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M
Low-Cost, 230MHz, Single/Quad Op Amps with
Rail-to-Rail Outputs and ±15kV ESD Protection
8
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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 V
EE
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 24
resistor (R
F
) 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 (R
F
) and input (R
G
)
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 (R
F
= R
G
) using 1k
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 1k
resis-
tors to 100
extends the pole frequency to 353.8MHz,
but could limit output swing by adding 200
in 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 V
CC
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.
IN
R
G
V
OUT
= -(R
F
/ R
G
) V
IN
R
F
V
OUT
MAX438_E
Figure 1b. Inverting Gain Configuration
IN
R
G
V
OUT
= [1+ (R
F
/ R
G
)] V
IN
R
F
V
OUT
MAX438_E
Figure 1a. Noninverting Gain Configuration