EL2003C, EL2033C
100MHz Video Line Driver
impedance of the EL2003C or EL2033C is less than
10W 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.
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.
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.
Complex Feedback with the Buffer to Drive Capacitive Loads
This works with any unity gain stable OA.
Snubber Circuit (51W 470 pF) is optional.
Op Amp Booster with Capacitive Load
10W is enough isolation and speed
CL
tr
OS
10%
50%
35%
0
is determined by the isolation
resistor and capacitive load time
constant.
10pF
17ns
20ns
30ns
80ns
220ns
1.1µs
2.2µs
470pF
0.001µF
0.005µF
0.01µF
0.05µF
0.1µF
0
0
0
11
ELANTEC [ ELANTEC SEMICONDUCTOR ]
