Datasheet

LM6181
SNOS634B –MAY 1998–REVISED MAY 2013 www.ti.com
SLEW RATE CONSIDERATIONS
The slew rate characteristics of current feedback amplifiers are different than traditional voltage feedback
amplifiers. In voltage feedback amplifiers slew rate limiting or non-linear amplifier behavior is dominated by the
finite availability of the 1st stage tail current charging the compensation capacitor. The slew rate of current
feedback amplifiers, in contrast, is not constant. Transient current at the inverting input determines slew rate for
both inverting and non-inverting gains. The non-inverting configuration slew rate is also determined by input
stage limitations. Accordingly, variations of slew rates occur for different circuit topologies.
DRIVING CAPACITIVE LOADS
The LM6181 can drive significantly larger capacitive loads than many current feedback amplifiers. Although the
LM6181 can directly drive as much as 100 pF without oscillating, the resulting response will be a function of the
feedback resistor value. Figure 84 illustrates the small-signal pulse response of the LM6181 while driving a 50 pF
load. Ringing persists for approximately 70 ns. To achieve pulse responses with less ringing either the feedback
resistor can be increased (see typical curves Suggested R
f
and R
s
for C
L
), or resistive isolation can be used
(10Ω–51Ω typically works well). Either technique, however, results in lowering the system bandwidth.
Figure 86 illustrates the improvement obtained with using a 47Ω isolation resistor.
Figure 83.
Figure 84. A
V
= −1, LM6181 Can Directly
Drive 50 pF of Load Capacitance with 70 ns
of Ringing Resulting in Pulse Response
26 Submit Documentation Feedback Copyright © 1998–2013, Texas Instruments Incorporated
Product Folder Links: LM6181