Datasheet

LM124-N , LM224-N
LM2902-N , LM324-N
www.ti.com 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
inputs, and remain in the linear mode with an input common-mode voltage of 0 V
DC
. These amplifiers operate
over a wide range of power supply voltage with little change in performance characteristics. At 25°C amplifier
operation is possible down to a minimum supply voltage of 2.3 V
DC
.
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
may be larger than V
+
without damaging the device. Protection should be provided to prevent the input voltages
from going negative more than −0.3 V
DC
(at 25°C). An input clamp diode with a resistor to the IC input terminal
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