data

WHITE LEVEL

19.05

1

FFH

VIDEO

Video

1

DATA

BLACK LEVEL

0

1

00H

BLANK LEVEL

0

0

xxH

NOTE

Reference Input

The ADV476 requires an active current reference to enable the

DACs provide stable and accurate video output levels. The rela-

tionship between the output voltage and the required input ref-

erence current is given by:

I

VO ( FULL SCALE )

2.15

× R

L

where

Ω

(for doubly terminated 75

Ω load)

= 75

Ω

(for singly terminated 75

Ω load)

and

VO = 0.714 V (RS-343A video levels)

= 1.0 V

(RS-170 video levels).

In a standard application which requires RS-343A video levels

to be driven into a doubly terminated 75

Ω load (R

Ω),

the necessary reference input current is:

To drive the same levels into a singly terminated 75

Ω load

Ω), the reference current is:

A suggested current reference design for the doubly terminated

case, with RS-343A video levels and based on the LM334, a

three-terminal adjustable current source, is shown in Figure 6.

Figure 6. Current Reference Design Using an LM334

Current Source