EL2150C/EL2157C
125 MHz Single Supply, Clamping Op Amps
Supply Voltage Range and
Single-Supply Operation
The EL2150C/EL2157C have been designed to
operate with supply voltages having a span of
greater than 2.7V, and less than 12V. In practical
terms, this means that the EL2150C/EL2157C
will operate on dual supplies ranging from
Applications Information
Product Description
The EL2150C/EL2157C are the industry’s fastest
single supply operational amplifiers. Connected
b
in voltage follower mode, their 3dB bandwidth
is 125 MHz while maintaining a 275 V/ms slew
rate. With an input and output common mode
range that includes ground, these amplifiers were
optimized for single supply operation, but will
also accept dual supplies. They operate on a total
g
g
6V. With
EL2150C/EL2157C will operate from 2.7V to
1.35V to
a
single-supply, the
a
a
12V. Performance has been optimized for a sin-
a
gle 5V supply.
a
supply voltage range as low as 2.7V or up to
12V. This makes them ideal for 3V applica-
a
a
Pins 7 and 4 are the power supply pins. The posi-
tive power supply is connected to pin 7. When
used in single supply mode, pin 4 is connected to
ground. When used in dual supply mode, the neg-
ative power supply is connected to pin 4.
tions, especially portable computers.
While many amplifiers claim to operate on a sin-
gle supply, and some can sense ground at their
inputs, most fail to truly drive their outputs to
ground. If they do succeed in driving to ground,
the amplifier often saturates, causing distortion
and recovery delays. However, special circuitry
built into the EL2150C/EL2157C allows the out-
put to follow the input signal to ground without
recovery delays.
As supply voltages continue to decrease, it be-
comes necessary to provide input and output
voltage ranges that can get as close as possible to
the supply voltages. The EL2150C/EL2157C
have an input voltage range that includes the
negative supply and extends to within 1.2V of the
Power Supply Bypassing And Printed
Circuit Board Layout
a
positive supply. So, for example, on a single 5V
supply, the EL2150C/EL2157C have an input
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 ceramic capacitor has been
shown to work well when placed at each supply
pin. For single supply operation, where pin 4
range which spans from 0V to 3.8V.
The output range of the EL2150C/EL2157C is
also quite large. It includes the negative rail, and
extends to within 1V of the top supply rail. On a
a
swinging from 0V to 4V. On split supplies, the
5V supply, the output is therefore capable of
a
output will swing 4V. If the load resistor is tied
g
to the negative rail and split supplies are used,
the output range is extended to the negative rail.
(V ) is connected to the ground plane, a single
S
b
4.7 mF tantalum capacitor in parallel with a 0.1
mF ceramic capacitor across pins 7 and 4 will suf-
fice.
Choice Of Feedback Resistor, R
F
The feedback resistor forms a pole with the input
capacitance. As this pole becomes larger, phase
margin is reduced. This increases ringing in the
time domain and peaking in the frequency do-
main. Therefore, R has some maximum value
F
which should not be exceeded for optimum per-
formance. If a large value of R must be used, a
F
small capacitor in the few picofarad range in par-
allel with R can help to reduce this ringing and
F
For good AC performance, parasitic capacitance
should be kept to a minimum. Ground plane con-
struction should be used. Carbon or Metal-Film
resistors are acceptable with the Metal-Film re-
sistors giving slightly less peaking and band-
width because of their additional series induc-
tance. 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 over-
shoot.
peaking at the expense of reducing the band-
width.
12
ELANTEC [ ELANTEC SEMICONDUCTOR ]
