Analog Devices Inc. AD7718BRU

Overview

AD7718BRU from Analog Devices is a 24-bit Σ-Δ analog-to-digital converter (ADC) with integrated programmable-gain amplifier (PGA), 10-channel pseudo-differential or 5-channel fully differential input capability, factory calibration, and simultaneous 50 Hz/60 Hz rejection - designed for high-precision industrial sensor signal acquisition in smart transmitters and portable instrumentation.

For engineers reviewing the AD7718BRU datasheet, AD7718BRU pinout, AD7718BRU application, or AD7718BRU equivalent, key selection considerations include its 24-bit resolution with up to 18 bits peak-to-peak noise performance at ±2.56 V range, CHOP mode for enhanced offset stability, VREF Select™ for ratiometric/absolute measurement flexibility, and 3-wire SPI/QSPI/MICROWIRE compatibility with Schmitt-triggered SCLK.

Technical Context

The AD7718BRU implements a sigma-delta modulator with on-chip PLL driven by an external 32.768 kHz crystal, generating internal clocks for configurable output data rates from 5.4 Hz (CHOP enabled) to 1.365 kHz (CHOP disabled). Its dual-reference architecture supports independent REFIN1 and REFIN2 inputs, enabling flexible ratiometric or absolute measurements.

It integrates rail-to-rail input buffers, a 2-bit digital I/O port, and serial interface logic supporting unipolar/bipolar coding. The device operates from independent 3 V or 5 V analog (AVDD) and digital (DVDD) supplies, with power-down current as low as 1 µA on AVDD and 2–30 µA on DVDD depending on oscillator state.

Key Specifications

Pinout & Package

The AD7718BRU is housed in a 28-lead TSSOP package (RU-28), 4.4 mm × 9.7 mm body, 0.65 mm pitch, exposed pad optional for thermal enhancement.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7708BRU, the AD7718BRU delivers 8 additional effective bits and superior 50/60 Hz rejection for demanding sensor applications; versus ADS1256IDBT, it offers superior noise immunity in AC-line environments but requires external timing and more complex configuration for dual-reference use cases.

Availability

AD7718BRU is available at Aetrix Electronics and suitable for industrial process control, smart transmitter design, and portable instrumentation requiring stable component supply, long-lifecycle assurance, and traceable sourcing for safety-critical deployments.

Supply support for AD7718BRU 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, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Wilmington, MA.

The AD7718BRU belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for low-frequency, high-accuracy industrial and instrumentation signal chains where noise, drift, and power efficiency are critical.

FAQ

What is the maximum achievable peak-to-peak resolution of the AD7718BRU under typical operating conditions?

The AD7718BRU achieves up to 18 bits peak-to-peak resolution at ±2.56 V input range with CHOP mode enabled and 20 Hz output data rate. This value is confirmed in the AD7718 specifications table (Rev. 0, page 4) and reflects effective noise-free code resolution after internal filtering and averaging - a key metric for stable DC measurement applications such as precision weigh scales or temperature monitoring using the AD7718BRU.

Does the AD7718BRU require an external crystal, and what is its function?

Yes, the AD7718BRU requires an external 32.768 kHz crystal connected to XTAL1/XTAL2 pins. This crystal feeds an on-chip PLL that generates the precise high-frequency clock needed for the sigma-delta modulator and digital filter. The crystal-based timing ensures exceptional 50 Hz and 60 Hz rejection performance - a defining feature of the AD7718BRU not achievable with RC oscillators.

How does the VREF Select™ feature work in the AD7718BRU, and why is it valuable?

VREF Select™ allows the AD7718BRU to accept either ratiometric references (e.g., sensor excitation voltage applied to REFIN) or absolute precision references (e.g., 2.5 V bandgap) on the same pins. This eliminates the need for external multiplexing or separate reference paths. In smart transmitters using the AD7718BRU, it enables seamless switching between bridge sensors (ratiometric) and RTDs (absolute) within one hardware design.

Can the AD7718BRU operate from a single 3.3 V supply, and how is power distributed?

Yes, the AD7718BRU supports single 3.3 V operation: AVDD = 3.3 V and DVDD = 3.3 V. Its dual-supply architecture allows independent biasing - for example, AVDD can be a clean 3.3 V LDO while DVDD runs from a switched 3.3 V rail. Total typical current is 1.28 mA at 3 V, with analog section drawing ~0.85 mA and digital ~0.43 mA - a key efficiency advantage of the AD7718BRU in low-power systems.

What is the purpose of the P1 and P2 pins on the AD7718BRU, and how are they configured?

P1 and P2 are a 2-bit digital I/O port whose direction and state are controlled via the I/O Control Register. They are referenced to AVDD/AGND (not DVDD), making them suitable for driving analog-domain indicators or interfacing with external analog switches. In the AD7718BRU, these pins provide flexible system-level control without requiring additional GPIO expanders - especially useful in space-constrained smart transmitter PCB layouts.