5
FN3679.12
September 11, 2007
Application Information
General
The HA4314B is a 4x1 crosspoint switch that is ideal for the
matrix element of high performance switchers and routers.
This crosspoint’s low input capacitance and high input
resistance provide excellent video terminations when used
with an external 75Ω resistor. Nevertheless, if several
HA4314B inputs are connected together, the use of an input
buffer should be considered (see Figure 1). This crosspoint
contains no feedback or gain setting resistors, so the output
is a true high impedance load when the IC is disabled
(CS
=1).
Ground Connections
All GND pins are connected to a common point on the die,
so any one of them will suffice as the functional GND
connection. For the best isolation and crosstalk rejection,
however, all GND pins must connect to the GND plane.
Frequency Response
Most applications utilizing the HA4314B require a series
output resistor, R
S
, to tune the response for the specific load
capacitance, C
L
, driven. Bandwidth and slew rate degrade
as C
L
increases (as shown in the “Electrical Specifications”
on page 4), so give careful consideration to component
placement to minimize trace length. In big matrix
configurations where C
L
is large, better frequency response
is obtained by cascading two levels of crosspoints in the
case of multiplexed outputs (see Figure 2), or distributing the
load between two drivers if C
L
is due to bussing and
subsequent stage input capacitance.
Control Signals
CS - This is a TTL/CMOS compatible, active low Chip Select
input. When driven high, CS
forces the output to a true high
impedance state and reduces the power dissipation by a
factor of 25. The CS
input has no on-chip pull-down resistor,
so it must be connected to a logic low (recommend GND) if
the enable function isn’t utilized.
A0, A1 - These are binary coded, TTL/CMOS compatible
address inputs that select which one of the four inputs
connect to the crosspoint output.
Switcher/Router Applications
Figure 1 illustrates one possible implementation of a
wideband, low power, 4x4 switcher/router utilizing the
HA4314B for the switch matrix. A 4x4 switcher/router allows
any of the four outputs to be driven by any one of the four
inputs (e.g., each of the four inputs may connect to a
different output, or an input may connect to multiple outputs).
This application utilizes the HA4600 (video buffer with output
disable) for the input buffer, the HA4314B as the switch
matrix, and the HFA1112 (programmable gain buffer) as the
gain of two output driver. Figure 2 details a 16x1 switcher
(basically a 16:1 mux) which uses the HA4201 (1x1
crosspoint) and the HA4314B in a cascaded stage
configuration to minimize capacitive loading at each output
node, thus increasing system bandwidth.
Power-Up Considerations
No signals should be applied to the analog or digital inputs
before the power supplies are activated. Latch-up may occur
if the inputs are driven at the time of power-up. To prevent
latch-up, the input currents during power-up must not
exceed the values listed in the “Absolute Maximum Ratings”
on page 3.
Intersil’s Crosspoint Family
Intersil offers a variety of 4x1 and 1x1 crosspoint switches. In
addition to the HA4314B, the 4x1 family includes the
HA4404 and HA4344. The HA4404 is a 16 Ld device with
Tally outputs to indicate the selected channel. The HA4344
is a 16 Ld crosspoint with synchronized control lines (A0, A1,
CS
). With synchronization, the control information for the
next channel switch can be loaded into the crosspoint
without affecting the current state. On a subsequent clock
edge the stored control state effects the desired channel
switch.
The 1x1 family is comprised of the HA4201 and HA4600.
They are essentially similar devices, but the HA4201
includes a Tally output (enable indicator). The 1x1s are
useful as high performance video input buffers, or in a switch
matrix requiring very high off isolation.
HA4314B
