EL2003 INTERSIL [Intersil Corporation], EL2003 Datasheet - Page 5

• Manufacturer Part Number: EL2003
• Description: 100MHz Video Line Driver
• Manufacturer: INTERSIL [Intersil Corporation]

Applications Information
The EL2003 and EL2033 are monolithic buffer amplifiers
built with Elantec's proprietary dielectric isolation process
that produces NPN and PNP complimentary transistors. The
circuits are connection of symmetrical common collector
transistors that provide both sink and source current
capability independent of output voltage while maintaining
constant output and input impedances. The high slew rate
and wide bandwidth of the EL2003 and EL2033 make them
useful beyond video frequencies.
Power Supplies
The EL2003 and EL2033 may be operated with single or
split supplies as low as ±2.5V (5V total) to as high as ±18V
(36V total). However, the bandwidth, slew rate, and output
impedance degrade significantly for supply voltages less
than ±5V (10V total) as shown in the characteristic curves. It
is not necessary to use equal value split supplies, for
example -5V and +12V would be excellent for 0V to 1V video
signals.
Bypass capacitors from each supply pin to a ground plane
are recommended. The EL2003 and EL2033 will not
oscillate even with minimal bypassing, however, the supply
will ring excessively with inadequate capacitance. To
eliminate a supply ringing and the interference it can cause,
a 10µF tantalum capacitor with short pins is recommended
for both supplies. Inadequate supply bypassing can also
result in lower slew rates and longer settling times.
Input Range
The input to the EL2003 and EL2033 looks like a high
resistance in parallel with a few picofarads in addition to a
DC bias current. The input characteristics change very little
with output loading, even when the amplifier is in current
limit. However, there are clamp diodes from the input to the
output that protect the transistor base emitter junctions.
These diodes start to conduct at about ±9.5V input to output
differential voltage. Of course the input resistance drops
dramatically when the diodes start conducting; the diodes
are rated at ±50mA.
The input characteristics also change when the input voltage
exceeds either supply by 0.5V. This happens because the
input transistor's base-collector junctions forward bias. If the
input exceeds the supply by LESS than 0.5V and then
returns to the normal input range, the output will recover in
less than 10ns. However, if the input exceeds the supply by
MORE than 0.5V, the recovery time can be hundreds of
nanoseconds. For this reason it is recommended that
schottky diode clamps from input to supply be used if a fast
recovery from large input overloads is required.
5
EL2003, EL2033
Source Impedance
The EL2003 and EL2033 have excellent input-output
isolation and are very tolerant of variations in source
impedances. Capacitive sources cause no problems at all,
resistive sources up to 100kΩ present no problems as long
as care is used in board layout to minimize output to input
coupling. Inductive sources can cause oscillations; a 1kΩ
resistor in series with the buffer input pin will usually
eliminate problems without sacrificing too much speed. An
unterminated cable or other resonant source can also cause
oscillations. Again, an isolating resistor will eliminate the
problem.
Current Limit
The EL2003 and EL2033 have internal current limits that
protect the output transistors. The current limit goes down
with junction temperature rise as shown in the characteristic
curves. At a junction temperature of +175°C the current
limits are at about 100mA. If the EL2003 or EL2033 output is
shorted to ground when operating on ±15V supplies, the
power dissipation will be greater than 1.5W. A heat sink is
required in order for the EL2003 or EL2033 to survive an
indefinite short. Recovery time to come out of current limit is
about 250ns.
Heat Sinking
When operating the EL2003 and EL2033 in elevated
ambient temperatures and/or high supply voltages and low
impedance loads, the internal power dissipation can force
the junction temperature above the maximum rating (150°C
for the plastic DIP). Also, an indefinite short of the output to
ground will cause excessive power dissipation.
The thermal resistance junction to case is 50°C/W for the
plastic DIP. A suitable heat sink will increase the power
dissipation capability significantly beyond that of the package
alone. Several companies make standard heat sinks for both
packages. Aavid and Thermalloy heat sinks have been used
successfully.
Parallel Operation
If more than 100mA output is required or if heat
management is a problem, several EL2003 or EL2033s may
be paralleled together. The result is as though each device
was driving only part of the load. For example, if two units
are paralleled then a 50Ω load looks like 100Ω to each
EL2003. Parallel operation results in lower input and output
impedances, increased bias current but no increase in offset
voltage. An example showing three EL2003s in parallel and
also the addition of a FET input buffer stage is shown below.
By using a dual FET the circuit complexity is minimal and the
performance is excellent. Take care to minimize the stray
capacitance at the input of the EL2003s for maximum slew
rate and bandwidth.