MAX4138 MAXIM [Maxim Integrated Products], MAX4138 Datasheet - Page 9

• Manufacturer Part Number: MAX4138
• Description: 1-Input/6-Output Video Distribution Amplifiers
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX4135/MAX4136 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 MAX4135/MAX4136 are capable of dri-
ving 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
Figure 2. MAX4136 Typical Operating Circuit
* TO TERMINATE TRANSMISSION LINE
_______________________________________________________________________________________
Driving Capacitive Loads
+5V
-5V
+5V
DC
DC
DC
0.1 F
75 *
75 *
75 *
75 *
75 *
75 *
0.1 F
0.1 F
Video Distribution Amplifiers
AGND
AGND
VCCO
VCCO
OUT4
OUT5
OUT6
OUT1
OUT3
OUT2
VEEO
VEEO
10
11
12
4
8
9
1
2
5
6
7
3
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
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 MAX4135/MAX4136 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).
MAX4136
SW1
SW2
SW3
SW4
SW5
SW6
IN
1-Input/6-Output
AGND
21
IN+
20
VEEI
19
RG
18
RF
17
VCCI
16
SEL4
15
SEL5
14
SEL6
13
SEL1
24
SEL2
23
SEL3
22
R
F
75 *
0.1 F
0.1 F
VIDEO
-5V
R
+5V
IN
G
DC
DC
9