ISL59482 Intersil Corporation, ISL59482 Datasheet - Page 11

• Manufacturer Part Number: ISL59482
• Description: Multiplexing Amplifiers
• Manufacturer: Intersil Corporation

V+ SUPPLY
V- SUPPLY
Application Information
General
The ISL59482 is ideal as the matrix element of high
performance switchers and routers. Key features include
internal fixed gain of 2, high impedance buffered analog
inputs and excellent AC performance at output loads down
to 150Ω for video cable-driving. The current feedback output
amplifiers are stable operating into capacitive loads.
Ground Connections
For the best isolation and crosstalk rejection, all GND pins
must connect to the GND plane.
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 28) 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. One
Schottky can be used to protect both V+ power supply pins,
and a second for the protection of both V- pins.
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.
POWER
SIGNAL
LOGIC
DE-COUPLING
GND
CAPS
11
PROTECTION
SCHOTTKY
FIGURE 28. SCHOTTKY PROTECTION CIRCUIT
GND
S0
IN0
IN1
V+
V-
ISL59482
V+
V-
V+
V-
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
Each internal 4:1 triple MUX-amp has a three-state output
control pin (HIZ1 and HIZ2). Each has a an internal pull-
down resistor to set the output to the enabled state with no
connection to the HIZ pin. The HIZ state is established within
approximately 20ns 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. When more than one
MUX shares a common output, the high impedance state
loading effect is minimized over the maximum output voltage
swing and maintains its high Z even in the presence of high
slew rates. The supply current during this state is the same
as the active state.
EN and Power-down States
The EN pin is active low. An internal pull-down resistor
ensures the device will be active with no connection to the
EN pin. The Power-down state is established within
approximately 80ns, if a logic high (>2V) is placed on the EN
pin. In the Power-down state, supply current is reduced
significantly by shutting the three amplifiers off. The output
presents a high impedance to the output pin, however, there
is a risk that the disabled amplifier output can be back-driven
at signal voltage levels exceeding 2V
condition, large incoming slew rates can cause fault currents
of tens of mA. Therefore, the parallel connection of multiple
outputs is not recommended unless the application can
tolerate the limited power-down output impedance.
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.
V+
V-
CONTROL
LOGIC
V+
V-
OUT
P-P
. Under this
December 22, 2006
EXTERNAL
CIRCUITS
FN6209.2