Analog Devices Inc. AD7731BNZ

Overview

AD7731BNZ from Analog Devices is a 24-bit sigma-delta analog-to-digital converter optimized for high-precision process control front ends. It integrates a programmable gain amplifier (PGA), buffered differential inputs, a programmable digital filter, and self/system calibration logic. With 16-bit peak-to-peak resolution at 800 Hz, ±20 mV to ±1.28 V bipolar input ranges, and <5 nV/°C offset drift, it directly digitizes low-level transducer signals in industrial PLCs and instrumentation.

For engineers reviewing the AD7731BNZ datasheet, AD7731BNZ pinout, AD7731BNZ application, or AD7731BNZ equivalent, key selection criteria include its 24-bit no-missing-codes performance, FASTStep™ channel sequencing mode, 1 ms settling between six analog input channels, single +5 V analog supply operation, and SPI-compatible three-wire serial interface compatibility with microcontrollers and DSPs.

Technical Context

The AD7731BNZ employs a two-stage digital filter architecture: a configurable SINC³ modulator output stage followed by either a 22-tap FIR filter (normal mode) or a FASTStep™ adaptive filter for rapid step response. Its on-chip PGA supports seven unipolar and seven bipolar input ranges, enabling direct connection to strain gauges, RTDs, and load cells without external signal conditioning.

Chopping (CHP = 1) reduces offset drift to 5 nV/°C and enables 24-bit no-missing-codes performance across –40°C to +85°C. The device features dual calibration modes-self-calibration for factory-trimmed offset/gain correction and system calibration for end-of-line compensation-and includes transducer burnout detection via 100 nA current sources on AIN1(±).

Key Specifications

Pinout & Package

AD7731BNZ is housed in a 24-lead plastic DIP (PDIP) package with 0.3-inch body width and through-hole mounting. Pin 1 is located at the top-left corner when viewed from the top with the notch oriented left.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7731BNZ, AD7190BRUZ delivers superior resolution and drift performance but sacrifices channel sequencing speed and increases power; ADS1258IPWR offers higher throughput and smaller footprint but shifts design burden to external signal conditioning and fault detection circuitry.

Availability

AD7731BNZ is available at Aetrix Electronics and suitable for industrial PLCs, load cell instrumentation, RTD temperature transmitters, and process analyzer sensor interfaces requiring stable component supply across extended product lifecycles.

Supply support for AD7731BNZ 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, serving industrial, automotive, communications, and healthcare markets since 1965.

The AD7731BNZ belongs to Analog Devices' precision sigma-delta ADC product line, designed specifically for ruggedized process control and industrial measurement applications demanding low drift, integrated diagnostics, and simplified analog front-end design.

FAQ

What is the maximum output data rate supported by the AD7731BNZ?

The AD7731BNZ supports programmable output rates up to 6.4 kHz in normal mode. At this rate, peak-to-peak resolution decreases to approximately 12 bits, while maintaining 24-bit no-missing-codes performance. For highest resolution, 16-bit p-p is achieved at 800 Hz. The device's FASTStep™ mode enables rapid settling between channels without sacrificing accuracy at intermediate rates.

Does the AD7731BNZ require an external crystal or can it operate with an external clock?

Yes, the AD7731BNZ supports both configurations: a crystal or ceramic resonator can be connected between MCLK IN and MCLK OUT, or a CMOS-compatible external clock (1–5 MHz) can be applied directly to MCLK IN with MCLK OUT left unconnected. The device is specified for optimal performance at 4.9152 MHz, and MCLK OUT provides an inverted clock output capable of driving one CMOS load when used with an external clock source.

How does the transducer burnout detection function work on the AD7731BNZ?

The AD7731BNZ integrates matched ±100 nA current sources on AIN1(+) and AIN1(–). When enabled, these sources inject current into the connected transducer; an open circuit causes a detectable voltage shift at the input pins, triggering diagnostic flags in the status register. This eliminates the need for external burnout resistors or comparators, simplifying PCB layout and improving reliability in harsh environments.

Can the AD7731BNZ operate from a single 3.3 V supply?

No-the AD7731BNZ requires separate analog and digital supplies: AVDD must be +5 V (±5%), while DVDD accepts +2.7 V to +5.25 V. Operating AVDD at 3.3 V violates the absolute maximum rating and will result in undefined behavior or damage. However, DVDD may be supplied at 3.3 V to interface with 3.3 V logic systems, provided AVDD remains at +5 V.

What is the purpose of the SKIP bit in the AD7731BNZ digital filter configuration?

The SKIP bit disables the second-stage 22-tap FIR filter, leaving only the SINC³ modulator output stage active. This reduces group delay and increases effective output rate-useful for applications requiring faster response to transient events-but at the cost of reduced noise rejection and increased out-of-band aliasing. SKIP mode is typically used in conjunction with FASTStep™ for optimized step-response performance.