M
High-S peed, Low-Power, S ingle-S upply,
Multic hannel, Video Multiplexer-Amplifiers
______________________________________________________________________________________
13
Low-Power S hutdown Mode
All parts feature a low-power shutdown mode that is
activated by driving the
SHDN
input low. Placing the
amplifier in shutdown mode reduces the quiescent sup-
ply current to 560μA and places the output into a high-
impedance state, typically 35k
. By tying the outputs
of several devices together and disabling all but one of
the paralleled amplifiers’ outputs, multiple devices may
be paralleled to construct larger switch matrices.
For MAX4310/MAX4311/MAX4312 application circuits
operating with a closed-loop gain of +2V/V or greater,
consider the external-feedback network impedance of
all
devices used in the mux application when calculat-
ing the total load on the output amplifier of the active
device. The MAX4313/MAX4314/MAX4315 have a fixed
gain of +2V/V that is internally set with two 500
thin-
film resistors. The impedance of the internal feedback
resistors must be taken into account when operating
multiple MAX4313/MAX4314/MAX4315s in large multi-
plexer applications.
For normal operation, drive
SHDN
high. If the shutdown
function is not used, connect
SHDN
to V
CC
.
Layout and Power-S upply Bypassing
The MAX4310–MAX4315 have very high bandwidths
and consequently require careful board layout, includ-
ing 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. Therefore, layers that do not incorporate a
signal or power trace should not have a ground plane.
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 (they are too
inductive) or breadboards (they are too capacitive).
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.
OUT
IN-
SHDN, A0, A1, A2
IN+
10k
LOGIC INPUT
MAX431_
Figure 3. Circuit to Reduce Logic-Low Input Current
0
-10
0
50 100 150
LOGIC-LOW THRESHOLD (mV ABOVE V
EE
)
300 350
500
-7
-8
-1
I
μ
A
200 250
400 450
-3
-5
-9
-2
-4
-6
Figure 4. Logic-Low Input Current vs. V
IL
with 10k
Series
Resistor
20
-160
0
50 100 150
LOGIC-LOW THRESHOLD (mV ABOVE V
EE
)
300 350
500
-100
-120
0
I
μ
A
200 250
400 450
-60
-140
-20
-40
-80
Figure 2. Logic-Low Input Current vs. V
IL
(
SHDN
, A0, A1, A2)