LM124-N, LM224-N

LM2902-N, LM324-N

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SNOSC16D – MARCH 2000 – REVISED JANUARY 2015

7 Detailed Description

7.1 Overview

The LM124-N series are op amps which operate with only a single power supply voltage, have true-differential

over a wide range of power supply voltage with little change in performance characteristics. At 25°C amplifier

7.2 Functional Block Diagram

7.3 Feature Description

The LM124 provides a compelling balance of performance versus current consumption. The 700

μA of supply

current draw over the wide operating conditions with a 1-MHz gain-bandwidth and temperature compensated

bias currents makes the LM124 an effective solution for large variety of applications. The input offset voltage of 2

mV and offset current of 5 nA, along with the 45n-A bias current across a wide supply voltage means a single

design can be used in a large number of different implementations.

7.4 Device Functional Modes

Large differential input voltages can be easily accommodated and, as input differential voltage protection diodes

are not needed, no large input currents result from large differential input voltages. The differential input voltage

from going negative more than

can be used.

To reduce the power supply drain, the amplifiers have a class A output stage for small signal levels which

converts to class B in a large signal mode. This allows the amplifiers to both source and sink large output

currents. Therefore both NPN and PNP external current boost transistors can be used to extend the power

capability of the basic amplifiers. The output voltage needs to raise approximately 1 diode drop above ground to

bias the on-chip vertical PNP transistor for output current sinking applications.

For ac applications, where the load is capacitively coupled to the output of the amplifier, a resistor should be

used, from the output of the amplifier to ground to increase the class A bias current and prevent crossover

distortion.

Where the load is directly coupled, as in dc applications, there is no crossover distortion.

Capacitive loads which are applied directly to the output of the amplifier reduce the loop stability margin. Values

of 50 pF can be accommodated using the worst-case non-inverting unity gain connection. Large closed loop

gains or resistive isolation should be used if larger load capacitance must be driven by the amplifier.

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Product Folder Links: LM124-N LM224-N LM2902-N LM324-N