EL2270CS(2004) 데이터 시트보기 (PDF) - Intersil
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EL2270CS Datasheet PDF : 12 Pages
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EL2270
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 EL2270, 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 more than the entire 1mA supply
current of each EL2270 amplifier! Special circuitry has been
incorporated in the EL2270 to reduce the variation of output
impedance with current output. This results in dG and dP
specifications of 0.15% and 0.15° 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 EL2270 has
dG and dP specifications of 0.01% and 0.02° respectively
while driving 500Ω at AV = +1.
Output Drive Capability
In spite of its low 1mA of supply current, each amplifier of the
EL2270 is capable of providing a minimum of ±50mA. These
output drive levels are unprecedented in amplifiers running
at these supply currents. With a minimum ±80mA of output
drive, the ±50mA minimum output drive of each EL2270
amplifier allows swings of ±2.5V into 50Ω loads.
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 EL2270 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 EL2270 has no internal current-limiting circuitry. If any
output is shorted, it is possible to exceed the Absolute
Maximum Ratings for output current or power dissipation,
potentially resulting in the destruction of the device.
Power Dissipation
With the high output drive capability of the EL2270, it is
possible to exceed the 150°C Absolute Maximum junction
temperature under certain very high load current conditions.
Generally speaking, when RL falls below about 25Ω, it is
important to calculate the maximum junction temperature
(TJMAX) for the application to determine if power-supply
voltages, load conditions, or package type need to be
modified for the EL2270 to remain in the safe operating area.
These parameters are calculated as follows [1]:
TJMAX = TMAX + (ΘJA × n × PDMAX)
where:
TMAX = Maximum ambient temperature
θJA = Thermal resistance of the package
n = Number of amplifiers in the package
PDMAX = Maximum power dissipation of each amplifier in
the package
PDMAX for each amplifier can be calculated as follows [2]:
PDMAX
=
(2 × VS × ISMAX) + (VS
-
VOUTM
A
X
)
×
-V----O----U----T----M-----A----X--
RL
where:
VS = Supply voltage
ISMAX = Maximum supply current of 1 amplifier
VOUTMAX = Maximum output voltage of the application
RL = Load resistance
9
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