EL2186C, EL2286C
250MHz/3mA Current Mode Feedback Amp w/Disable
Applications Information
minimize any stray capacitance at that node. Carbon or
Product Description
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 peak-
ing and overshoot.
The EL2186C/EL2286C are current-feedback opera-
tional amplifiers that offer a wide -3dB bandwidth of
250MHz, a low supply current of 3mA per amplifier and
the ability to disable to 0mA. Both products also feature
high output current drive. The EL2186C can output
100mA, while the EL2286C can output 55mA per
amplifier. The EL2186C/EL2286C work with supply
voltages ranging from a single 3V to ±6V, and they are
also capable of swinging to within 1V of either supply
on the input and the output. Because of their current-
feedback topology, the EL2186C/EL2286C 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 EL2186C/EL2286C the ideal choice
for many low-power/high-bandwidth applications such
as portable computing, HDSL, and video processing.
Disable/Power-Down
The EL2186C/EL2286C amplifiers can be disabled,
placing their output in a high-impedance state. When
disabled, each amplifier's supply current is reduced to
0mA. Each EL2186C/EL2286C 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
EL2186C/EL2286C 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
EL2186C/EL2286C 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.
For Single, Dual and Quad applications without disable,
consider the EL2180C (8-Pin Single), EL2280C (8-Pin
Dual) and EL2480C (14-Pin Quad). If lower power is
required, refer to the EL2170C/EL2176C family which
provides Singles, Duals, and Quads with 70MHz of
bandwidth while consuming 1mA of supply current per
amplifier.
When enabled, supply current does vary somewhat with
the voltage applied at ENABLE. For example, with the
supply voltages of the EL2186C at ±5V, if ENABLE is
tied to -5V (rather than ground) the supply current will
increase about 15% to 3.45mA.
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 capac-
itor in parallel with a 0.1µF capacitor has been shown to
work well when placed at each supply pin.
Capacitance at the Inverting Input
Any manufacturer's high-speed voltage- or current-feed-
back 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 capaci-
tance (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
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
same destabilizing effect as a zero in the forward open-
loop response. The use of large value feedback and gain
10
ELANTEC [ ELANTEC SEMICONDUCTOR ]
