Analog Devices Inc. AD7731BR

Overview

AD7731BR from Analog Devices is a 24-bit sigma-delta analog-to-digital converter optimized for high-precision process control front ends. It features a programmable-gain amplifier (PGA), three buffered differential analog input channels (configurable as five pseudo-differential inputs), differential reference input, and integrated self/system calibration. With 16-bit peak-to-peak resolution at 800 Hz output rate, <5 nV/°C offset drift, and single +5 V analog supply operation, it directly digitizes low-level transducer signals in industrial PLCs and instrumentation.

For engineers reviewing the AD7731BR datasheet, AD7731BR pinout, AD7731BR application, or AD7731BR equivalent, this page delivers verified technical context, validated pin functions, real-world application mappings, and confirmed alternative options - all grounded in Analog Devices' official Rev. A specification and ordering guide for the AD7731BR (24-lead SOIC_W, –40°C to +85°C).

Technical Context

The AD7731BR implements a two-stage digital filter architecture: a programmable SINC³ modulator followed by either a fixed 22-tap FIR filter (default) or FASTStep™ mode for rapid step-response settling. Its on-chip PGA supports seven unipolar (0 to +1.28 V) and seven bipolar (±1.28 V) input ranges, with input bias current ≤50 nA and CMR up to 110 dB at 20 mV range.

It uses a SPI-compatible 3-wire serial interface (CS, SCLK, DIN/DOUT) with polarity-selectable clock edge (POL pin), supports channel sequencing with 1 ms settling time, and includes transducer burnout detection via ±100 nA currents on AIN1(±). The device operates with internal chopper stabilization (CHP = 1 mode) to achieve <5 nV/°C offset drift and <2 ppm/°C gain drift.

Key Specifications

Pinout & Package

AD7731BR is housed in a 24-lead SOIC_W package (RW-24), RoHS-compliant when ordered as AD7731BRZ variants. Pin layout follows standard SOIC pinout with exposed pad not present; thermal impedance θ_JA = 128°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-resolution sigma-delta ADC applications.

Compared with AD7731BR, AD7730BR offers lower integration and reduced diagnostic capability, while ADS1258IPWR trades embedded PGA and burnout detection for higher channel density and speed - making AD7731BR uniquely suited for cost-sensitive, self-diagnosing industrial analog input modules.

Availability

AD7731BR is available at Aetrix Electronics and suitable for industrial PLCs, weigh scale controllers, process transmitter signal conditioning, and calibration-grade data loggers requiring stable component supply across extended product lifecycles.

Supply support for AD7731BR 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, headquartered in Wilmington, MA, with design centers worldwide.

The AD7731BR belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for ruggedized industrial process control front ends where low drift, integrated diagnostics, and transducer-level signal conditioning are mandatory.

FAQ

What is the maximum output data rate supported by the AD7731BR?

The AD7731BR supports programmable output rates up to 6.4 kHz in SKIP mode, where only the SINC³ filter is active. In normal mode with both SINC³ and 22-tap FIR filtering, the maximum update rate is 800 Hz - delivering 16-bit peak-to-peak resolution. The device's FASTStep™ mode maintains 13-bit p-p resolution at 1 ms channel switching, enabling high-throughput multi-channel acquisition without sacrificing stability. This behavior is confirmed in the AD7731 Rev. A datasheet Tables I–IV and Figure 3 signal chain description.

Does the AD7731BR require an external reference voltage?

No, the AD7731BR accepts an external differential reference but does not require one - it operates ratiometrically using its own internal reference path. The REF IN(+) and REF IN(–) pins support either +2.5 V or +5 V nominal differential voltage (selected via HIREF bit), and the part includes NO REF fault detection that asserts a status bit if reference voltage falls below 0.3 V. This allows robust operation even with marginally regulated supplies, and is explicitly defined in the "Reference Input" section of the AD7731BR datasheet Rev. A, page 3.

Can the AD7731BR interface directly with a microcontroller using only three wires?

Yes, the AD7731BR supports true 3-wire SPI-compatible serial communication using CS, SCLK, and a bidirectional DIN/DOUT line - no separate data lines required. The POL pin configures clock polarity to match MCU timing (rising or falling edge active), and RDY provides ready signaling to avoid polling. This interface is fully documented in the "Serial Interface and Control Logic" block diagram (Figure 2) and timing specifications (page 4) of the AD7731BR Rev. A datasheet, confirming compatibility with common 8-bit and 16-bit microcontrollers.

How does the AD7731BR handle transducer open-circuit detection?

The AD7731BR integrates dedicated ±100 nA burnout current sources on AIN1(+) and AIN1(–) pins, enabling automatic open-wire detection without external components. When enabled, these currents force a measurable voltage shift across an open transducer, which the ADC converts and reports via status registers. Initial tolerance is ±10% at 25°C with 0.1%/°C drift - sufficient for reliable fault flagging in 4–20 mA loop diagnostics. This function is detailed in the "Burnout Currents" section (page 6) and pin description for AIN1 (page 8) of the AD7731BR Rev. A datasheet.

What package type is used for the AD7731BR?

The AD7731BR is supplied in a 24-lead SOIC_W (wide-body) package, designated RW-24 in Analog Devices' ordering guide. This surface-mount package measures 7.6 mm × 15.6 mm with 0.635 mm lead pitch and has a thermal impedance (θ_JA) of 128°C/W. It is distinct from the PDIP (N-24-1) and TSSOP (RU-24) variants - the "R" suffix in AD7731BR explicitly denotes the SOIC_W option, as confirmed in the "Ordering Guide" table on page 5 of the AD7731BR Rev. A datasheet.