4

FN3990.8

December 22, 2005

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

table), so give careful consideration to component

placement to minimize trace length. As an example, -3dB

frequency response is obtained by cascading two levels of

crosspoints in the case of multiplexed outputs (see Figure

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