MAX458-MAX459 MAXIM [Maxim Integrated Products], MAX458-MAX459 Datasheet - Page 13

• Manufacturer Part Number: MAX458-MAX459
• Description: 8x4 Video Crosspoint Switches with Buffers
• Manufacturer: MAXIM [Maxim Integrated Products]

As with all analog circuits, good PC board layout, prop-
er grounding, and careful component selection are cru-
cial for realizing the full AC performance of high-speed
amplifiers such as the MAX458/MAX459. For optimal
performance:
1) Use a large, low-impedance analog ground plane.
2) Minimize trace area at the circuit’s critical high-imped-
3) Connect the coaxial-cable shield to the ground side
4) Bypass all power-supply pins directly to the ground
Figure 10. SPI/QSPI Connection
__________Applications Information
With multilayer boards, the ground plane(s) should
be located on the layer that does not contain signal
traces. Connect all GND pins to the analog ground
plane.
ance nodes to prevent unwanted signal coupling.
Surround analog inputs with an AC ground trace
(bypassed DC power supply, etc.). The analog input
pins of the MAX458/MAX459 have been separated
with AC ground pins (GND, V
parasitic coupling, which can degrade crosstalk.
of the 75Ω terminating resistor at the ground plane
to further reduce crosstalk (Figure 11).
plane with 0.1µF ceramic capacitors placed as
close to the supply pins as possible. For high-cur-
rent loads, you may need 10µF tantalum or alu-
minum-electrolytic capacitors in parallel with the
0.1µF ceramics. Keep capacitor lead lengths as
short as possible to minimize series inductance; sur-
face-mount chip capacitors are ideal.
THE DOUT-MOSO CONNECTION IS NOT REQUIRED FOR
WRITING TO THE MAX458/MAX459, BUT MAY BE USED
FOR DATA-ECHO PURPOSES.
8x4 Video Crosspoint Switches with Buffers
MAX458
MAX459
______________________________________________________________________________________
DOUT
SCLK
DIN
CS
Grounding and Bypassing,
SCK
MOSI
I/O
MOSO
CPOL = 0, CPHA = 0
PC Board Layout
CC
, V
SPI/QSPI
PORT
EE
) to minimize
The MAX458/MAX459 assume a high-impedance state
on power-up if the inputs are not being programmed to
any particular state during that time. They also are in a
high-impedance state when disabled. This feature
makes it possible to create larger arrays than 8x4 with-
out special programming, other than ensuring that your
program doesn’t turn on two paralleled outputs simulta-
neously. Testing has shown no degradation of differen-
tial gain or phase when the outputs are connected in
parallel.
The MAX458/MAX459’s input registers remain active dur-
ing shutdown, which allows the crosspoint to be pro-
grammed while the devices are shut down. As a result, all
outputs may be simultaneously brought to any state,
including disabled. Just program all of the MAX458/
MAX459s into shutdown, and enter the program of your
choice by selecting the desired inputs and outputs. Taking
SHDN low takes the device(s) out of shutdown.
A power-on reset circuit causes the output amplifiers to
power up in the disabled mode, whether or not SHDN
is applied, if
The number of MAX458s that can be paralleled is limit-
ed by capacitive loading on each output, which must
not exceed 100pF. Each input presents approximately
7pF of load, and each output presents approximately
12pF. Therefore, the MAX458/MAX459 will drive a maxi-
mum of 14 inputs, or 7 outputs and 2 inputs, or any
other combination resulting in less than a 100pF load.
Adding isolation resistors enables more MAX458s to be
paralleled (see the Driving Capacitive Loads section).
Figure 11. Low-Crosstalk Layout. Return current from termina-
tion resistor does not flow through the ground plane.
–
U
—
P
—
D
—
A
—
T
—
E
–
and
RETURN
CURRENT
RETURN
CURRENT
Creating Larger Arrays
–
C
—
S
–
are high.
IN_
IN_
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