Beschreibung

The LMC6482 and LMC6484 (LMC648x) devices provide a common-mode range that extends to both supply rails. This rail-to-rail performance combined with excellent accuracy, due to a high CMRR, makes these devices unique among rail-to-rail input amplifiers. The devices are an excellent choice for systems that require a large input signal range, such as data acquisition. The LMC648x are also an excellent upgrade for circuits using limited commonmode range amplifiers, such as the TLC272, TLC274, TLC277 and TLC279.
Maximum dynamic signal range is provided in low voltage and single supply systems by the rail-to-rail output swing of the LMC648x. The rail-to-rail output swing is maintained for loads down to 600Ω of the device. Specified low-voltage characteristics and lowpower dissipation make the LMC648x a great choice for battery-operated systems.
The LMC648x devices are available in PDIP, SOIC, and VSSOP packages.

 

Eigenschaften

• Rail-to-rail input common-mode voltage range (specified over temperature)
• Rail-to-rail output swing (within 20mV of supply rail, 100kΩ load)
• Specified 3V, 5V, and 15V performance
• Excellent CMRR and PSRR: 82dB
• Ultra-low input current: 20fA
• Specified for 2kΩ and 600Ω loads
• Improved replacement for TLC272, TLC277

 

Anwendungen

• Data acquisition (DAQ)
• Currency counter
• Oscilloscope (DSO)
• Intra-DC interconnect (METRO)
• Macro remote radio unit (RRU)
• Multiparameter patient monitor
• Merchant telecom rectifiers
• Train control and management
• Process analytics (pH, gas, concentration, force, and humidity)
• Three phase UPS

 

Übersicht

The LMC648x are CMOS operational amplifiers that supports both rail-to-rail inputs and outputs. The device operates in both dual-supply mode and single-supply mode.

 

Feature Description

Amplifier Topology

The LMC648x are true rail-to-rail input operational amplifiers with an input common-mode range that extends 300mV beyond either supply rail. When the input common-mode voltage swings to about 3V from the positive rail, some dc specifications, namely offset voltage, can be slightly degraded. The LMC648x incorporate a specially designed input stage to reduce the inherent accuracy problems seen in other rail-to-rail input amplifiers. The LMC648x input stage design is complemented by an output stage capable of rail-to-rail output swing even when driving a large load.

Input Common-Mode Voltage Range

Unlike Bi-FET amplifier designs, the LMC648x do not exhibit phase inversion when an input voltage exceeds the negative supply voltage.
The absolute maximum input voltage is 300mV beyond either supply rail at room temperature. Voltages greatly exceeding this absolute maximum rating, can cause excessive current to flow in or out of the input pins possibly affecting reliability.

Schiene-zu-Schiene-Ausgang

The LMC648x output can swing to within a few hundred millivolts of either supply voltage. Use the specified output swing specifications to calculate an approximate output resistance for different sourcing and sinking conditions. Use the calculated output resistance to estimate the maximum output voltage swing as a function of load.

Upgrading Applications

The LMC648x have industry-standard pin outs to retrofit existing applications. System performance can be greatly increased by the features of the LMC648x. The key benefit of designing in the LMC648x is increased linear signal range. Most op amps have limited input common-mode ranges. Signals that exceed this range generate a nonlinear output response that persists long after the input signal returns to the common-mode range.
Linear signal range is vital in applications such as filters where signal peaking can exceed input common-mode ranges resulting in output phase inversion or severe distortion.

 

Data Acquisition Systems

The LMC648x does not require input signals to be scaled down to meet limited common-mode voltage ranges. The LMC648x CMRR of 82dB maintains integral linearity of a 12-bit data acquisition system to ±0.325 LSB. Other rail-to-rail input amplifiers with only 50dB of CMRR can degrade the accuracy of the data acquisition system to only 8 bits.
The LMC648x have high input impedance, large common-mode range and high CMRR needed for designing instrumentation circuits. Instrumentation circuits designed with the LMC648x can reject a larger range of common-mode signals than most in-amps. This makes instrumentation circuits designed with the LMC648x an excellent choice for noisy or industrial environments. Other applications that benefit from these features include analytic medical instruments, magnetic field detectors, gas detectors, and silicon-based transducers.