EL2003 INTERSIL [Intersil Corporation], EL2003 Datasheet - Page 8

• Manufacturer Part Number: EL2003
• Description: 100MHz Video Line Driver
• Manufacturer: INTERSIL [Intersil Corporation]

Op Amp Booster
The EL2003 or EL2033 can boost the output drive of almost
any monolithic op amp. Because the phase shift in the
EL2003 and EL2033 is low at the op amp's unity gain
frequency, no additional compensation is required. By
following an op amp with an EL2003 or EL2033, the buffered
op amp can drive cables and other low impedance loads
directly. Even decompensated high speed op amps can take
advantage of the EL2003’s or EL2033’s 100mA drive.
Driving capacitive loads with any closed loop amplifier
creates special problems. The open loop output impedance
works into the load capacitance to generate phase lag which
can make the loop unstable. The output impedance of the
EL2003 or EL2033 is less than 10Ω from DC to about
10MHz, but a capacitive load of 1000pF will generate about
45° phase shift at 10MHz and make high speed op amps
unstable. Obviously more capacitance will cause the same
problem but at lower frequencies, and slower op amps as
well would become unstable.
DOUBLE MATCHED
OP AMP BOOSTER
BACK MATCHED
DIRECT DRIVE
8
EL2003, EL2033
The easiest way to drive capacitive loads is to isolate them
from the feedback with a series resistor. Ten to twenty ohms
is usually enough but the final value depends on the op amp
used and the range of load capacitance.
If the system requirements will not tolerate the isolation
resistor, then additional high frequency feedback from the op
amp output (the buffer input) and an isolating resistor from
the buffer output is required. This requires that the op amp
be unity gain stable.
COMPLEX FEEDBACK WITH THE BUFFER TO DRIVE
CAPACITIVE LOADS
0.001µF
0.005µF
0.01µF
0.05µF
470pF
0.1µF
10pF
This works with any unity gain stable OA.
Snubber Circuit (51Ω 470pF) is optional.
C
10Ω is enough isolation and speed is
determined by the isolation resistor and
capacitive load time constant.
OP AMP BOOSTER WITH CAPACITIVE LOAD
L
220ns
1.1µs
2.2µs
17ns
20ns
30ns
80ns
t
R
10%
50%
35%
OS
0
0
0
0