LM6182AMN datasheet(18/24 Pages) NSC

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Typical Applications (Continued)

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.

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

f and Rs for CL”), or re-

sistive isolation can be used (10

Ω–51Ω typically works well).

Either technique, however, results in lowering the system

bandwidth.

Figure 10B illustrates the improvement obtained by using a

Ω isolation resistor.

DS011926-30

DS011926-31

FIGURE 8. RC Limits Amplifier Bandwidth to 50 MHz,

Eliminating Peaking in the Resulting Pulse Response

as Compared to

Figure 3A

DS011926-32

DS011926-33

FIGURE 9. A

V = −1, LM6182 Can Directly Drive 50 pF of

Load Capacitance with 100 ns of Ringing Resulting in

Pulse Response

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