EL2008C 查看數據表（PDF） - Elantec -> Intersil
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EL2008C Datasheet PDF : 12 Pages
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EL2008C
55 MHz 1 Amp Buffer Amplifier
below shows an example of an EL2008C driving a 100
pF load.
frequency compensation is required. An op amp fol-
lowed with the EL2008C can drive loads as low as 10Ω
to ±10V.
Driving capacitive loads with any closed loop system
creates special problems. The open loop output imped-
ance works into the load capacitance to generate phase
lag which can make the loop unstable. The EL2008C
output impedance is less than 10Ω from DC to 30 MHz.
But a capacitive load of 1000 pF will generate about 45
degrees of phase shift at 30 MHz. More capacitance will
cause the problem at lower frequency.
With enough capacitance even slow op amps will
become unstable. The simplest way to drive capacitive
loads is to isolate them from the feedback with a series
resistor. 1Ω to 5Ω is usually enough but the final value
will depend on the op amp used and the range of load
capacitance.
Driving a pure capacitive load. Top trace is without a snubber.
Bottom trace is with a snubber circuit.
Inductive Loads
The EL2008C with its 1A output current can drive small
motors and other inductive loads. The EL2008C's cur-
rent limiting into inductive loads does NOT in and of
itself cause spikes and kickbacks. However, if the
EL2008C is in current limit and the input voltage is
changing very quickly (i.e., a squarewave) the inductive
load can kick the output beyond the supply voltages.
Motors are also able to generate kickback voltages when
the EL2008C is in current limit.
To prevent damage to the EL2008C when the output
kicks beyond the supplies it is recommended that catch
diodes be placed from each supply to the output.
Op Amp Booster
The EL2008C can boost the output drive of almost any
monolithic op amp. If the phase shift in the EL2008C is
low at the op amp's unity gain frequency, no additional
CL
13 pF
470 pF
1000 pF
3300 pF
0.1 µF
1 µF
5 µF
tr
O.S.
45 ns
20%
50 ns
20%
55 ns
30%
60 ns
30%
350 ns
0%
4 µs
0%
20 µs
0%
Unfortunately the isolation resistor is not inside the op
amp feedback loop and cannot be neglected when com-
puting the DC voltage gain into a resistive load. If load
dependent DC gain is not tolerable then additional high
frequency feedback from the op amp output (the
EL2008C input) and an isolation resistor from the buffer
output can be used to stabilize the loop. This configura-
tion requires the op amp to be unity gain stable. This
feedback method will allow the EL2008C to boost the
output of the EHA2505 amplifier below and serve as a
8
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