EL2270CS Просмотр технического описания (PDF) - Intersil
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EL2270CS Datasheet PDF : 14 Pages
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EL2170, EL2270, EL2470
acceptable with the Metal-Film resistors giving slightly less
peaking and bandwidth because of their additional series
inductance. Use of sockets, particularly for the SO package
should be avoided if possible. Sockets add parasitic
inductance and capacitance which will result in some
additional peaking and overshoot.
Capacitance at the Inverting Input
Any manufacturer's high-speed voltage- or current-feedback
amplifier can be affected by stray capacitance at the
inverting input. For inverting gains this parasitic capacitance
has little effect because the inverting input is a virtual
ground, but for non-inverting gains this capacitance (in
conjunction with the feedback and gain resistors) creates a
pole in the feedback path of the amplifier. This pole, if low
enough in frequency, has the same destabilizing effect as a
zero in the forward open-loop response. The use of large
value feedback and gain resistors further exacerbates the
problem by further lowering the pole frequency.
The experienced user with a large amount of PC board
layout experience may find in rare cases that the EL2170,
EL2270, and EL2470 have less bandwidth than expected.
The reduction of feedback resistor values (or the addition of
a very small amount of external capacitance at the inverting
input, e.g. 0.5pF) will increase bandwidth as desired. Please
see the curves for Frequency Response for Various RF and
RG, and Frequency Response for Various CIN-.
Feedback Resistor Values
The EL2170, EL2270, and EL2470 have been designed and
specified at gains of +1 and +2 with RF = 1kΩ. This value of
feedback resistor gives 70MHz of -3dB bandwidth at AV = +1
with about 1.5dB of peaking, and 60MHz of -3dB bandwidth
at AV = +2 with about 0.5dB of peaking. Since the EL2170,
EL2270, and EL2470 are current-feedback amplifiers, it is
also possible to change the value of RF to get more
bandwidth. As seen in the curve of Frequency Response For
Various RF and RG, bandwidth and peaking can be easily
modified by varying the value of the feedback resistor.
Because the EL2170, EL2270, and EL2470 are current-
feedback amplifiers, their gain-bandwidth product is not a
constant for different closed-loop gains. This feature actually
allows the EL2170, EL2270, and EL2470 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 1kΩ 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 EL2170, EL2270, and EL2470 have 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
EL2170, EL2270, and EL2470 will operate on dual supplies
ranging from ±1.5V to ±6V. With a single-supply, the EL2170,
EL2270, and EL2470 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
EL2170, EL2270, and EL2470 have an input voltage range
that extends to within 1V of either supply. So, for example, on
a single +5V supply, the EL2170, EL2270, and EL2470 have
an input range which spans from 1V to 4V. The output range
of the EL2170, EL2270, and EL2470 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 EL2170, EL2270, and EL2470, 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 EL2170, EL2270,
and EL2470 amplifier! Special circuitry has been
incorporated in the EL2170, EL2270, and EL2470 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 EL2170,
EL2270, and EL2470 have 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, the EL2170 is
capable of providing a minimum of ±80mA of output current.
Similarly, each amplifier of the EL2270 and the EL2470 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
EL2170 is capable of driving 50Ω loads to ±4V, making it an
excellent choice for driving isolation transformers in
telecommunications applications. Similarly, the ±50mA
minimum output drive of each EL2270 and EL2470 amplifier
allows swings of ±2.5V into 50Ω loads.
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