
EL2180CEL2280CEL2480C
250 MHz3 mA Current Mode Feedback Amplifiers
Applications Information
Product Description
The EL2180CEL2280CEL2480C are current-
feedback operational amplifiers that offer a wide
b
3 dB bandwidth of 250 MHz and a low supply
current of 3 mA per amplifier All of these prod-
ucts also feature high output current drive The
EL2180C can output 100 mA while the EL2280C
and the EL2480C can output 55 mA per amplifi-
er The EL2180CEL2280CEL2480C work with
supply voltages ranging from a single 3V to
g
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 topolo-
gy
the EL2180CEL2280CEL2480C do not
have the normal gain-bandwidth product associ-
ated with voltage-feedback operational amplifi-
ers This allows their b3 dB bandwidth to re-
main relatively constant as closed-loop gain is in-
creased This combination of high bandwidth and
low power together with aggressive pricing make
the
EL2180CEL2280CEL2480C
the
ideal
choice for many low-powerhigh-bandwidth ap-
plications such as portable computing HDSL
and video processing
For applications where board space is extremely
critical the EL2180C is available in the tiny
5-lead SOT23 package
which has a footprint
28% the size of an 8-lead SOIC The EL2180C
EL2280CEL2480C are each also available in in-
dustry standard pinouts in PDIP and SOIC pack-
ages
For Single Dual and Triple applications with
disable
consider the EL2186C (8-Pin Single)
EL2286C (14-Pin Dual) and EL2386C (16-Pin
Triple) If lower power is required refer to the
EL2170CEL2176C family which provides Sin-
gles Duals and Quads with 70 MHz of band-
width while consuming 1 mA 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 high-
ly 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 47
mF tantalum capacitor in
parallel with a 01
mF 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 In-
verting Input section) Ground plane construc-
tion should be used but it should be removed
from the area near the inverting input to mini-
mize 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 Sock-
ets 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 cur-
rent-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 amplifi-
er 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 feed-
back and gain resistors further exacerbates the
problem by further lowering the pole frequency
10