EL2386C
250 MHz Triple Current Feedback Amp w Disable
Applications Information
Product Description
The EL2386C is a current-feedback operational
amplifier that offers a wide
b
3 dB bandwidth of
250 MHz a low supply current of 3 mA per am-
plifier and the ability to power down to 0 mA It
also features high output current drive The
EL2386C can output 55 mA per amplifier The
EL2386C works with supply voltages ranging
from a single 3V to
g
6V and it is also capable of
swinging to within 1V of either supply on the
input and the output Because of its current-feed-
back topology the EL2386C does not have the
normal gain-bandwidth product associated with
voltage-feedback operational amplifiers This al-
lows its
b
3 dB 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
EL2386C 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
EL2186C EL2286C For Single Dual and Quad
applications without disable consider the
EL2180C EL2280C or EL2480C all in industry
standard pin outs The EL2180C also is available
in the tiny SOT-23 package which is 28% the
size of an SO8 package For lower power applica-
tions where speed is still a concern consider the
EL2170C EL2176C family which also comes in
similar Single Dual and Quad configurations
with 70 MHz of bandwidth while consuming
1 mA of supply current per amplifier
nected to the ground plane a single 4 7
mF
tanta-
lum capacitor in parallel with a 0 1
mF
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 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
Disable Power-Down
The EL2386C amplifier can be disabled placing
its output in a high-impedance state When dis-
abled the supply current is reduced to 0 mA The
EL2386C is disabled when its ENABLE pin is
floating or pulled up to within 0 5V of the posi-
tive supply Similarly the amplifier is enabled by
pulling its ENABLE pin at least 3V below the
positive supply For
g
5V supplies this means
that an EL2386C amplifier will be enabled when
ENABLE is at 2V or less and disabled when
ENABLE is above 4 5V Although the logic lev-
els are not standard TTL this choice of logic
voltages allows the EL2386C to be enabled by ty-
ing ENABLE to ground even in
a
3V single-
supply applications The ENABLE pin can be
driven from CMOS outputs or open-collector
TTL
When enabled supply current does vary some-
what with the voltage applied at ENABLE For
example with the supply voltages of the
EL2186C at
g
5V if ENABLE is tied to
b
5V
(rather than ground) the supply current will in-
crease about 15% to 3 45 mA
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 4 7
mF
tantalum capacitor in
parallel with a 0 1
mF
capacitor has been shown
to work well when placed at each supply pin For
single supply operation where pin 3 (V
S-
) is con-
9
ELANTEC [ ELANTEC SEMICONDUCTOR ]
