EL2386 データシートの表示（PDF） - Renesas Electronics
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EL2386 Datasheet PDF : 13 Pages
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EL2386
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 750
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 150,
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 150 at a gain of +2.
Video Performance has also been measured with a 500 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 500 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 50 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 5 and 50) 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 75 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.
FN7155 Rev 1.00
June 24, 2004
Page 10 of 13
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