EL2001CM datasheet(7/12 Pages) ELANTEC

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EL2001C

Low Power 70 MHz Buffer Amplifier

Burn-In Circuit

2001 – 9

Simplified Schematic

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-

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

Power Supplies

The EL2001 may be operated with single or split

supplies with total voltage difference between

10V (g5V) and 36V (g18V) It is not necessary

to use equal split value supplies For example

5V and a12V would be excellent for signals

from b2V to a9V

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

Input Characteristics

The input to the EL2001 looks like a resistance in

parallel with about 35 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 (RIN) is affected by the out-

put load beta and the internal boost RIN can

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

diodes begin conduction at about g25V 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 20

X There is also 100X in

series with the input that limits input current

Above g75V 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-

pedances (RS l 100 kX) significant gain errors

can be observed due to output offset load resis-

tor and the action of the boost circuit See typi-

cal performance curves

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