Video Line Driver
The MAX4389/MAX4390/MAX4392–MAX4396 are low-
power, voltage-feedback amplifiers featuring large-signal
(2VP-P) bandwidths of 90MHz and 0.1dB large-signal
gain flatness of 24MHz. They are designed to mini-
mize differential-gain error and differential-phase error
to 0.015% and 0.015°, respectively. They have a 21ns
settling time to 0.1%, 500V/μs slew rates, and output-
current-drive capability of up to 50mA making them ideal
for driving video loads.
Inverting and Noninverting Congurations
Select the gain-setting feedback (RF) and input (RG)
resistor values to fit your application. Large resistor val-
ues increase voltage noise and interact with the ampli-
fier’s input and PCB capacitance. This can generate
undesirable poles and zeros and decrease bandwidth or
cause oscillations. For example, a noninverting gain-of-
two configuration (RF = R
G) using 2kΩ resistors, com-
bined with 1pF of amplifier input capacitance and 1pF of
PCB capacitance, causes a pole at 79.6MHz. Since this
pole is within the amplifier bandwidth, it jeopardizes stabil-
ity. Reducing the 2kΩ resistors to 100Ω extends the pole
frequency to 1.59GHz, but could limit output swing by
adding 200Ω in parallel with the amplifier’s load resistor
(Figures 1a and 1b).
Layout and Power-Supply Bypassing
The MAX4389/MAX4390/MAX4392–MAX4396 operate
from single 4.5V to 11V or from dual ±2.25V to ±5.5V sup-
plies. Bypass each supply with a 0.1μF capacitor as close
to the pin as possible.
Maxim recommends using microstrip and stripline tech-
niques to obtain full bandwidth. To ensure that the PCB
does not degrade the amplifier’s performance, design it
for a frequency greater than 1GHz. Pay careful attention
to inputs and outputs to avoid large parasitic capacitance.
Whether or not you use a constant-impedance board,
observe the following design guidelines:
● Do not use wire-wrap boards; they are too inductive.
● Do not use IC sockets; they increase parasitic capaci-
tance and inductance.
● Use surface-mount instead of through-hole compo-
nents for better, high-frequency performance.
● Use a PCB with at least two layers; it should be as free
from voids as possible.
● Keep signal lines as short and as straight as possible.
Do not make 90° turns; round all corners.
Low-Power Disable Mode
The MAX4389/MAX4393/MAX4394/MAX4396 feature a
disable function that allows the amplifiers to be placed
in a low-power, high-output impedance state. When the
disable pin (DISABLE) is active, the amplifier’s output
impedance is 95kΩ. This high resistance and the low
2pF output capacitance make the MAX4389/MAX4390/
MAX4392–MAX4396 in RF/video multiplexer or switch
applications. For larger arrays, pay careful attention to
capacitive loading (see the Output Capacitive Loading
and Stability section).
Output Capacitive Loading and Stability
The MAX4389/MAX4390/MAX4392–MAX4396 are opti-
mized for AC performance. They are not designed to drive
highly reactive loads, which decrease phase margin and
may produce excessive ringing and oscillation. Figure
2 shows a circuit that eliminates this problem. Figure
3 is a graph of the Optimal Isolation Resistor (RS) vs.
Capacitive Load. Figure 4 shows how a capacitive load
causes excessive peaking of the amplifier’s frequency
response if the capacitor is not isolated from the ampli-
fier by a resistor. A small isolation resistor (usually 10Ω to
15Ω) placed before the reactive load prevents ringing and
oscillation. At higher capacitive loads, AC performance is
controlled by the interaction of the load capacitance and
the isolation resistor. Figure 5 shows the effect of a 15Ω
isolation resistor on closed-loop response.
Figure 1a. Noninverting Gain Configuration
Figure 1b. Inverting Gain Configuration
VIN
RG
VOUT = [1 + (RF / RG)] VIN
RF
VOUT
MAX43_ _
VIN
RG
VOUT = -(RF / RG) VIN
RF
VOUT
MAX43_ _
MAX4389/MAX4390/
MAX4392–MAX4396
Ultra-Small, Low-Cost, 85MHz Op Amps with
Rail-to-Rail Outputs and Disable
www.maximintegrated.com Maxim Integrated
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