DESCRIPTION

The LT1112 dual op amps achieve a new standard in combining low cost and outstanding precision specifications. The performance of the selected prime grades matches or exceeds competitive devices. In the design of the LT1112 however, particular emphasis has been placed on optimizing performance in the low cost plastic and SO packages. For example, the 75µV maximum offset voltage in these low cost packages is the lowest on any dual or quad non-chopper op amp. The LT1112 also provide a full set of matching specifications, facilitating their use in such matching dependent applications as two and three op amp instrumentation amplifiers. Another set of specifications is furnished at ±1V supplies. This, combined with the low 320µA supply current per amplifier, allows the LT1112 to be powered by two nearly discharged AA cells.

FEATURES

Offset Voltage – Prime Grade: 60µV Max

Offset Voltage – Low Cost Grade (Including Surface Mount Dual/Quad): 75µV Max

Offset Voltage Drift: 0.5µV/°C Max

Input Bias Current: 250pA Max

0.1Hz to 10Hz Noise: 0.3µVP-P, 2.2pAP-P

Supply Current per Amplifier: 400µA Max

CMRR: 120dB Min

Voltage Gain: 1 Million Min

Guaranteed Specs with ±1.0V Supplies

Guaranteed Matching Specifications

SO-8 Package – Standard Pinout

APPLICATIONS

Picoampere/Microvolt Instrumentation

Two and Three Op Amp Instrumentation Amplifers

Thermocouple and Bridge Amplifiers

Low Frequency Active Filters

Photo Current Amplifiers

Battery-Powered Systems

APPLICATIONS IFORMATION

The LT1112 dual  in the plastic and ceramic DIP packages are pin compatible to and directly replace such precision op amps as the OP-200, OP-297, AD706 duals and OP-400, OP-497, AD704 quads with improved price/performance. The LT1112 in the S8 surface mount package has the standard pin configuration, i.e., the same configuration as the plastic and ceramic DIP packages. All competitors are in the wide 16-pin package which occupies 1.8 times the area of the narrow package. The wide package is also 1.8 times thicker than the narrow package. The inputs of the LT1112 are protected with back-toback diodes. In the voltage follower configuration, when the input is driven by a fast large-signal pulse (>1V), the input protection diodes effectively short the output to the input during slewing, and a current, limited only by the output short-circuit protection, will flow through the diodes. The use of a feedback resistor is recommended because this resistor keeps the current below the short-circuit limit, resulting in faster recovery and settling of the output. The input voltage of the LT1112 should never exceed the supply voltages by more than a diode drop. However, the example below shows that as the input voltage exceeds the common mode range, the LT1112’s  output clips cleanly, without any glitches or phase reversal. The OP-297 exhibits phase reversal. The photos also illustrate that both the input and output ranges of the LT1112 are within 800mV of the supplies. The effect of input and output overdrive on the other amplifiers in the LT1112  packages is negligible, as each amplifier is biased independently.

Advantages of Matched Dual and Quad Op Amps

In many applications the performance of a system depends on the matching between two operational amplifiers rather than the individual characteristics of the two op amps. Two or three op amp instrumentation amplifiers, tracking voltage references and low drift active filters are some of the circuits requiring matching between two op amps. The well-known triple op amp configuration illustrates these concepts. Output offset is a function of the difference between the offsets of the two halves of the LT1112. This error cancellation principle holds for a considerable number of input referred parameters in addition to offset voltage and its drift with temperature. Input bias current will be the average of the two noninverting input currents (IB+). The difference between these two currents (∆IB+) is the offset current of the instrumentation amplifier. Common mode and power supply rejections will be dependent only on the match between the two amplifiers (assuming perfect resistor matching).