Datasheet
1
2
3
4
5
6
7
8
9
10
11
12
V
CC
R
EXT
GND
B
IN
R
IN
G
IN
INPUT SELECT
P
B IN
P
R IN
Y
H SYNC
IN
V SYNC
IN
H SYNC
OUT
V SYNC
OUT
POWER SAVE
SD/HD SELECT*
AUTO/MANUAL
DETECT SELECT
GND
V
CC
B
OUT
R
OUT
G
OUT
100 PF
100:
100:
SYNC on Y
GND
100 PF
100 PF
LMH6734
33:
33:
33:
75:
75:
75:
R
OUT
G
OUT
B
OUT
500:
500:
H SYNC
OUT
V SYNC
OUT
13
14
15
16
17
18
19
20
21
22
23
24
+++
10 k:
10 k:
10 k:
NEGATIVE
EDGE
SYNCs
POSITIVE EDGE SYNCs
LMH1251
www.ti.com
SNLS193J –AUGUST 2005–REVISED MARCH 2013
Figure 8. Simplified Application Diagram for Driving a VGA Cable
LAYOUT CONSIDERATIONS
The most important point to note regarding the layout of the LMH1251 on a PCB is that the trace length between
the output pins of the LMH1251 and the input AC coupling capacitors of the next stage ADC or preamplifier must
be as minimal as possible. The trace lengths of the H Sync and V Sync outputs should also be minimized, as the
capacitive loading on these outputs must not exceed 6 pF. For long signal paths leading up to the input of the
LMH1251, controlled impedance lines should be used, along with impedance matching elements. Bypass
capacitors should be placed as close as possible to the supply pins of the device. The larger electrolytic bypass
capacitor can be located farther from the device. The 10 kΩ external resistor should also be placed as close as
possible to the R
EXT
pin. All video signals must be kept away from the R
EXT
pin (15). This pin has a very high
input impedance and will pick up any high frequency signals routed near it.
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