LT6554CGNTR Linear Technology, LT6554CGNTR Datasheet - Page 10

• Manufacturer Part Number: LT6554CGNTR
• Manufacturer: Linear Technology

Specifications of LT6554CGNTR

• Lead Free Status / RoHS Status: Not Compliant

LT6554
TYPICAL APPLICATIO
RGB Buffer Demo Board
The DC794 Demo Board illustrates optimal routing,
bypassing and termination using the LT6554 as an
RGB video buffer. The schematic is shown in Figure 4. All
inputs and outputs are routed to have a characteristic
impedance of 75Ω. The 75Ω input shunt and output series
terminations are connected as close to the part as pos-
sible. While the 75Ω back termination resistors at the
outputs of the LT6554 minimize signal reflections in the
output traces and isolate the part from any capacitive
loading in those traces, they also contribute to gain error
if the output is not terminated with high impedance. For
example, if the output is terminated with a 1k load, the 75Ω
back termination will cause a 7% gain error. Decreasing
the value of the back termination resistors will decrease
the signal attenuation but may compromise the AC re-
sponse. However, connecting the LT6554 outputs to the
output traces on the DC794 board without some series
resistance is not recommended; 10Ω to 20Ω is generally
sufficient.
A fourth signal trace is provided at the bottom of the
DC794 demo board with dimensions identical to the
10
CAL
INR
ING
INB
AGND
5
4
3
2
5
4
3
2
5
4
3
2
5
4
3
2
EN
50Ω BNC
5 4 3 2
BANANA
BNC × 3
JACK
BNC
1
J1
J5
J6
J7
J3
J8
1
1
1
1
AGND
Z = 75
Z = 75
Z = 75
E3
AGND
1 2
SINGLE
DGND
JP2
1
SUPPLY
FLOAT
R4
75Ω
JP3
3
2
DUAL
3
R5
75Ω
DGND
EN
E1
E2
U
ENABLE
1 2
R6
75Ω
CONTROL
C5
470pF
JP1
EXT
Figure 4. DC794 Demo Board Schematic
3
C6
1000pF
1
2
3
4
5
6
7
8
EN
DGND
INR
AGND
ING
AGND
INB
V
–
C7
470pF
LT6554
OUTR
OUTG
OUTB
V
V
V
V
V
C8
4700pF
+
+
–
+
–
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. Jumpers and additional con-
nectors are also included to allow for evaluation of the
enable feature and single supply operation.
RGB Video Selector/Cable Driver
A video multiplexer can be implemented using the EN pins
of parallel LT6554s as shown in Figure 5. In this applica-
tion, the corresponding outputs are connected together
and one LT6554 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.
Since the output impedance of a disabled LT6554 is very
high, adding additional channels will not resistively load
an enabled output. However, since the disabled LT6554
has around 6pF of capacitance, it may be desirable to
resistively isolate the outputs of each channel to maintain
flat frequency response as shown in the graph labeled
“Maximum Capacitive Load vs Output Series Resistor” in
the Typical Performance Characteristics section.
16
15
14
13
12
11
10
9
C9
10µF, 16V
1210
C1
4700pF
75Ω
75Ω
75Ω
R1
R2
R3
C2
470pF
ALL BNC: CANARE BCJ-BPLH
Z = 75
Z = 75
Z = 75
Z = 75
C3
4700pF
C4
10µF, 16V
1210
V
V
BANANA JACK
+
–
BANANA
1
1
1
1
BNC x3
JACK
BNC
J10
J11
J12
J2
J9
J4
V
V
+
–
5
4
3
2
5
4
3
2
5
4
3
2
5
4
3
2
OUTR
OUTG
OUTB
CAL
6554 F04
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