MAX498 Datasheet, PDF (13/16 Pages) Maxim Integrated Products – Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers

Quad/Triple, SPDT, RGB Switches
with 250MHz Video Buffer Amplifiers
Another option for output disable is to connect LE to V+,
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MAX498/MAX499s, and
devices but the one in
use
use
(Figure 8b).
When the outputs are disabled, off-isolation from the
analog inputs to the amplifier outputs is typically 81dB
at 10MHz.
Grounding and Layout
The MAX498/MAX499 bandwidths are in the RF fre-
quency range. Depending on the size of the PC board
used and the frequency of operation, it may be neces-
sary to use Micro-strip or Stripline techniques.
To realize the full AC performance of these high-speed
buffers, pay careful attention to power-supply bypassing
and board layout. The PC board should have at least two
layers (wire-wrap boards are too inductive, and bread
boards are too capacitive), with one side a signal layer
and the other a large, low-impedance ground plane. With
multilayer boards, locate the ground plane on the layer
that is not dedicated to a specific signal trace. The ground
plane should be as free from voids as possible. Connect
all ground pins to the ground plane.
Connect both positive power-supply pins together and
bypass with a 0.10µF ceramic capacitor at each power-
supply pin, as close to the device as possible. Repeat
for the negative power-supply pins. The capacitor lead
lengths should be as short as possible to minimize lead
inductance; surface-mount chip capacitors are ideal. A
large-value (10µF or greater) tantalum or electrolytic
bypass capacitor on each supply may be required for
high-current loads. The location of this capacitor is not
critical.
The MAX498/MAX499’s analog input pins are isolated
with ground pins to minimize parasitic coupling, which can
degrade crosstalk and/or amplifier stability. Keep signal
paths as short as possible to minimize inductance. Ensure
that all input channel traces are the same length, to main-
tain the phase relationship between the four channels. To
further reduce crosstalk, connect the coaxial-cable shield
to the ground side of the 75Ω terminating resistor at the
ground plane, and terminate all unused inputs to ground
and outputs with a 100Ω or 150Ω resistor to ground.
Table 1a. Amplifier and Channel
Selection with LE = V+
CS EN A0
FUNCTION
0
0
0
Enables amplifier outputs. Selects
channel A.
0
0
1
Enables amplifier outputs. Selects
channel B.
0
1
X Disables amplifiers. Outputs high-Z.
1
X
X Latches A0, EN. Outputs unchanged.
Table 1b. Amplifier and Channel
Selection with LE = GND
CE EN A0
FUNCTION
0
0
0
Enables amplifier outputs. Selects
channel A.
Enables amplifier outputs. Latches A0
1
0
X
tsotaoteutaptuCt—AS–’sorlaBs,t
according
edge.
to
A0’s
X
1
X
Disables amplifiers. Outputs high-Z.
A0 latch = channel A.
0
0
1
Enables amplifier outputs. Selects
channel B.
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