Overview
The AD694AQ, produced by Analog Devices Inc., is a monolithic current transmitter designed to convert high-level signal inputs into a standard 4–20 mA current loop. This device is ideal for systems requiring noise-immune signal transmission to operate valves, actuators, and other control devices. It is also suitable for transmitting process parameters such as pressure, temperature, or flow. The AD694AQ is recommended as a replacement for discrete designs in various applications, including industrial process control, factory automation, and system monitoring.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| Input Voltage Range | -0.2 VS | -2.0 V | -2.5 V | V |
| Input Bias Current | 1.5 | 51 | 51 | nA |
| Offset Current | ± 0.1 | ±11 | ±11 | nA |
| Offset Current Drift | ± 1.0 | ± 5.0 | ± 5.0 | pA/°C |
| Input Impedance | 5 | 5 | 5 | MΩ |
| Operating Current Range | 0 | 23 | 23 | mA |
| Specified Performance | 4 | 20 | 20 | mA |
| Output Voltage Compliance | VS – 36 V | VS – 2 V | VS – 36 V | V |
| Output Impedance, 4–20 mA | 40.0 | 50.0 | 50.0 | MΩ |
| Current Limit (@ 2 × FS Overdrive) | 241 | 441 | 441 | mA |
| Slew Rate | 1.3 | 1.3 | 1.3 | mA/µs |
| SPAN AND ZERO ACCURACY | ||||
| 4 mA Offset Error @ 0 V Input | ± 10 | ±201 | ±201 | µA |
| Error from 0.000 mA, 4 mA Off | 0 | ± 10 | ± 10 | µA |
Key Features
- Complete voltage-to-current transmitter with pin-programmable input ranges precalibrated at 0 V to 2 V and 0 V to 10 V.
- The input amplifier can be configured to buffer and scale the input voltage or serve as an output amplifier for current output DACs.
- Output voltage compliance extends to within 2 V of the positive supply and below common.
- Interfaces directly with 8-, 10-, and 12-bit single supply CMOS and bipolar DACs.
- The 4 mA zero current can be switched on and off with a TTL control pin, allowing 0–20 mA operation.
- An open collector alarm warns of loop failure due to open wires or noncompliance of the output stage.
- A monitored output is provided to drive an external pass transistor, off-loading power dissipation to extend the temperature range of operation and minimize self-heating error.
Applications
The AD694AQ is widely used in various industrial and automation applications, including:
- Industrial process control: For the transmission of process parameters such as pressure, temperature, or flow.
- Factory automation: To control valves, actuators, and other control devices.
- System monitoring: To ensure reliable and noise-immune signal transmission.
Q & A
- What is the primary function of the AD694AQ? The AD694AQ is a voltage-to-current transmitter that converts high-level signal inputs into a standard 4–20 mA current loop.
- What are the precalibrated input ranges for the AD694AQ? The input ranges are precalibrated at 0 V to 2 V and 0 V to 10 V.
- How can the input amplifier be configured? The input amplifier can be configured to buffer and scale the input voltage or serve as an output amplifier for current output DACs.
- What is the output voltage compliance of the AD694AQ? The output voltage compliance extends to within 2 V of the positive supply and below common.
- Can the AD694AQ interface with DACs? Yes, it interfaces directly with 8-, 10-, and 12-bit single supply CMOS and bipolar DACs.
- How can the 4 mA zero current be controlled? The 4 mA zero current can be switched on and off with a TTL control pin, allowing 0–20 mA operation.
- What is the purpose of the open collector alarm? The open collector alarm warns of loop failure due to open wires or noncompliance of the output stage.
- How does the monitored output feature work? The monitored output drives an external pass transistor, off-loading power dissipation to extend the temperature range of operation and minimize self-heating error.
- In what temperature range is the AD694AQ specified? The AD694AQ is specified over the –40°C to +85°C industrial temperature range for hermetically sealed and plastic SOIC packages, and 0°C to +70°C for the plastic DIP package.
- What are some common applications of the AD694AQ? It is used in industrial process control, factory automation, and system monitoring.
