LT6553

10

6553f

A fourth signal trace is provided at the bottom of the

DC714 demo board with dimensions identical to the

combined input and output of the other channels. This

trace can be used for calibrating the effects of electrical

delay and impedance mismatching and is not necessary

in an end-user application. Several jumpers and addi-

tional connectors are also included to allow for testing of

the enable feature and single supply operation.

Single Supply RGB Buffer Demo Board

The DC743A Demo Board uses the LT6553 in a single

supply application with AC coupled inputs and outputs. It

is nearly identical to the DC714 RGB Buffer Demo Board

but has the additional components required for AC cou-

pling and setting a DC bias point at the input. A schematic

of a single channel is shown in Figure 2. AC performance

of the LT6553 in the single supply application as shown is

nearly identical to performance with dual supplies.

The 6.8k and 2.2k bias resistors at the input set up a

nominal DC voltage at the input that keeps a video signal

within the input and output common mode range of the

part. On a 9V single supply, the input would sit at 2.2V DC,

and the output would sit at 4.4V.

Due to the 220

µF coupling cap at the output, the only

additional power dissipation due to the positive output

voltage is through the feedback and gain resistors. Since

those resistors are approximately 740

Ω in series, the

additional quiescent current is only 6mA per channel.

RGB Video Selector/Cable Driver

A video multiplexer can be implemented using the EN pins

of parallel LT6553s as shown in Figure 3. In this applica-

tion, all outputs are connected together and one LT6553 is

switched on while the other is switched off. A fast inverter

provides a complementary signal to ensure that only one

set of R, G and B channels is buffered at any time. As

shown, the outputs are connected before the 75

Ω series

termination resistors in order to reduce any DC attenua-

tion that may result from the non-infinite output imped-

ance of the disabled LT6553.

TYPICAL APPLICATIO S

Figure 2. Single Supply Configuration, One Channel Shown

7V TO 12V

80.6

Ω

75

Ω

75

Ω

1/3 LT6553

OUT

IN

6.8k

22

µF*

220

µF**

INPUT

2.2k

6553 F02

*

**

AVX 12066D226MAT

SANYO 6TPB220ML

AGND