MAX4024 Maxim, MAX4024 Datasheet - Page 15

• Manufacturer Part Number: MAX4024
• Description: The MAX4023–MAX4026 family of voltage feedback multiplexer-amplifiers combine low-glitch switching and excellent video specifications with fixed or settable gain
• Manufacturer: Maxim

Figure 1. MAX4023/MAX4025 Noninverting Gain Configuration
sitic inductance, keep PC traces short and use surface-
mount components.
If input termination resistors and output back-termina-
tion resistors are used, they should be surface-mount
types, and should be placed as close to the IC pins as
possible.
The MAX4024/MAX4026 are well suited to drive short
coaxial transmission lines when the cable is terminated
at both ends (as shown in Figure 2a) where the fixed
gain of +2 compensates for the loss in the resistors.
The MAX4023/MAX4025 have settable gain to equalize
long cables. The MAX4023/MAX4025 allow adding
functions that normally require additional op amps. For
example, a cable driver can “boost” the high frequen-
cies for long runs, making the part perform multiple
functions. Figure 2b shows the “cable booster” using
the MAX4023/MAX4025.
A correctly terminated transmission line is purely resis-
tive and presents no capacitive load to the amplifier.
______________________________________________________________________________________
Amplifiers with Fixed and Settable Gain
Triple and Quad, 2:1 Video Multiplexer-
75Ω CABLE
75Ω CABLE
Driving Capacitive Loads
75Ω
75Ω
R
R
T
T
Video Line Driver
IN_A
IN_B
A/B
MAX4023
MAX4025
EN
OUT_
FB_
Reactive loads decrease phase margin and may pro-
duce excessive ringing and oscillation (see Typical
Operating Characteristics ).
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-
nant circuit with the capacitive load, which causes
peaking in the frequency response and degrades the
amplifier’s phase margin.
Although the MAX4023–MAX4026 are optimized for AC
performance and are not designed to drive highly
capacitive loads, they are capable of driving up to
33pF without oscillations. However, some peaking may
occur in the frequency domain (Figure 3). To drive larg-
er capacitive loads or to reduce ringing, add an isola-
tion resistor between the amplifier’s output and the load
(Figure 4). The value of R
gain and the capacitive load (Figure 5). Also note that
the isolation resistor forms a divider that decreases the
voltage delivered to the load.
R
R
F
G
75Ω
R
T
75Ω CABLE
ISO
R
75Ω
T
depends on the circuit’s
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