Datasheet

LF411-N

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SNOSBH6D –APRIL 1998–REVISED MARCH 2013

The LF411 is biased by a zener reference which allows normal circuit operation on ±4.5V power supplies. Supply

voltages less than these may result in lower gain bandwidth and slew rate.

The LF411 will drive a 2 kΩ load resistance to ±10V over the full temperature range. If the amplifier is forced to

drive heavier load currents, however, an increase in input offset voltage may occur on the negative voltage swing

and finally reach an active current limit on both positive and negative swings.

Precautions should be taken to ensure that the power supply for the integrated circuit never becomes reversed in

polarity or that the unit is not inadvertently installed backwards in a socket as an unlimited current surge through

the resulting forward diode within the IC could cause fusing of the internal conductors and result in a destroyed

unit.

As with most amplifiers, care should be taken with lead dress, component placement and supply decoupling in

order to ensure stability. For example, resistors from the output to an input should be placed with the body close

to the input to minimize “pick-up” and maximize the frequency of the feedback pole by minimizing the

capacitance from the input to ground.

A feedback pole is created when the feedback around any amplifier is resistive. The parallel resistance and

capacitance from the input of the device (usually the inverting input) to AC ground set the frequency of the pole.

In many instances the frequency of this pole is much greater than the expected 3 dB frequency of the closed

loop gain and consequently there is negligible effect on stability margin. However, if the feedback pole is less

than approximately 6 times the expected 3 dB frequency, a lead capacitor should be placed from the output to

the input of the op amp. The value of the added capacitor should be such that the RC time constant of this

capacitor and the resistance it parallels is greater than or equal to the original feedback pole time constant.

TYPICAL APPLICATIONS

PNP=2N2905

NPN=2N2219 unless noted

TO-5 heat sinks for Q6-Q7

Figure 30. High Speed Current Booster

Product Folder Links: LF411-N