MAX4029 Maxim, MAX4029 Datasheet - Page 9

• Manufacturer Part Number: MAX4029
• Description: The MAX4028/MAX4029 are 5V, triple/quad, 2:1 voltage-feedback multiplexer-amplifiers with input clamps and a fixed gain of +2V/V (6dB)
• Manufacturer: Maxim

Table 2. MAX4029 Clamp Settings for Video Formats
R, G, B have sync on none.
The MAX4028/MAX4029 have a fixed gain of +2V/V that
is internally set with two 1kΩ thin-film resistors. The
impedance of the internal feedback resistors must be
taken into account when operating multiple MAX4028/
MAX4029s in large multiplexer applications.
The MAX4028/MAX4029 are well suited to drive coaxial
transmission lines when the cable is terminated at both
ends, as shown in Figure 3, where the fixed gain of
+2V/V compensates for the loss in the resistors, R
A correctly terminated transmission line is purely resis-
tive and presents no capacitive load to the amplifier.
Reactive loads decrease phase margin and may pro-
duce excessive ringing and oscillation.
Another concern when driving capacitive loads is the
amplifier’s output impedance, which appears inductive
at high frequencies. This inductance forms an L-C reso-
INPUT
INPUT
INPUT
1
2
3
4
1
2
3
4
1
2
3
4
Applications Information
Multiplexer-Amplifiers with Input Clamps
_______________________________________________________________________________________
FORMAT
FORMAT
FORMAT
H-Sync
Cvbs1
Cvbs2
Cvbs3
Cvbs4
Cvbs
Cvbs
Driving Capacitive Loads
G
C
B
R
Y
Video Line Driver
CLAMP/KEY
CLAMP/KEY
CLAMP/KEY
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Key
Key
Key
Key
T
.
nant circuit with the capacitive load, which causes
peaking in the frequency response and degrades the
amplifier’s phase margin.
Figure 3. Video Line Driver
75Ω CABLE
75Ω CABLE
Triple/Quad, 2:1 Video
R
KEYREF
75Ω
75Ω
R
R
Gs, B, R have sync only on Green.
R, G, B have sync on all.
T
T
0.1µF
0.1µF
INPUT
INPUT
INPUT
1
2
3
4
1
2
3
4
1
2
3
4
IN_A
IN_B
A/B
CLAMP
MAX4028
MAX4029
DISABLE
FORMAT
FORMAT
FORMAT
Cvbs
Cvbs
Cvbs
OUT_
Gs
Pb
G’
Pr
B’
R’
R
B
Y
75Ω
R
T
75Ω CABLE
CLAMP/KEY
CLAMP/KEY
CLAMP/KEY
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Clamp
Key
Key
Key
Key
R
75Ω
T
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