EL2020CN View Datasheet(PDF) - Intersil
Part Name
Description
MFG CO.
EL2020CN Datasheet PDF : 14 Pages
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EL2020
Current Limit
The EL2020 has internal current limits that protect the output
transistors. The current limit goes down with junction
temperature rise. At a junction temperature of +175°C the
current limits are at about 50mA. If the EL2020 output is
shorted to ground when operating on ±15V supplies, the
power dissipation could be as great as 1.1W. A heat sink is
required in order for the EL2020 to survive an indefinite
short. Recovery time to come out of current limit is about
50ns.
Using the EL2020 with Output Buffers
When more output current is required, a wideband buffer
amplifier can be included in the feedback loop of the
EL2020. With the EL2003 the subsystem overshoots about
10% due to the phase lag of the EL2003. With the EL2004 in
the loop, the overshoot is less than 2%. For even more
output current, several buffers can be paralleled.
EL2020 BUFFERED WITH AN EL2004
Capacitive Loads
The EL2020 is like most high speed feedback amplifiers in
that it does not like capacitive loads between 50pF and
1000pF. The output resistance works with the capacitive load
to form a second non-dominate pole in the loop. This results
in excessive peaking and overshoot and can lead to
oscillations. Standard resistive isolation techniques used
with other op amps work well to isolate capacitive loads from
the EL2020.
Offset Adjust
To calculate the amplifier system offset voltage from input to
output we use the equation:
Output Offset Voltage = VOS (RF/RG+1) ± IBIAS (RF)
The EL2020 output offset can be nulled by using a 10kΩ
potentiometer from pins 1 to 5 with the slider tied to pin 7
(+VCC). This adjusts both the offset voltage and the inverting
input bias current. The typical adjustment range is ±80mV at
the output.
Compensation
The EL2020 is internally compensated to work with external
feedback resistors for optimum bandwidth over a wide range
of closed loop gain. The part is designed for a nominal 1kΩ
of feedback resistance, although it is possible to get more
bandwidth by decreasing the feedback resistance.
The EL2020 becomes less stable by adding capacitance in
parallel with the feedback resistor, so feedback capacitance
is not recommended.
The EL2020 is also sensitive to stray capacitance from the
inverting input to ground, so the board should be laid out to
keep the physical size of this node small, with ground plane
kept away from this node.
Active Filters
The EL2020’s low phase lag at high frequencies makes it an
excellent choice for high performance active filters. The filter
response more closely approaches the theoretical response
than with conventional op amps due to the EL2020’s smaller
propagation delay. Because the internal compensation of the
EL2020 depends on resistive feedback, the EL2020 should
be set up as a gain block.
Driving Cables
The EL2020 was designed with driving coaxial cables in
mind. With 30mA of output drive and low output impedance,
driving one to three 75Ω double terminated coax cables with
one EL2020 is practical. Since it is easy to set up a gain of
+2, the double matched method is the best way to drive coax
cables, because the impedance match on both ends of the
cable will suppress reflections. For a discussion on some of
the other ways to drive cables, see the section on driving
cables in the EL2003 data sheet.
Video Performance Characteristics
The EL2020 makes an excellent gain block for video
systems, both RS-170 (NTSC) and faster. It is capable of
driving 3 double terminated 75Ω cables with distortion levels
acceptable to broadcasters. A common video application is
to drive a 75Ω double terminated coax with a gain of 2.
To measure the video performance of the EL2020 in the non-
inverting gain of 2 configuration, 5 identical gain-of-two
circuits were cascaded (with a divide by two 75Ω attenuator
between each stage) to increase the errors.
The results, shown in the photos, indicate the entire system
of 5 gain-of-two stages has a differential gain of 0.5% and a
differential phase of 0.5°. This implies each device has a
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