4
FN3990.9
April 25, 2013
Application Information
General
The HA4600 is a unity gain buffer that is optimized for high
performance video applications. The output disable function
makes it ideal for the matrix element in small, high input-to-
output isolation switchers and routers. This buffer contains no
feedback or gain setting resistors, so the output is a true high
impedance load when the IC is disabled (EN = 0). The HA4600
also excels as an input buffer for routers with a large number of
outputs (i.e. each input must connect to a large number of
outputs) and delivers performance superior to most video
amplifiers at a fraction of the cost. As an input buffer, the
HA4600’s low input capacitance and high input resistance
provide excellent video terminations when used with an
external 75
Ω resistor.
Frequency Response
Most applications utilizing the HA4600 require a series
output resistor, RS, to tune the response for the specific load
capacitance, CL, driven. Bandwidth and slew rate degrade
as CL increases (as shown in the Electrical Specification
table), so give careful consideration to component
placement to minimize trace length. As an example, -3dB
bandwidth decreases to 160MHz for CL = 100pF, RS =0Ω.
In big matrix configurations where CL 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 CL is due to
bussing and subsequent stage input capacitance.
Control Signals
EN - The ENABLE input is a TTL/CMOS compatible, active
high input. When driven low this input forces the output to a
true high impedance state and reduces the power
dissipation by two orders of magnitude. The EN input has no
on-chip pull-up resistor, so it must be connected to a logic
high (recommend V+) if the enable function isn’t utilized.
Switcher/Router Applications
Figure 1 illustrates one possible implementation of a
wideband, low power, 4 x 4 switcher/router. A 4 x 4
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 for the
input buffer, the HA4404 (4 x 1 crosspoint switch) as the
switch matrix, and the HFA1112 (programmable gain buffer)
as the gain of two output driver. Figure 2 details a 16 x 1
switcher (basically a 16:1 MUX) which uses the HA4600 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.
Intersil’s Crosspoint Family
Intersil offers a variety of 1 x 1 and 4 x 1 crosspoint switches. In
addition to the HA4600, the 1 x 1 family includes the HA4201
which is an essentially similar device that includes a Tally output
(enable indicator). The 4 x 1 family is comprised of the HA4314,
HA4404, and HA4344. The HA4314 is a 14 lead basic 4 x 1
crosspoint. The HA4404 is a 16 lead device with Tally outputs
to indicate the selected channel. The HA4344 is a 16 lead
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.
HA4600