MAX4023–MAX4026
Triple and Quad, 2:1 Video Multiplexer-
Amplifiers with Fixed and Settable Gain
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Detailed Description
The MAX4024/MAX4026 combine three and four 2:1
multiplexers, respectively, with a fixed gain of 2 amplifi-
er. The MAX4023/MAX4025 combine three and four 2:1
multiplexers, respectively, with an adjustable gain out-
put amplifier optimized for a closed-loop gain of +1 or
greater. These devices operate from a single-supply
voltage of +4.5V to +11V or from dual supplies of
±2.25V to ±5.5V. The outputs may be placed in a high-
impedance state and the supply current minimized by
forcing the EN pin low. The input multiplexers feature
short 25ns channel-switching times and small 10mV
P-P
switching transients. These devices feature voltage-
feedback output amplifiers that achieve up to 363V/µs
slew rates and up to 220MHz -3dB bandwidths. They
also feature excellent differential gain/phase perfor-
mance.
The MAX4023–MAX4026 feature an A/B pin, which is
an input pin for selecting either channel A or B. Drive
A/B high to select channel A or drive A/B low to select
channel B. Channel A is automatically selected if A/B is
left unconnected.
Applications Information
Feedback and Gain Resistor Selection
(MAX4023/MAX4025)
Select the MAX4023/MAX4025 gain-setting feedback
R
F
and R
G
resistors to fit your application. Large resis-
tor values increase voltage noise and interact with the
amplifier’s input and PC board capacitance. This can
generate undesirable poles and zeros, and can
decrease bandwidth or cause oscillations.
Stray capacitance at the FB pin produces peaking in
the frequency-response curve. Keep the capacitance
at FB as low as possible by using surface-mount resis-
tors and by avoiding the use of a ground plane beneath
or beside these resistors and the FB pin. Some capaci-
tance is unavoidable. If necessary, its effects can be
neutralized by adjusting R
F
. Use 1% resistors to main-
tain gain accuracy.
Low-Power Shutdown Mode
All parts feature a low-power shutdown mode that is
activated by driving the EN input low. Placing the
amplifier in shutdown mode reduces the quiescent sup-
ply current to below 4mA and places the output into a
high-impedance state, typically 75kΩ (MAX4023/
MAX4025). Multiple devices may be paralleled to con-
struct larger switch matrices by connecting the outputs
of several devices together and disabling all but one of
the paralleled amplifiers’ outputs.
For MAX4023/MAX4025 application circuits operating
with a closed-loop gain of +1 or greater, consider the
external-feedback network impedance of all devices
used in the mux application when calculating the total
load on the output amplifier of the active device. The
MAX4024/MAX4026 have a fixed gain of +2 that is
internally set with two 500Ω thin-film resistors. The
impedance of the internal feedback resistors must be
taken into account when operating multiple MAX4024/
MAX4026s in large multiplexer applications.
For normal operation, drive EN high. Note that the
MAX4023–MAX4026 have internal pullup circuitry on
EN, so if left unconnected, it is automatically pulled up
to V
CC
.
Layout and Power-Supply Bypassing
The MAX4023–MAX4026 have high bandwidths and
consequently require careful board layout, including
the possible use of constant-impedance microstrip or
stripline techniques.
To realize the full AC performance of these high-speed
amplifiers, pay careful attention to power-supply
bypassing and board layout. The PC board should
have at least two layers: a signal and power layer on
one side, and a large, low-impedance ground plane on
the other side. The ground plane should be as free of
voids as possible, with one exception: The feedback
(FB) should have as low a capacitance to ground as
possible. Whether or not a constant-impedance board
is used, it is best to observe the following guidelines
when designing the board:
1) Do not use wire-wrapped boards or breadboards.
2) Do not use IC sockets; they increase parasitic
capacitance and inductance.
3) Keep signal lines as short and straight as possible.
Do not make 90° turns; round all corners.
4) Observe high-frequency bypassing techniques to
maintain the amplifier’s accuracy and stability.
5) Use surface-mount components. They generally
have shorter bodies and lower parasitic reactance,
yielding better high-frequency performance than
through-hole components.
The bypass capacitors should include a 0.1µF ceramic
surface-mount capacitor between each supply pin and
the ground plane, located as close to the package as
possible. Optionally, place a 10µF tantalum capacitor
at the power-supply’s point of entry to the PC board to
ensure the integrity of incoming supplies. The power-
supply traces should lead directly from the tantalum
capacitor to the V
CC
and V
EE
pins. To minimize para-
