MAX4138(1996) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX4138 Datasheet PDF : 12 Pages
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1-Input/4-Output
Video Distribution Amplifiers
+5VDC
-5VDC
+5VDC
* TO TERMINATE TRANSMISSION LINE
0.1µF
N.C.
1
VCCO
2
75Ω*
OUT1
3
75Ω*
AGND
4
OUT2
5
VEEO
6
VEEO
0.1µF
7
75Ω*
OUT3
8
AGND
9
75Ω*
0.1µF
OUT4
10
VCCO
11
N.C.
12
MAX4138
SW1
OUT1
SW2
OUT2
IN
OUT3
OUT4
SW3
SW4
N.C.
24
SEL1
23
SEL2
22
AGND
21
IN+
20
VIDEO
IN
75Ω*
VEEI
19
RG
18
RF
RF
17
VCCI
16
SEL3
15
SEL4
14
N.C.
13
-5VDC
0.1µF
RG
+5VDC
0.1µF
Figure 2. MAX4138 Typical Operating Circuit
Driving Capacitive Loads
The MAX4137/MAX4138 provide maximum AC perfor-
mance with no output load capacitance. This is the
case when they are driving a correctly terminated trans-
mission line (i.e., a back-terminated 75Ω cable).
However, the MAX4137/MAX4138 are capable of
driving capacitive loads up to 10pF without oscillations,
but with reduced AC performance.
Driving large capacitive loads increases the chance of
oscillations in most amplifier circuits. This is especially
true for circuits with high loop gain, such as voltage fol-
lowers. The amplifier’s output resistance and the load
capacitor combine to add a pole and excess phase to
the loop response. If the frequency of this pole is low
enough and phase margin is degraded sufficiently,
oscillations may occur.
A second problem when driving capacitive loads
results from the amplifier’s output impedance, which
looks 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 gain margin.
The MAX4137/MAX4138 drive capacitive loads up to
10pF without oscillation. However, some peaking (in the
frequency domain) or ringing (in the time domain) may
occur (Figure 3).
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