EL2001C
Low Power, 70 MHz Buffer Amplifier
Power Supplies
The EL2001 may be operated with single or split
supplies with total voltage difference between
Burn-In Circuit
g
g
10V ( 5V) and 36V ( 18V). It is not necessary
to use equal split value supplies. For example
b
a
from 2V to 9V.
5V and
b
12V would be excellent for signals
a
Bypass capacitors from each supply pin to
ground are highly recommended to reduce supply
ringing and the interference it can cause. At a
minimum, 1 mF tantalum capacitor with short
leads should be used for both supplies.
2001–9
Simplified Schematic
Input Characteristics
The input to the EL2001 looks like a resistance in
parallel with about 3.5 picofarads in addition to a
DC bias current. The DC bias current is due to
the miss-match in beta and collector current be-
tween the NPN and PNP transistors connected
to the input pin. The bias current can be either
positive or negative. The change in input current
with input voltage (R ) is affected by the out-
can
IN
put load, beta and the internal boost. R
IN
actually appear negative over portions of the in-
put range; typical input current curves are shown
in the characteristic curves. Internal clamp di-
odes from the input to the output are provided.
These diodes protect the transistor base emitter
junctions and limit the boost current during slew
to avoid saturation of internal transistors. The
g
diodes begin conduction at about 2.5V input to
output differential. When that happens the input
resistance drops dramatically. The diodes are rat-
ed at 50 mA. When conducting they have a series
resistance of about 20X. There is also 100X in
series with the input that limits input current.
2001–10
Application Information
The EL2001 is a monolithic buffer amplifier built
on Elantec’s proprietary dielectric isolation pro-
cess that produces NPN and PNP transistors
with essentially identical DC and AC characteris-
tics. The EL2001 takes full advantage of the com-
plementary process with a unique circuit topolo-
gy.
g
Above 7.5V differential input to output, addi-
tional series resistance should be added.
Source Impedance
The EL2001 has good input to output isolation.
When the buffer is not used in a feedback loop,
capactive and resistive sources up to 1 Meg pres-
ent no oscillation problems. Care must be used in
board layout to minimize output to input cou-
pling. CAUTION: When using high source im-
Elantec has applied for two patents based on the
EL2001’s topology. The patents relate to the base
drive and feedback mechanism in the buffer. This
feedback makes 2000 V/ms slew rates with 100X
loads possible with very low supply current.
l
pedances (R
100 kX), significant gain errors
S
can be observed due to output offset, load resis-
tor, and the action of the boost circuit. See typi-
cal performance curves.
7
ELANTEC [ ELANTEC SEMICONDUCTOR ]
