LM6182AMN National Semiconductor, LM6182AMN Datasheet - Page 18

• Manufacturer Part Number: LM6182AMN
• Description: Dual 100 mA Output/ 100 MHz Current Feedback Amplifier
• Manufacturer: National Semiconductor

www.national.com
Typical Applications
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 is pro-
portional to the current available to the amplifier’s compen-
sation capacitor. The current feedback amplifier is therefore
not traditionally slew rate limited. This enables large slew
rates responses of 2000 V/µs. The non-inverting configura-
tion slew rate is also determined by input stage limitations.
Accordingly, variations of slew rates occur for different circuit
topologies.
Eliminating Peaking in the Resulting Pulse Response
FIGURE 8. RC Limits Amplifier Bandwidth to 50 MHz,
as Compared to Figure 3A
8A
8B
(Continued)
DS011926-31
DS011926-30
18
DRIVING CAPACITIVE LOADS
The LM6182 can drive significantly larger capacitive loads
than many current feedback amplifiers. This is extremely
valuable for simplifying the design of coax-cable drivers. Al-
though the LM6182 can directly drive as much as 100 pF of
load capacitance without oscillating, the resulting response
will be a function of the feedback resistor value. Figure 9B il-
lustrates the small-signal pulse response of the LM6182
while driving a 50 pF load. Ringing persists for approximately
100 ns. To achieve pulse responses with less ringing either
the feedback resistor can be increased (see Typical Perfor-
mance Characteristics “Suggested R
sistive isolation can be used (10 –51 typically works well).
Either technique, however, results in lowering the system
bandwidth.
Figure 10B illustrates the improvement obtained by using a
47
FIGURE 9. A
Load Capacitance with 100 ns of Ringing Resulting in
isolation resistor.
V
= −1, LM6182 Can Directly Drive 50 pF of
Pulse Response
9A
9B
f
and Rs for C
DS011926-32
DS011926-33
L
”), or re-