LMC6484 Datasheet, PDF (23/45 Pages) National Semiconductor (TI) – CMOS Quad Rail-to-Rail Input and Output Operational Amplifier

www.ti.com
7 Detailed Description
LMC6484
SNOS675C – AUGUST 2000 – REVISED SEPTEMBER 2015
7.1 Overview
The LMC6484C is a quad operational amplifier that offers a low cost, low power solution for applications
requiring multiple operational amplifier stages and rail-to-rail operation. It supports a wide supply range (3 V to 15
V) and excellent amplifier-to-amplifer isolation (150 dB typical). It is ideal for battery-powered signal acquisition
systems requiring highly integrated solutions to achieve efficient layout.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Amplifier Topology
The LMC6484 incorporates specially designed wide-compliance range current mirrors and the body effect to
extend input common-mode range to each supply rail. Complementary paralleled differential input stages, like the
type used in other CMOS and bipolar rail-to-rail input amplifiers, were not used because of their inherent
accuracy problems due to CMRR, crossover distortion, and open-loop gain variation.
The input stage design of the LMC6484 is complemented by an output stage capable of rail-to-rail output swing
even when driving a large load. Rail-to-rail output swing is obtained by taking the output directly from the internal
integrator instead of an output buffer stage.
7.3.2 Input Common-Mode Voltage Range
Unlike Bi-FET amplifier designs, the LMC6484 does not exhibit phase inversion when an input voltage exceeds
the negative supply voltage. Figure 46 shows an input voltage exceeding both supplies with no resulting phase
inversion on the output.
Figure 45. An Input Voltage Signal Exceeds the LMC6484
Power Supply Voltages With No Output Phase Inversion
The absolute maximum input voltage is 300 mV beyond either supply rail at room temperature. Voltages greatly
exceeding this absolute maximum rating, as in Figure 46, can cause excessive current to flow in or out of the
input pins possibly affecting reliability.
Copyright © 2000–2015, Texas Instruments Incorporated
Product Folder Links: LMC6484
Submit Documentation Feedback
23