MAX4385E/MAX4386E
Low-Cost, 230MHz, Single/Quad Op Amps with
Rail-to-Rail Outputs and ±15kV ESD Protection
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Detailed Description
The MAX4385E/MAX4386E are single/quad, 5V, rail-to-
rail, voltage-feedback amplifiers that employ current-
feedback techniques to achieve 450V/µs slew rates
and 230MHz bandwidths. High ±15kV ESD protection
guards against unexpected discharge. Excellent har-
monic distortion and differential gain/phase perfor-
mance make these amplifiers an ideal choice for a wide
variety of video and RF signal-processing applications.
Applications Information
The output voltage swings to within 50mV of each sup-
ply rail. Local feedback around the output stage
ensures low open-loop output impedance to reduce
gain sensitivity to load variations. The input stage per-
mits common-mode voltages beyond VEE and to within
2.25V of the positive supply rail.
Choosing Resistor Values
Unity-Gain Configuration
The MAX4385E/MAX4386E are internally compensated
for unity gain. When configured for unity gain, a 24Ω
resistor (RF) in series with the feedback path optimizes
AC performance. This resistor improves AC response
by reducing the Q of the parallel LC circuit formed by
the parasitic feedback capacitance and inductance.
Video Line Driver
The MAX4385E/MAX4386E are low-power, voltage-
feedback amplifiers featuring bandwidths up to
230MHz, 0.1dB gain flatness to 30MHz. They are
designed to minimize differential-gain error and differ-
ential-phase error to 0.02% and 0.01°, respectively.
They have a 14ns settling time to 0.1%, 450V/µs slew
rates, and output-current-drive capability of up to
50mA, making them ideal for driving video loads.
Inverting and Noninverting Configurations
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 amplifi-
er’s input and PC board capacitance. This can
generate undesirable poles and zeros and decrease
bandwidth or cause oscillations. For example, a nonin-
verting gain-of-two configuration (RF= RG) using 1kΩ
resistors, combined with 8pF of amplifier input capaci-
tance and 1pF of PC board capacitance, causes a pole
at 35.4MHz. Since this pole is within the amplifier band-
width, it jeopardizes stability. Reducing the 1kΩresis-
tors to 100Ωextends the pole frequency to 353.8MHz,
but could limit output swing by adding 200Ωin parallel
with the amplifier’s load resistor (Figures 1a
and 1b).
Layout and Power-Supply Bypassing
These amplifiers operate from a single 5V power supply.
Bypass VCC to ground with 0.1µF and 2.2µF capacitors as
close to the pin as possible.
Maxim recommends using microstrip and stripline tech-
niques to obtain full bandwidth. To ensure that the PC
board does not degrade the amplifier’s performance,
design it for a frequency greater than 1GHz. Pay care-
ful attention to inputs and outputs to avoid large para-
sitic capacitance. Regardless of whether 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
capacitance and inductance.
•Use surface mount instead of through-hole compo-
nents for better high-frequency performance.
•Use a PC board with at least two layers; it should be
as free from voids as possible.
•Keep signal lines as short and as straight as possi-
ble. Do not make 90° turns; round all corners.