AD693

a FEATURES Instrumentation Amplifier Front End Loop-Powered Operation Precalibrated 30 mV or 60 mV Input Spans Independently Adjustable Output Span and Zero Precalibrated Output Spans: 4–20 mA Unipolar 0–20 mA Unipolar 12 ؎ 8 mA Bipolar Precalibrated 100 ⍀ RTD Interface 6.2 V Reference with Up to 3.5 mA of Current Available Uncommitted Auxiliary Amp for Extra Flexibility Optional External Pass Transistor to Reduce Self-Heating Errors Loop-Powered 4–20 mA Sensor Transmitter AD693 FUNCTIONAL BLOCK DIAGRAM PRODUCT DESCRIPTION PRODUCT HIGHLIGHTS The AD693 is a monolithic signal conditioning circuit which accepts low-level inputs from a variety of transducers to control a standard 4–20 mA, two-wire current loop. An on-chip voltage reference and auxiliary amplifier are provided for transducer excitation; up to 3.5 mA of excitation current is available when the device is operated in the loop-powered mode. Alternatively, the device may be locally powered for three-wire applications when 0–20 mA operation is desired. Precalibrated 30 mV and 60 mV input spans may be set by simple pin strapping. Other spans from 1 mV to 100 mV may be realized with the addition of external resistors. The auxiliary amplifier may be used in combination with on-chip voltages to provide six precalibrated ranges for 100 Ω RTDs. Output span and zero are also determined by pin strapping to obtain the standard ranges: 4–20mA, 12 ± 8 mA and 0–20 mA. Active laser trimming of the AD693’s thin-film resistors res...