EL2386 查看數據表（PDF） - Intersil
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EL2386 Datasheet PDF : 13 Pages
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EL2386
loop gains. This feature actually allows the EL2386 to
maintain about the same -3dB bandwidth, regardless of
closed-loop gain. However, as closed-loop gain is increased,
bandwidth decreases slightly while stability increases. Since
the loop stability is improving with higher closed-loop gains,
it becomes possible to reduce the value of RF below the
specified 750Ω and still retain stability, resulting in only a
slight loss of bandwidth with increased closed-loop gain.
Supply Voltage Range and Single-Supply
Operation
The EL2386 has been designed to operate with supply
voltages having a span of greater than 3V, and less than
12V. In practical terms, this means that the EL2386 will
operate on dual supplies ranging from ±1.5V to ±6V. With a
single-supply, the EL2386 will operate from +3V to +12V.
As supply voltages continue to decrease, it becomes
necessary to provide input and output voltage ranges that
can get as close as possible to the supply voltages. The
EL2386 has an input voltage range that extends to within 1V
of either supply. So, for example, on a single +5V supply, the
EL2386 has an input range which spans from 1V to 4V. The
output range of the EL2386 is also quite large, extending to
within 1V of the supply rail. On a ±5V supply, the output is
therefore capable of swinging from -4V to +4V. Single-supply
output range is even larger because of the increased
negative swing due to the external pull-down resistor to
ground. On a single +5V supply, output voltage range is
about 0.3V to 4V.
Video Performance
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency response as DC levels are changed at the output.
This is especially difficult when driving a standard video load
of 150Ω, because of the change in output current with DC
level. Until the EL2386, good Differential Gain could only be
achieved by running high idle currents through the output
transistors (to reduce variations in output impedance).
These currents were typically comparable to the entire 3mA
supply current of each EL2386 amplifier! Special circuitry
has been incorporated in the EL2386 to reduce the variation
of output impedance with current output. This results in dG
and dP specifications of 0.05% and 0.05° while driving 150Ω
at a gain of +2.
Video Performance has also been measured with a 500Ω
load at a gain of +1. Under these conditions, the EL2386 has
dG and dP specifications of 0.01% and 0.01° respectively
while driving 500Ω at AV = +1.
For complete curves, see the Differential Gain and
Differential Phase vs Input Voltage curves.
Output Drive Capability
In spite of its low 3mA of supply current per amplifier, the
EL2386 is capable of providing a minimum of ±50mA of
output current. This output drive level is unprecedented in
amplifiers running at these supply currents. With a minimum
±50mA of output drive, the EL2386 is capable of driving 50Ω
loads to ±2.5V, making it an excellent choice for driving
multiple video loads in RGB applications.
Driving Cables and Capacitive Loads
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, the back-termination series resistor will
decouple the EL2386 from the cable and allow extensive
capacitive drive. However, other applications may have high
capacitive loads without a back-termination resistor. In these
applications, a small series resistor (usually between 5Ω and
50Ω) can be placed in series with the output to eliminate
most peaking. The gain resistor (RG) can then be chosen to
make up for any gain loss which may be created by this
additional resistor at the output. In many cases it is also
possible to simply increase the value of the feedback
resistor (RF) to reduce the peaking.
Current Limiting
The EL2386 has no internal current-limiting circuitry. If an
output is shorted indefinitely, the power dissipation could
easily increase such that the part will be destroyed.
Maximum reliability is maintained if the output current never
exceeds ±60mA. A heat sink may be required to keep the
junction temperature below absolute maximum when an
output is shorted indefinitely.
Multiplexing with the EL2386
The ENABLE pins on the EL2386 allow for multiplexing
applications. Figure 1 shows an EL2386 with all 3 outputs
tied together, driving a back terminated 75Ω video load.
Three sine waves of varying amplitudes and frequencies are
applied to the three inputs, while a 1 of 3 decoder selects
one amplifier to be on at any given time. Figure 2 shows the
resulting output wave form at VOUT. Switching is complete in
about 100ns. Notice the outputs are tied directly together.
De-coupling resistors at each output are not required or
advised when multiplexing.
FIGURE 1.
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