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AD694 Datasheet(PDF) 5 Page - Analog Devices |
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AD694 Datasheet(HTML) 5 Page - Analog Devices |
5 / 16 page AD694 REV. B –5– Table I. Precalibrated Ranges for the AD694 Input Output Voltage Min Range Range Reference VS Pin 9 Pin 4 Pin 8 0–2 V 4–20 mA 2 V 4.5 V Pin 5 Pin 5 Pin 7 0–10 V 4–20 mA 2 V 12.5 V Pin 5 Open Pin 7 0–2.5 V 0–20 mA 2 V 5.0 V ≥3 V Pin 5 Pin 7 0–12.5 V 0–20 mA 2 V 15.0 V ≥3 V Open Pin 7 0–2 V 4–20 mA 10 V 12.5 V Pin 5 Pin 5 Open 0–10 V 4–20 mA 10 V 12.5 V Pin 5 Open Open 0–2.5 V 0–20 mA 10 V 12.5 V ≥3 V Pin 5 Open 0–12.5 V 0–20 mA 10 V 15.0 V ≥3 V Open Open BASIC CONNECTIONS: 12.5 V SINGLE-SUPPLY OPERATION WITH 10 V FS Figure 2 shows the minimal connections required for basic operation with a 12.5 V power supply, 10 V input span, 4–20 mA output span, and a 10 V voltage reference. The buffer amplifier is connected as a voltage follower to drive the V/I converter by connecting FB (Pin 1) to –Sig (Pin 2). 4 mA On/ Off (Pin 9) is tied to ground (Pin 5) to enable the 4 mA offset current. The AD694 can drive a maximum load RL = [VS – 2 V] /20 mA, thus the maximum load with a 12.5 V supply is 525 Ω. SELECTING A 2 V FULL-SCALE INPUT The 2 V full-scale option is selected by shorting Pin 4 (2 V FS) to Pin 5 (Common). The connection should be as short as pos- sible; any parasitic resistance will affect the precalibrated span accuracy. SELECTING THE 2 V VOLTAGE REFERENCE The voltage reference is set to a 2 V output by shorting Pin 7 to Pin 8 (10 V Force to 2 V Sense). If desired, the 2 V reference can be set up for remote force and sense connection. Keep in mind that the 2 V Sense line carries a constant current of 100 µA that could cause an offset error over long wire runs. The 2 V reference option can be used with all supply voltages greater than 4.5 V. optional NPN pass transistor can be added to transfer most of the power dissipation off-chip, to extend the temperature range of operation. The output stage is current-limited at approximately 38 mA to protect the output from an overdrive at its inputs. The V/I will allow linear operation to approximately 24 mA. The V/I con- verter also has an open collector alarm (Pin 10) which warns of open-circuit condition at the IOUT pin or of attempts to drive the output to a voltage greater than VS – 2 V. 4 mA OFFSET GENERATOR This circuit converts a constant voltage from the voltage reference to a constant current of approximately 200 µA. This current is summed with the signal current at Pin 14 (BW Adjust), to result in a constant 4 mA offset current at IOUT. The 4 mA Adj (Pin 6) allows the offset current to be adjusted to any current in the range of 2 mA to 4.8 mA. Pin 9 (4 mA On/Off) can shut off the offset current completely if it is lifted to 3.0 V or more, allowing 0 to 20 mA operation of the AD694. In normal 4–20 mA operation, Pin 9 is connected to ground. VOLTAGE REFERENCE A 2 V or 10 V voltage reference is available for user applications, selectable by pin-strapping. The 10 V option is available for supply voltages greater than 12.5 V, the 2 V output is available over the whole 4.5 V to 36 V power supply range. The reference can source up to 5 mA for user applications. A boost transistor can be added to increase the current drive capability of the 2 V mode. APPLYING THE AD694 The AD694 can easily be connected for either dual or single supply operation, to operate from supplies as low as 4.5 V and as high as 36 V. The following sections describe the different connection configurations, as well as adjustment methods. Table I shows possible connection options. Figure 2. Minimal Connections for 0 V to 10 V Single-Ended Input, 4–20 mA Output, 10 V Reference Output |
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