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.
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
Power Supplies
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 100kW 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 1kW 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.
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.
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.
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.
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.
The input characteristics also change when the input
voltage exceeds either supply by 0.5V. This happens
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