ISL59420 Datasheet, PDF (10/12 Pages) Intersil Corporation – 400MHz Multiplexing Amplifier

ISL59420
Ground Connections
For the best isolation and crosstalk rejection, the GND pin
and NIC pins must connect to the GND plane.
Control Signals
S0, ENABLE, HIZ - These pins are TTL/CMOS compatible
control inputs. The S0 pin selects which one of the inputs
connect to the output. The ENABLE, HIZ pins are used to
disable the part to save power and three-state the output
amplifiers, respectively. For control signal rise and fall times
less than 10ns the use of termination resistors close to the
part will minimize transients coupled to the output.
Power-Up Considerations
The ESD protection circuits use internal diodes from all pins
the V+ and V- supplies. In addition, a dV/dT- triggered clamp
is connected between the V+ and V- pins, as shown in the
Equivalent Circuits 1 through 4 section of the Pin Description
table. The dV/dT triggered clamp imposes a maximum
supply turn-on slew rate of 1V/µs. Damaging currents can
flow for power supply rates-of-rise in excess of 1V/µs, such
as during hot plugging. Under these conditions, additional
methods should be employed to ensure the rate of rise is not
exceeded.
Consideration must be given to the order in which power is
applied to the V+ and V- pins, as well as analog and logic
input pins. Schottky diodes (Motorola MBR0550T or
equivalent) connected from V+ to ground and V- to ground
(Figure 23) will shunt damaging currents away from the
internal V+ and V- ESD diodes in the event that the V+
supply is applied to the device before the V- supply.
If positive voltages are applied to the logic or analog video
input pins before V+ is applied, current will flow through the
internal ESD diodes to the V+ pin. The presence of large
decoupling capacitors and the loading effect of other circuits
connected to V+, can result in damaging currents through
the ESD diodes and other active circuits within the device.
Therefore, adequate current limiting on the digital and
analog inputs is needed to prevent damage during the time
the voltages on these inputs are more positive than V+.
HIZ State
An internal pull-down resistor connected to the HIZ pin
ensures the device will be active with no connection to the
HIZ pin. The HIZ state is established within approximately
25ns (Figure 18) by placing a logic high (>2V) on the HIZ
pin. If the HIZ state is selected, the output is a high
impedance 1.4MΩ. Use this state to control the logic 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 basically the same as the active
state.
ENABLE & 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 when a
logic high (>2V) is placed on the ENABLE pin. In the Power
Down state, the output has no leakage but has a large
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 Z state for applications driving more than
one mux on a common output.
Limiting the Output Current
No output short circuit current limit exists on this part. All
applications need to limit the output current to less than
50mA. Adequate thermal heat sinking of the parts is also
required.
V+ SUPPLY
LOGIC
POWER
GND
SIGNAL
DE-COUPLING
CAPS
V- SUPPLY
SCHOTTKY
PROTECTION
V+
S0
GND V- V+
IN0
V+
V-
IN1
V-
V+
LOGIC
CONTROL
V-
V+
OUT
V-
FIGURE 26. SCHOTTKY PROTECTION CIRCUIT
EXTERNAL
CIRCUITS
10
FN7459.1
September 22, 2005