el4342 Intersil Corporation, el4342 Datasheet - Page 10

• Manufacturer Part Number: el4342
• Description: 500mhz Triple, Multiplexing Amplifier
• Manufacturer: Intersil Corporation

HIZ State
An internal pull-down resistor ensures the device will be
active with no connection to the HIZ pin. The HIZ state is
established within approximately 15ns (Figure 16) by placing
a logic high (>2V) on the HIZ pin. If the HIZ state is selected,
the output is a high impedance 1.4MΩ with approximately
1.5pF in parallel with a 10µA bias current from the output.
Use this state when more than one mux shares a common
output.
In the HIZ state the output is three-stated, and maintains its
high Z even in the presence of high slew rates. The supply
current during this state is same as the active state.
ENABLE and Power-down States
The enable pin is active low. An internal pull-down resistor
ensures the device will be active with no connection to the
ENABLE pin. The Power-down state is established within
approximately 80ns (Figure 14), if a logic high (>2V) is
placed on the ENABLE pin. In the Power-down state, the
output has no leakage but has a large variable capacitance
(on the order of 15pF), and is capable of being back-driven.
Under this condition, large incoming slew rates can cause
fault currents of tens of mA. Do not use this state as a high
impedance output when several MUX amps share the
same output line.
LE State
The EL4340 is equipped with a Latch Enable pin. A logic
high (>2V) on the LE pin latches the last logic state. This
logic state is preserved when cycling HIZ or ENABLE
functions.
Limiting the Output Current
No output short circuit current limit exists on these parts. All
applications need to limit the output current to less than
50mA. Adequate thermal heat sinking of the parts is also
required.
Application Example
Figure 22 illustrates the use of the EL4342, two ISL84517
SPST switches and one NC7ST00P5X NAND gate to mux 3
different component video signals and one RGB video
signal. The SPDT switches provide the sync signal for the
RGB video and disconnects the sync signal for the
component signal.
PC Board Layout
The AC performance of this circuit depends greatly on the
care taken in designing the PC board. The following are
recommendations to achieve optimum high frequency
performance from your PC board.
• The use of low inductance components such as chip
• Minimize signal trace lengths. Trace inductance and
resistors and chip capacitors is strongly recommended.
capacitance can easily limit circuit performance. Avoid
10
EL4340, EL4342
• Match channel-channel analog I/O trace lengths and
• Maximize use of AC de-coupled PCB layers. All signal I/O
• Use proper value and location of termination resistors.
• When testing use good quality connectors and cables,
• Minimum of 2 power supply de-coupling capacitors are
• The NIC pins are placed on both sides of the input pins.
The QFN Package Requires Additional PCB Layout
Rules for the Thermal Pad
The thermal pad is electrically connected to V- supply
through the high resistance IC substrate. Its primary function
is to provide heat sinking for the IC. However, because of the
connection to the V- supply through the substrate, the
thermal pad must be tied to the V- supply to prevent
unwanted current flow to the thermal pad. Do not tie this pin
to GND as this could result in large back biased currents
flowing between GND and V-. The EL4342 uses the package
with pad dimensions of D2 = 2.48mm and E2 = 3.4mm.
Maximum AC performance is achieved if the thermal pad is
attached to a dedicated de-coupled layer in a multi-layered
PC board. In cases where a dedicated layer is not possible,
AC performance may be reduced at upper frequencies.
The thermal pad requirements are proportional to power
dissipation and ambient temperature. A dedicated layer
eliminates the need for individual thermal pad area. When a
dedicated layer is not possible a 1” x 1” pad area is sufficient
for the EL4342 that is dissipating 0.5W in +50°C ambient.
Pad area requirements should be evaluated on a case by
case basis.
sharp corners, use rounded corners when possible. Vias
in the signal lines add inductance at high frequency and
should be avoided. PCB traces greater than 1" begin to
exhibit transmission line characteristics with signal rise/fall
times of 1ns or less. High frequency performance may be
degraded for traces greater than one inch, unless strip line
are used.
layout symmetry. This will minimize propagation delay
mismatches.
lines should be routed over continuous ground planes (i.e.
no split planes or PCB gaps under these lines). Avoid vias
in the signal I/O lines.
Termination resistors should be as close to the device as
possible.
matching cable types and keeping cable lengths to a
minimum.
recommended (1000pF, 0.01µF) as close to the devices
as possible - Avoid vias between the cap and the device
because vias add unwanted inductance. Larger caps can
be farther away. When vias are required in a layout, they
should be routed as far away from the device as possible.
These pins are not internally connected to the die. It is
recommended these pins be tied to ground to minimize
crosstalk.
February 23, 2006
FN7421.2