Datasheet AMP02 (Analog Devices) - 10

AMP02 3 +IN V1 25k
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25k
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SENSE (SOIC-16 ONLY) R 8 RG2 25k
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6 R OUT G R R 1 G1 25k
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25k
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25k
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5 REFERENCE 2 V –IN 2
Figure 4. Triple Op Amp Topology Figure 4 shows the triple op amp configuration of the AMP02.
Grounding
With all instrumentation amplifiers of this type, it is critical not The majority of instruments and data acquisition systems have to exceed the dynamic range of the input amplifiers. The ampli- separate grounds for analog and digital signals. Analog ground may fied differential input signal and the input common-mode volt- also be divided into two or more grounds that will be tied together age must not force the amplifier’s output voltage beyond ± 12 V at one point, usually at the analog power supply ground. In (VS = ± 15 V) or nonlinear operation will result. addition, the digital and analog grounds may be joined—normally at the analog ground pin on the A/D converter. Following this The input stage amplifier’s output voltages at V1 and V2 equal: basic practice is essential for good circuit performance.  2R  VD Mixing grounds causes interactions between digital circuits and the V = – 1 + V 1 R CM 2  G   + analog signals. Since the ground returns have finite resistance and inductance, hundreds of millivolts can be developed between the system ground and the data acquisition components. Using VD = G – + VCM separate ground returns minimizes the current flow in the sensitive 2 analog return path to the system ground point. Consequently, noisy ground currents from logic gates interact with the analog signals.  2R  V V D = 1 + V Inevitably, two or more circuits will be joined together with 2 R CM 2  G   + their grounds at differential potentials. In these situations, the differential input of an instrumentation amplifier, with its high CMR, can accurately transfer analog information from one VD = G + VCM circuit to another. 2
Sense and Reference Terminals
where: The sense terminal completes the feedback path for the instrumen- VD = Differential input voltage tation amplifier output stage and is internally connected directly = (+IN) – (–IN) to the output. For SOIC devices, connect the sense terminal to the output. The output signal is specified with respect to the refer- VCM = Common-mode input voltage ence terminal, which is normally connected to analog ground. G = Gain of instrumentation amplifier The reference may also be used for offset correction level shift- If V ing. A reference source resistance will reduce the common-mode 1 and V2 can equal ± 12 V maximum, the common-mode input voltage range is: rejection by the ratio of 25 kΩ/RREF. If the reference source resis- tance is 1 Ω, the CMR will be reduced 88 dB (25 kΩ/1 Ω = 88 dB).  GV  CMVR 12 V D = ± −  2  REV. E –9– Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE WAFER TEST LIMITS Typical Performance Characteristics APPLICATIONS INFORMATION Input and Output Offset Voltages Input Bias and Offset Currents Gain Common-Mode Rejection Grounding Sense and Reference Terminals Overvoltage Protection Power Supply Considerations OUTLINE DIMENSIONS Revision History