The XTR117 is a precision current output converter designed to transmit analog 4-20mA signals over an industry-standard current loop. Figure 1 shows basic circuit connections with representative simplified input circuitry. The XTR117 is a two-wire current transmitter. Its input current (pin 2) controls the output current. A portion of the output current flows into the V+ power supply, pin 7. The remaining current flows in Q1. External input circuitry connected to the XTR117 can be powered from VREG. Current drawn from these terminals must be returned to IRET, pin 3. The IRET pin is a local ground for input circuitry driving the XTR117. The XTR117 is a current-input device with a gain of 100. A current flowing into pin 2 produces IO = 100 x IIN. The input voltage at the IIN pin is zero (referred to the IRET pin). A voltage input is converted to an input current with an external input resistor, RIN, as shown in Figure 1. Typical full-scale input voltages range from 1V and upward. Fu...
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