Analog Devices Inc. AD7708BRU

Overview

AD7708BRU from Analog Devices is a 16-bit, 8-/10-channel Σ-Δ analog-to-digital converter optimized for low-frequency industrial measurement. It integrates a programmable gain amplifier (PGA), rail-to-rail input buffers, on-chip 32.768 kHz crystal oscillator with PLL, and 3-wire SPI-compatible serial interface. It operates from single 3 V or 5 V supplies and supports simultaneous 50 Hz/60 Hz rejection - ideal for pressure transducers and smart transmitter front-ends.

For engineers reviewing the AD7708BRU datasheet, AD7708BRU pinout, AD7708BRU application, or AD7708BRU equivalent, key selection criteria include its 16-bit no-missing-codes resolution, CHOP-mode vs. non-CHOP trade-off for noise vs. throughput, VREF Select™ capability for ratiometric/absolute measurements, and pin compatibility with the 24-bit AD7718BRU for scalable system design.

Technical Context

The AD7708BRU implements a sigma-delta modulation architecture with a 2nd-order modulator and digital filter delivering up to 16-bit no-missing-codes performance. Its PGA supports gains of 1 to 128, enabling direct conversion of signals from 20 mV to 2.56 V full-scale without external signal conditioning.

It features dual reference inputs (REFIN1/REFIN2) configurable as analog inputs or reference sources, and supports both unipolar/bipolar coding and chop-enabled (low-drift) or non-chop (higher throughput) operation modes. The device uses separate analog (AVDD/AGND) and digital (DVDD/DGND) supplies for enhanced noise immunity.

Key Specifications

Pinout & Package

The AD7708BRU is housed in a 28-lead TSSOP package (RU-28), with exposed pad for thermal enhancement and compact PCB layout.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ADC applications.

Compared with AD7718BRU and ADS124S08IPW, the AD7708BRU delivers proven 16-bit precision with unique VREF Select™ and dual-reference configurability in a mature, field-tested package - making it the preferred choice for industrial transmitters and process controllers where reliability, EMI resilience, and design continuity outweigh raw bit count.

Availability

AD7708BRU is available at Aetrix Electronics and suitable for industrial process control, pressure sensing, and portable instrumentation requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for AD7708BRU 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.

The AD7708BRU belongs to Analog Devices' precision Σ-Δ ADC product line, designed specifically for low-frequency, high-accuracy measurement front-ends in harsh industrial environments where noise immunity, reference flexibility, and long-term stability are critical.

FAQ

What is the maximum update rate of the AD7708BRU in non-chop mode?

The AD7708BRU achieves a maximum update rate of 1.365 kHz in non-chop (CHOP = 1) mode. This mode prioritizes channel throughput over ultra-low drift, making it suitable for applications like multiplexed data acquisition where speed is critical and moderate offset drift is acceptable. The actual achievable rate depends on selected gain, filter configuration, and reference voltage.

Does the AD7708BRU require an external crystal oscillator?

No, the AD7708BRU includes an on-chip crystal oscillator buffer and PLL that accept a standard 32.768 kHz crystal connected to XTAL1/XTAL2. This eliminates the need for external clock generation circuitry, reducing BOM count and board space - a key advantage for compact sensor modules and portable instruments where the AD7708BRU is commonly deployed.

Can the AD7708BRU measure both ratiometric and absolute signals on the same hardware?

Yes, the AD7708BRU supports both measurement types via its VREF Select™ feature. By configuring REFIN1 and REFIN2 appropriately - e.g., tying REFIN1(+) to sensor excitation and REFIN2(+) to a precision voltage reference - the AD7708BRU can switch between ratiometric (rejecting excitation drift) and absolute (traceable to metrology standards) modes without hardware changes, enhancing flexibility in smart transmitter designs.

What is the purpose of the P1 and P2 pins on the AD7708BRU?

The P1 and P2 pins on the AD7708BRU form a 2-bit general-purpose digital I/O port. They can be configured as inputs or outputs under software control via the I/O Control Register, enabling functions such as status indication (e.g., fault flag output), external device enable/disable control, or synchronization signaling with other system components - adding system-level functionality without requiring additional GPIO ICs.

How does the AD7708BRU handle 50 Hz and 60 Hz interference rejection?

The AD7708BRU provides hardware-based simultaneous 50 Hz and 60 Hz normal-mode rejection of ≥100 dB through its digital filter architecture and programmable settling times. This is achieved without firmware intervention - the rejection is inherent to the modulator and filter design, ensuring consistent mains-frequency noise suppression across all gain and update rate settings used by the AD7708BRU.