MAX465 MAXIM [Maxim Integrated Products], MAX465 Datasheet - Page 9

• Manufacturer Part Number: MAX465
• Description: Two-Channel, Triple/Quad RGB Video Switches and Buffers
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 2. Differential Phase and Gain Error Test Circuits (a) for the MAX469/MAX470 Gain-of-Two Amplifiers, (b) for the
MAX467/MAX468 Unity-Gain Amplifiers
High-speed performance, excellent output current
capability, and an internally fixed gain of two make the
MAX465/MAX466/MAX469/MAX470 ideal for driving
50Ω or 75Ω back-terminated coaxial cables. The
MAX465/MAX466/MAX469/MAX470 will drive a 150Ω
load (75Ω back-terminated cable) to ±2.5V.
The Typical Operating Circuit shows the MAX465/MAX466
driving four back-terminated 75Ω video cables. The
back-termination resistor (at each amplifier output) pro-
vides impedance matching at the driven end of the
cable to eliminate signal reflections. It forms a voltage
divider with the load impedance, which attenuates the
signal at the cable output by one-half. The amplifier
operates with an internal 2V/V closed-loop gain to pro-
vide unity gain at the cable’s output.
Driving large capacitive loads increases the likelihood
of oscillation in most amplifier circuits. This is especially
true for circuits with high loop-gains, like voltage follow-
ers. The amplifier’s output impedance and the capaci-
tive load form an RC filter that adds a pole to the loop
response. If the pole frequency is low enough, as
when driving a large capacitive load, the circuit phase
margin is degraded and oscillation may occur.
(a)
(b)
SOURCE:
TEKTRONIX
1910 DIGITAL GENERATOR
75
75
_______________________________________________________________________________________
75 CABLE
Driving Capacitive Loads
75 CABLE
Driving Coaxial Cable
RGB Video Switches and Buffers
DUT
MAX467/MAX468
DUT
150
MAX469/MAX470
Two-Channel, Triple/Quad
75
75 CABLE
The MAX463–MAX470 phase margin and capacitive-
load driving performance are optimized by internal
compensation. When driving capacitive loads greater
than 50pF, connect an isolation resistor between the
amplifier output and the capacitive load, as shown in
Figure 3.
Figure 3a. Using an Isolation Resistor with a Capacitive Load
A
V
= 2
IN_
75 CABLE
75
MAX468
A
75 CABLE
V
= 1
75
75
MEASUREMENT:
TEKTRONIX VM700
VIDEO MEASUREMENT
SET
OUT_
12
75
100pF
9