EL2270CS(2004) 데이터 시트보기 (PDF) - Intersil
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EL2270CS Datasheet PDF : 12 Pages
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EL2270
Applications Information
Product Description
The EL2270 is a current-feedback operational amplifier that
offers a wide -3dB bandwidth of 70MHz and a low supply
current of 1mA per amplifier. This product also features high
output current drive. The EL2270 can output 55mA per
amplifier and works with supply voltages ranging from a
single 3V to ±6V, and is also capable of swinging to within 1V
of either supply on the input and the output. Because of its
current-feedback topology, the EL2270 does not have the
normal gain-bandwidth product associated with voltage-
feedback operational amplifiers. This allows its -3dB
bandwidth to remain relatively constant as closed-loop gain
is increased. This combination of high bandwidth and low
power, together with aggressive pricing make the EL2270
the ideal choice for many low-power/high-bandwidth
applications such as portable computing, HDSL, and video
processing.
For applications where board space is extremely critical. The
EL2270 is available in industry standard pinouts in SO
package.
For single and dual applications with disable, consider the
EL2176 (8-pin single) and EL2276 (14-pin dual). If higher
speed is required, refer to the EL2180/EL2186 family which
provides singles, duals, triples, and quads with 250MHz of
bandwidth while consuming 3mA of supply current per
amplifier.
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high-frequency device, good printed circuit
board layout is necessary for optimum performance. Ground
plane construction is highly recommended. Lead lengths
should be as short as possible. The power supply pins must
be well bypassed to reduce the risk of oscillation. The
combination of a 4.7µF tantalum capacitor in parallel with a
0.1µF capacitor has been shown to work well when placed at
each supply pin.
For good AC performance, parasitic capacitance should be
kept to a minimum especially at the inverting input (see the
Capacitance at the Inverting Input section). Ground plane
construction should be used, but it should be removed from
the area near the inverting input to minimize any stray
capacitance at that node. Carbon or Metal-Film resistors are
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 EL2270 has
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 EL2270 has 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 EL2270 is a current-
feedback amplifier, 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 EL2270 is a current-feedback amplifier, its gain-
bandwidth product is not a constant for different closed-loop
gains. This feature actually allows the EL2270 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 EL2270 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 EL2270 will
operate on dual supplies ranging from ±1.5V to ±6V. With a
single-supply, the EL2270 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
EL2270 has an input voltage range that extends to within 1V
of either supply. So, for example, on a single +5V supply, the
EL2270 has an input range which spans from 1V to 4V. The
output range of the EL2270 is also quite large, extending to
within 1V of the supply rail. On a ±5V supply, the output is
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