EL2003C datasheet(7/17 Pages) ELANTEC

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EL2003C, EL2033C

100MHz Video Line Driver

Applications Information

The EL2003C and EL2033C are monolithic buffer

amplifiers built with Elantec's proprietary dielectric iso-

lation process that produces NPN and PNP

complimentary transistors. The circuits are connection

of symmetrical common collector transistors that pro-

vide both sink and source current capability independent

of output voltage while maintaining constant output and

input impedances. The high slew rate and wide band-

width of the EL2003C and EL2033C make them useful

beyond video frequencies.

Power Supplies

The EL2003C and EL2033C may be operated with sin-

gle or split supplies as low as ±2.5V (5V total) to as high

as ±18V (36V total). However, the bandwidth, slew rate,

and output impedance degrade significantly for supply

voltages less than ±5V (10V total) as shown in the char-

acteristic curves. It is not necessary to use equal value

split supplies, for example -5V and +12V would be

excellent for 0V to 1V video signals.

Bypass capacitors from each supply pin to a ground

plane are recommended. The EL2003C and EL2033C

will not oscillate even with minimal bypassing, how-

ever, the supply will ring excessively with inadequate

capacitance. To eliminate a supply ringing and the inter-

ference it can cause, a 10µF tantalum capacitor with

short leads is recommended for both supplies. Inade-

quate supply bypassing can also result in lower slew

rates and longer settling times.

Input Range

The input to the EL2003C and EL2033C looks like a

high resistance in parallel with a few picofarads in addi-

tion to a DC bias current. The input characteristics

change very little with output loading, even when the

amplifier is in current limit. However, there are clamp

diodes from the input to the output that protect the tran-

sistor base emitter junctions. These diodes start to

conduct at about ±9.5V input to output differential volt-

age. Of course the input resistance drops dramatically

when the diodes start conducting; the diodes are rated at

±50mA.

The input characteristics also change when the input

voltage exceeds either supply by 0.5V. This happens

because the input transistor's base-collector junctions

forward bias. If the input exceeds the supply by LESS

than 0.5V and then returns to the normal input range, the

output will recover in less than 10ns. However, if the

input exceeds the supply by MORE than 0.5V, the

recovery time can be hundreds of nanoseconds. For this

reason it is recommended that schottky diode clamps

from input to supply be used if a fast recovery from large

input overloads is required.

Source Impedance

The EL2003C and EL2033C have excellent input-output

isolation and are very tolerant of variations in source

impedances. Capacitive sources cause no problems at

all, resistive sources up to 100k

Ω present no problems as

long as care is used in board layout to minimize output

to input coupling. Inductive sources can cause oscilla-

tions; a 1k

Ω resistor in series with the buffer input lead

will usually eliminate problems without sacrificing too

much speed. An unterminated cable or other resonant

source can also cause oscillations. Again, an isolating

resistor will eliminate the problem.

Current Limit

The EL2003C and EL2033C have internal current limits

that protect the output transistors. The current limit goes

down with junction temperature rise as shown in the

characteristic curves. At a junction temperature of

+175°C the current limits are at about 100mA. If the

EL2003C or EL2033C output is shorted to ground when

operating on ±15V supplies, the power dissipation will

be greater than 1.5W. A heat sink is required in order for

the EL2003C or EL2033C to survive an indefinite short.

Recovery time to come out of current limit is about

250ns.

Heat Sinking

When operating the EL2003C and EL2033C in elevated

ambient temperatures and/or high supply voltages and

low impedance loads, the internal power dissipation can

force the junction temperature above the maximum rat-

ing (150°C for the plastic DIP). Also, an indefinite short

of the output to ground will cause excessive power

dissipation.

EL2003C Datasheet(PDF) 7 Page - Elantec Semiconductor

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