EL2386 查看數據表（PDF） - Renesas Electronics
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EL2386 Datasheet PDF : 13 Pages
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EL2386
Applications Information
Product Description
The EL2386 is a current-feedback operational amplifier that
offers a wide -3dB bandwidth of 250MHz, a low supply current
of 3mA per amplifier and the ability to power down to 0mA. It
also features high output current drive. The EL2386 can output
55mA per amplifier. The EL2386 works with supply voltages
ranging from a single 3V to ±6V, and it is also capable of
swinging to within 1V of either supply on the input and the
output. Because of its current-feedback topology, the EL2386
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 EL2386 the
ideal choice for many low-power/high-bandwidth applications
such as portable computing, HDSL, and video processing.
For single and dual applications, consider the EL2186/EL2286.
For single, dual and quad applications without disable,
consider the EL2180, EL2280, or EL2480, all in industry
standard pin outs. The EL2180 also is available in the tiny
SOT-23 package, which is 28% the size of an SO8 package.
For lower power applications where speed is still a concern,
consider the EL2170/EL2176 family which also comes in
similar single, dual and quad configurations with 70MHz of
bandwidth while consuming 1mA 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. Pin 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
single supply operation, where pin 3 (VS-) is connected to the
ground plane, a single 4.7µF tantalum capacitor in parallel with
a 0.1µF ceramic capacitor across pins 14 and 3 will suffice.
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.
FN7155 Rev 1.00
June 24, 2004
Disable/Power-Down
The EL2386 amplifier can be disabled, placing its output in a
high-impedance state. When disabled, the supply current is
reduced to 0mA. The EL2386 is disabled when its ENABLE pin
is floating or pulled up to within 0.5V of the positive supply.
Similarly, the amplifier is enabled by pulling its ENABLE pin at
least 3V below the positive supply. For ±5V supplies, this
means that an EL2386 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 EL2386 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 EL2186 at ±5V, if ENABLE is tied to -5V (rather
than ground) the supply current will increase about 15% to
3.45mA.
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 EL2386 has less
bandwidth than expected. In this case, the inverting input may
have less parasitic capacitance 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 EL2386 has been designed and specified at gains of +1
and +2 with RF = 750. This value of feedback resistor gives
250MHz of -3dB bandwidth at AV = +1 with about 2.5dB of
peaking, and 180MHz of -3dB bandwidth at AV = +2 with about
0.1dB of peaking. Since the EL2386 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 EL2386 is a current-feedback amplifier, its gain-
bandwidth product is not a constant for different closed-loop
gains. This feature actually allows the EL2386 to maintain
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