MAX4028 データシートの表示（PDF） - Maxim Integrated
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MAX4028 Datasheet PDF : 12 Pages
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MAX4028/MAX4029
Triple/Quad, 2:1 Video
Multiplexer-Amplifiers with Input Clamps
Table 2. MAX4029 Clamp Settings for Video Formats
INPUT
FORMAT
CLAMP/KEY
INPUT
FORMAT
1
Cvbs1
Clamp
1
Gs
2
Cvbs2
Clamp
2
R
3
Cvbs3
Clamp
3
B
4
Cvbs4
Clamp
4
Cvbs
Gs, B, R have sync only on Green.
INPUT
FORMAT
1
H-Sync
2
G
3
B
4
R
R, G, B have sync on none.
CLAMP/KEY
Clamp
Key
Key
Key
INPUT
1
2
3
4
FORMAT
Y
Pr
Pb
Cvbs
INPUT
1
2
3
4
FORMAT
Y
C
Cvbs
Cvbs
CLAMP/KEY
Clamp
Key
Clamp
Clamp
INPUT
FORMAT
1
Cvbs
2
G’
3
B’
4
R’
R, G, B have sync on all.
CLAMP/KEY
Clamp
Key
Key
Clamp
CLAMP/KEY
Clamp
Key
Key
Clamp
CLAMP/KEY
Clamp
Clamp
Clamp
Clamp
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.
Applications Information
Video Line Driver
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, RT.
Driving Capacitive Loads
A correctly terminated transmission line is purely
resistive and presents no capacitive load to the amplifier.
Reactive loads decrease phase margin and may produce
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
resonant circuit with the capacitive load, which causes
peaking in the frequency response and degrades the
amplifier’s phase margin.
A/B
75Ω CABLE 0.1F
IN_A
RT
75Ω
75Ω CABLE 0.1F
IN_B
DISABLE
RT
OUT_ 75Ω
75Ω CABLE
RT
75Ω
RT
75Ω
CLAMP
RKEYREF
MAX4028
MAX4029
Figure 3. Video Line Driver
Although the MAX4028/MAX4029 are optimized for AC
performance and are not designed to drive highly capaci-
tive loads, they are capable of driving up to 15pF without
oscillations. However, some peaking may occur in the fre-
quency domain (Figure 4). To drive larger capacitive loads
or to reduce ringing, add an isolation resistor between the
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