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 220µF 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 740Ω 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 75Ω 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
U
Figure 2. Single Supply Configuration, One Channel Shown
+
7V TO 12V
80.6Ω
75Ω
75Ω
1/3 LT6553
OUTIN
6.8k
22µF*
220µF**
INPUT
2.2k
6553 F02
*
**
AVX 12066D226MAT
SANYO 6TPB220ML
AGND
