EL2276CS 데이터 시트보기 (PDF) - Elantec -> Intersil
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EL2276CS Datasheet PDF : 14 Pages
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EL2176, EL2276
Applications Information
Product Description
The EL2176/EL2276 are current-feedback operational
amplifiers that offer a wide -3dB bandwidth of 70MHz, a low
supply current of 1mA per amplifier and the ability to disable
to 0mA. Both products also feature high output current drive.
The EL2176 can output 100mA, while the EL2276 can
output 55mA per amplifier. The EL2176/EL2276 work with
supply voltages ranging from a single 3V to ±6V, and they
are also capable of swinging to with in 1V of either supply on
the input and the output. Because of their current-feedback
topology, the EL2176/EL2276 do not have the normal gain-
bandwidth product associated with voltage-feedback
operational amplifiers. This allows their -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 EL2176/EL2276 the ideal
choice for many low-power/high-bandwidth applications such
as portable computing, HDSL, and video processing.
For Single, Dual and Quad applications without disable,
consider the EL2170 (8-Pin Single), EL2270 (8-Pin Dual)
and EL2470 (14-Pin Quad). If more AC performance is
required, refer to the EL2180/EL2186 family which provides
Singles, Duals, 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.
Disable/Power-Down
The EL2176/EL2276 amplifiers can be disabled, placing
their output in a high-impedance state. When disabled, each
amplifier's supply current is reduced to 0mA. Each
EL2176/EL2276 amplifier is disabled when its ENABLE pin
is floating or pulled up to within 0.5V of the positive supply.
Similarly, each amplifier is enabled by pulling its ENABLE pin
at least 3V below the positive supply. For ±5V supplies, this
means that an EL2176/EL2276 amplifier will be enabled
when ENABLE is at 2V or less, and disabled when ENABLE
is above 4.5V. Although the logic levels are not standard
TTL, this choice of logic voltages allows the EL2176/EL2276
to be enabled by tying ENABLE to ground, even in +3V
single-supply applications. The ENABLE pin can be driven
from CMOS outputs or open-collector TTL.
When enabled, supply current does vary somewhat with the
voltage applied at ENABLE. For example, with the supply
voltages of the EL2176 at ±5V, if ENABLE is tied to -5V
(rather than ground) the supply current will increase about
15% to 1.15mA.
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 EL2176/EL2276 have been specially designed to
reduce power dissipation in the feedback network by using
large 1.0kΩ feedback and gain resistors. With the high
bandwidths of these amplifiers, these large resistor values
would normally cause stability problems when combined
with parasitic capacitance, but by internally canceling the
effects of a nominal amount of parasitic capacitance, the
EL2176/EL2276 remain very stable. For less experienced
users, this feature makes the EL2176/EL2276 much more
forgiving, and therefore easier to use than other products not
incorporating this proprietary circuitry.
The experienced user with a large amount of PC board
layout experience may find in rare cases that the
EL2176/EL2276 have less bandwidth than expected. In this
case, the inverting input may have less parasitic capacitance
than expected by the internal compensation circuitry of the
EL2176/EL2276. 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
9
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