LM6171 datasheet(12/17 Pages) NSC

12 / 17 page

Typical Performance Characteristics Unless otherwise noted, T

A = 25˚C (Continued)

LM6171 Simplified Schematic

Application Information

LM6171 Performance Discussion

The LM6171 is a high speed, unity-gain stable voltage feed-

back amplifier. It consumes only 2.5 mA supply current while

providing a gain-bandwidth product of 100 MHz and a slew

rate of 3600V/µs. It also has other great features such as low

differential gain and phase and high output current. The

LM6171 is a good choice in high speed circuits.

The LM6171 is a true voltage feedback amplifier. Unlike cur-

rent feedback amplifiers (CFAs) with a low inverting input im-

pedance and a high non-inverting input impedance, both in-

puts of voltage feedback amplifiers (VFAs) have high

impedance nodes. The low impedance inverting input in

CFAs will couple with feedback capacitor and cause oscilla-

tion. As a result, CFAs cannot be used in traditional op amp

circuits such as photodiode amplifiers, I-to-V converters and

integrators.

LM6171 Circuit Operation

The class AB input stage in LM6171 is fully symmetrical and

has a similar slewing characteristic to the current feedback

amplifiers. In the LM6171 Simplfied Schematic, Q1 through

Q4 form the equivalent of the current feedback input buffer,

E the equivalent of the feedback resistor, and stage A buff-

ers the inverting input. The triple-buffered output stage iso-

lates the gain stage from the load to provide low output im-

pedance.

LM6171 Slew Rate Characteristic

The slew rate of LM6171 is determined by the current avail-

able to charge and discharge an internal high impedance

node capacitor. The current is the differential input voltage

divided by the total degeneration resistor R

E. Therefore, the

Undistorted Output Swing

vs Frequency

DS012336-71

Undistorted Output Swing

vs Frequency

DS012336-72

Total Power

Dissipation vs

Ambient Temperature

DS012336-73

DS012336-10

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