Analog Devices Inc. AD7708BR

Overview

AD7708BR from Analog Devices is a 16-bit sigma-delta analog-to-digital converter (ADC) with integrated programmable gain amplifier (PGA), 8-channel pseudo-differential or 4-channel fully differential input capability, on-chip 32.768 kHz crystal oscillator, and SPI-compatible 3-wire serial interface. It operates from single 3 V or 5 V supplies and delivers up to 1.365 kHz output data rate with 16-bit no-missing-codes resolution - ideal for low-frequency industrial sensor signal acquisition in smart transmitters.

For engineers reviewing the AD7708BR datasheet, AD7708BR pinout, AD7708BR application, or AD7708BR equivalent, key selection considerations include its CHOP mode for enhanced noise rejection, VREF Select™ for ratiometric/absolute measurement flexibility, simultaneous 50 Hz/60 Hz line rejection, rail-to-rail input buffer, and factory-calibrated performance across –40°C to +85°C.

Technical Context

The AD7708BR implements a sigma-delta modulator with digital filter, programmable gain (1–128), and configurable chop mode (CHOP = 0 or 1) that trades off peak-to-peak resolution (up to 16 bits p-p at ±2.56 V range) against update rate (5.4 Hz to 1.365 kHz). Its internal PLL generates required clocking from an external 32.768 kHz crystal.

It integrates dual reference inputs (REFIN1±, REFIN2±), a 2-bit digital I/O port, and supports unipolar/bipolar coding. Analog inputs tolerate ±100 mV beyond AGND/AVDD rails when NEGBUF = 1, and feature 100 dB normal-mode rejection at 50/60 Hz with SF word configuration.

Key Specifications

Pinout & Package

AD7708BR is housed in a 28-lead SOIC package (R-28), with exposed pad not electrically connected. Pin functions are defined per Analog Devices' official pin configuration diagram and functional descriptions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7718BR, AD7708BR offers higher throughput (1.365 kHz vs. 105 Hz) at 16-bit resolution, while ADS124S08IPWR provides greater channel count and lower power but lacks on-chip oscillator and CHOP-based drift suppression - making AD7708BR optimal for balanced industrial DAQ where speed, precision, and noise immunity must coexist.

Availability

AD7708BR is available at Aetrix Electronics and suitable for industrial process control, smart transmitter design, and portable instrumentation requiring stable component supply, long-term manufacturability, and guaranteed lifecycle support.

Supply support for AD7708BR 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 Norwood, MA.

The AD7708BR belongs to Analog Devices' precision sigma-delta ADC product line, designed specifically for low-frequency, high-accuracy measurement applications including sensor conditioning, industrial automation, and portable test equipment.

FAQ

What is the maximum output data rate of the AD7708BR?

The AD7708BR achieves a maximum output data rate of 1.365 kHz in non-chop (CHOP = 1) mode. In chop mode (CHOP = 0), the maximum rate is 105 Hz. These rates are software-programmable via the Mode Register and depend on selected gain, filter configuration, and update rate word. The AD7708BR datasheet specifies these values under B-grade conditions at –40°C to +85°C.

Does the AD7708BR require an external crystal oscillator?

No - the AD7708BR includes an on-chip oscillator circuit compatible with a standard 32.768 kHz tuning-fork crystal connected to XTAL1/XTAL2 pins. This eliminates the need for external clock generation circuitry and reduces board space and BOM cost. The AD7708BR also supports external CMOS clock input if preferred.

Can the AD7708BR interface directly with a 3.3 V microcontroller SPI bus?

Yes - the AD7708BR supports 3 V operation with logic thresholds specified for DVDD = 3 V: VINL ≤ 0.4 V and VINH ≥ 2.0 V. Its SCLK input features a Schmitt trigger for noise immunity, and DOUT is fully compliant with 3.3 V logic levels (VOH ≥ DVDD – 0.6 V, VOL ≤ 0.4 V). No level-shifting is required when interfacing with 3.3 V MCUs.

How does the VREF Select™ feature work on the AD7708BR?

VREF Select™ allows the AD7708BR to operate in either ratiometric mode (using the same voltage that powers a sensor bridge as the reference) or absolute mode (using a dedicated precision reference). This is implemented via dual reference input pairs (REFIN1±, REFIN2±), enabling flexible system-level calibration strategies without hardware modification. The AD7708BR automatically detects and adapts to the configured reference topology.

Is the AD7708BR pin-compatible with any higher-resolution alternatives?

Yes - the AD7708BR is pin-for-pin compatible with the AD7718BR, a 24-bit variant in the same family. Both share identical pinout, register map, and communication protocol. This allows direct hardware replacement and firmware reuse, providing an upgrade path to higher resolution without PCB redesign - a key advantage confirmed in the AD7708/AD7718 datasheet ordering guide.