Analog Devices Inc. AD694ARZ

Overview

AD694ARZ from Analog Devices is a monolithic 4–20 mA current transmitter IC designed for industrial process control signal conditioning. It accepts precalibrated 0 V to 2 V or 0 V to 10 V single-ended inputs, integrates a precision 2.000 V/10.000 V voltage reference, delivers 4–20 mA output with ±0.005% typical nonlinearity, and operates from 4.5 V to 36 V supply across –40°C to +85°C. It drives valves, actuators, and sensor transmitters in noisy plant environments.

For engineers reviewing the AD694ARZ datasheet, AD694ARZ pinout, AD694ARZ application, or AD694ARZ equivalent, key selection criteria include input span programmability (2 V/10 V), output compliance (within 2 V of VS), open-loop alarm capability (Pin 10), 4 mA on/off control (Pin 9), and compatibility with 8-/10-/12-bit DACs - all critical for loop-powered field instrumentation design.

Technical Context

The AD694ARZ implements a three-stage architecture: a PNP-input buffer amplifier (Pin 2/3 → Pin 1 FB) with rail-to-rail common-mode range, a voltage-to-current (V/I) converter using current mirroring and Darlington-level shifting to achieve high compliance, and a laser-trimmed voltage reference with selectable 2 V/10 V outputs (Pins 7/8). Its output stage supports dual-supply operation with IOUT sinking below COM by up to 36 V.

Pin-strapping configures core functions: Pin 4 shorted to COM selects 2 V full-scale input; Pins 7/8 shorted selects 2 V reference; Pin 9 ≥3.0 V disables 4 mA offset for 0–20 mA mode; Pin 10 provides open-collector alarm for loop-open or output noncompliance detection. The internal 4 mA offset generator sums with the 0–16 mA signal current at Pin 14 (BW ADJUST).

Key Specifications

Pinout & Package

AD694ARZ is housed in a 16-pin plastic SOIC package (body width 7.5 mm, lead pitch 1.27 mm), RoHS-compliant, rated for industrial temperature operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4–20 mA transmitter applications.

Compared with AD694ARZ, XTR115UA offers lower power but less configurability, while MAX1637EAP+ simplifies BOM with integrated regulation yet sacrifices precision and diagnostic features - AD694ARZ remains optimal where programmable spans, high accuracy, and robust diagnostics are mandatory.

Availability

AD694ARZ is available at Aetrix Electronics and suitable for industrial process control, factory automation, and sensor transmitter designs requiring stable component supply, long-term lifecycle continuity, and guaranteed industrial temperature performance.

Supply support for AD694ARZ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, founded in 1965 and headquartered in Wilmington, MA.

The AD694ARZ belongs to Analog Devices' precision signal conditioning product line, engineered specifically for noise-immune 4–20 mA current loop transmission in harsh industrial environments.

FAQ

What input voltage ranges does the AD694ARZ support without external resistors?

The AD694ARZ supports two precalibrated input ranges without external components: 0 V to 2 V (selected by shorting Pin 4 to Pin 5) and 0 V to 10 V (selected by leaving Pin 4 open). Both ranges are laser-trimmed at wafer level for ±0.005% nonlinearity. Other spans require external resistor networks per the "Programming Other Spans" section of the datasheet. The AD694ARZ buffer amplifier's PNP input stage accepts signals down to –0.3 V relative to COM, enabling direct connection to many sensor outputs.

How does the AD694ARZ achieve output compliance below common in dual-supply configurations?

The AD694ARZ uses a unique output stage topology where the IOUT pin (Pin 11) is driven by a Darlington-based current source referenced to VS, not COM. This allows the output voltage to swing as low as 36 V below VS - e.g., to –23.5 V when VS = +12.5 V - independent of the substrate potential. Only Pin 11 is permitted to go below COM; all other pins must remain ≥ COM to avoid latch-up. This architecture eliminates level-shifting requirements when interfacing with dual-supply DACs.

Can the AD694ARZ operate from a 5 V supply, and what limitations apply?

Yes, the AD694ARZ can operate from a 5 V supply, but only in 2 V full-scale input mode with the 2 V voltage reference enabled (Pins 7 and 8 shorted). At 5 V, the output compliance is limited to 3 V (VS – 2 V), restricting maximum loop resistance to 150 Ω for 20 mA. The 10 V reference and 10 V input span require ≥12.5 V supply. Quiescent current remains ≤2.0 mA, and all specifications including nonlinearity and reference accuracy are maintained across the –40°C to +85°C range.

What is the function of Pin 9 (4mA ON/OFF) beyond enabling 0–20 mA mode?

Pin 9 serves as a TTL-compatible "jiggle pin" that temporarily disables the 4 mA offset current without affecting the 0–16 mA signal current. This allows brief current interruption (e.g., pulsing 0–20 mA) to unstick mechanically bound valves or actuators. It also enables complete loop shutdown for maintenance. When Pin 9 is pulled ≥3.0 V, the AD694ARZ outputs only the scaled signal current - preserving linearity and bandwidth while removing the DC offset. The AD694ARZ retains full diagnostic capability (e.g., ALARM pin) during this mode.

How is the open-collector ALARM pin (Pin 10) used in system-level fault detection?

Pin 10 asserts a low-state signal when either the 4–20 mA loop opens (e.g., broken wire) or the output voltage at IOUT exceeds VS – 2 V (indicating load overvoltage or saturation). It sinks up to 20 mA and interfaces directly with PLC digital inputs or microcontroller GPIOs. No external pull-up is required if driving a logic input with internal pull-up; otherwise, a 10 kΩ pull-up to VS is recommended. The AD694ARZ alarm circuit is active in both 4–20 mA and 0–20 mA modes, providing continuous loop health monitoring independent of offset configuration.