LMH6584 Datasheet, PDF (16/20 Pages) National Semiconductor (TI) – 32x16 400 MHz Analog Crosspoint Switches, Gain of 1, Gain of 2

DAISY CHAIN OPTION IN SERIAL MODE
The LMH6584/LMH6585 support daisy chaining of the serial
data stream between multiple chips. This feature is available
only in the Serial Programming Mode. To use this feature se-
rial data is clocked into the first chip D_IN pin, and the next chip
D_IN pin is connected to the D_OUT pin of the first chip. Both chips
may share a Chip Select signal, or the second chip can be
enabled separately. When the Chip Select pin goes low on
both chips a double length word is clocked into the first chip.
As the first word is clocking into the first chip, the second chip
is receiving the data that was originally in the shift register of
the first chip (invalid data). When a full 96 bits have been
clocked into the first chip the next clock cycle begins moving
the first frame of the new configuration data into the second
chip. With a full 192 clock cycles both chips have valid data
and the Chip Select pin of both chips should be brought high
to prevent the data from overshooting. A configure pulse will
activate the new configuration on both chips simultaneously,
or each chip can be configured separately. The mode, Chip
Select, configure, and clock pins of both chips can be tied
together and driven from the same sources.
Timing Diagram for Daisy Chain Operation
30045012
SPECIAL CONTROL PINS
should be budgeted 30 mW of power. For a typical application
The LMH6584/LMH6585 have two special control pins that
function independent of the serial control bus. One of these
pins is the reset (RST) pin. The RST pin is active high mean-
ing that at a logic 1 level the chip is configured with all outputs
disabled and in a high impedance state. The RST pin pro-
grams all the registers with input address 0 and all the outputs
are turned off. In this configuration the device draws only 40
mA. The reset pin can be used as a shutdown function to re-
duce power consumption. The other special control pin is the
broadcast (BCST) pin. The BCST pin is also active high and
sets all the outputs to the on state connected to input 0. Both
of these pins are level sensitive and require no clock signal.
The two special control pins overwrite the contents of the
configuration register.
with one video load for each output this would be a total power
of 2.5W. With a typical θ_JA of 22°C/W this will result in the
silicon being 55°C over the ambient temperature. A more ag-
gressive application would be two video loads per output
which would result in 3W of power dissipation. This would re-
sult in a 66°C temperature rise. The QFP package thermal
performance can be significantly enhanced with an external
heat sink and by providing for moving air ventilation. Also, be
sure to calculate the increase in ambient temperature from all
devices operating in the system case. Because of the high
power output of this device, thermal management should be
considered very early in the design process. Generous pas-
sive venting and vertical board orientation may avoid the need
for fan cooling provided a large heat sink is used. Also, the
LMH6584/LMH6585 can be operated with a ±3.3V power
THERMAL MANAGEMENT
supply. This will cut power dissipation substantially while only
The LMH6584/LMH6585 are high performance device that
produces a significant amount of heat. With a ±5V supply, the
reducing bandwidth by about 10% (2 V_PP output). The
LMH6584/LMH6585 are fully characterized and factory tested
LMH6584/LMH6585 will dissipate approximately 2W of idling
at the ±3.3V power supply condition for applications where
power with all outputs enabled. Idling power is calculated
reduced power is desired.
based on the typical supply current of 200 mA and a 10V
The recommended heat sink is AAVD/Thermalloy part #
supply voltage. This power dissipation will vary within the
375024B60024G. This heat sink is designed to be used with
range of 1.8W to 2.2W due to process variations. In addition,
solder anchors #125700D00000G. This heat sink is larger
each equivalent video load (150Ω) connected to the outputs
then the LMH6584/LMH6585 package in order to provide
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