5

Burn-In Circuit

Simplified Schematic

Application Information

The EL2001 is a monolithic buffer amplifier built on Elantec's

proprietary dielectric isolation process that produces NPN

and PNP transistors with essentially identical DC and AC

characteristics. The EL2001 takes full advantage of the

complementary process with a unique circuit topology.

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 2000V/µs

slew rates with 100

Ω 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 (±5V) and 36V

(±18V). It is not necessary to use equal split value supplies.

For example -5V and +12V would be excellent for signals

from -2V to +9V.

Bypass capacitors from each supply pin to ground are highly

recommended to reduce supply ringing and the interference

it can cause. At a minimum, 1µF tantalum capacitor with

short pins should be used for both supplies.

Input Characteristics

The input to the EL2001 looks like a resistance in parallel

with about 3.5pF in addition to a DC bias current. The DC

bias current is due to the miss-match in beta and collector

current between 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

input range; typical input current curves are shown in the

characteristic curves. Internal clamp diodes 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 ±2.5V input to output differential. When

that happens the input resistance drops dramatically. The

diodes are rated at 50mA. When conducting they have a

series resistance of about 20

Ω. There is also 100Ω in series

with the input that limits input current. Above ±7.5V

differential input to output, additional 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 1Mb present no oscillation problems. Care

must be used in board layout to minimize output to input

coupling. CAUTION: When using high source impedances

output offset, load resistor, and the action of the boost circuit.

See typical performance curves.

Large Signal Response

Small Signal Response

EL2001