Analog Devices Inc. AD676KD

Overview

AD676KD from Analog Devices is a 16-bit successive-approximation analog-to-digital converter (SAR ADC) with on-chip sample-hold, autocalibration, and parallel digital output. It delivers 100 kSPS conversion rate, ±1.5 LSB integral nonlinearity, 87 dB S/(N+D), and operates from +5 V, +12 V, and –12 V supplies. It targets precision data acquisition in industrial instrumentation and automated test equipment.

For engineers reviewing the AD676KD datasheet, AD676KD pinout, AD676KD application, or AD676KD equivalent, key selection considerations include its 28-pin ceramic DIP package, bipolar input range up to ±10 V, 1 MHz full-power bandwidth, autocalibration timing (85,530 clock cycles), and twos-complement output coding for direct DSP interfacing.

Technical Context

The AD676KD implements a switched-capacitor charge-redistribution SAR architecture segmented across two monolithic chips-an analog BiMOS II ADC die and a digital DSP CMOS controller die-housed in one ceramic DIP package. Its autocalibration uses an on-chip microcontroller and calibration DAC to measure and correct capacitor mismatch errors for all top nine bits, storing correction values in RAM.

Conversion control relies on asynchronous SAMPLE and synchronous CLK signals: SAMPLE initiates acquisition (with 2 µs settling time), and 17 CLK edges execute the 16-bit approximation. BUSY asserts high during conversion or calibration, and output data (BIT 1–BIT 16) becomes valid on the falling edge of BUSY after the 17th CLK cycle.

Key Specifications

Pinout & Package

The AD676KD is housed in a 28-pin side-brazed ceramic DIP (package option D-28), with separate analog/digital grounds, dedicated AGND sense, and isolated power pins for optimal noise immunity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 16-bit SAR ADC applications.

Compared with AD7606BSTZ and ADS8860IDRCT, the AD676KD uniquely combines single-channel 87 dB S/(N+D), on-chip autocalibration, and parallel output in a through-hole ceramic package-making it optimal for legacy industrial controllers and repair-replacement scenarios where layout compatibility and minimal firmware integration are critical.

Availability

AD676KD is available at Aetrix Electronics and suitable for industrial process monitoring, automated test equipment, medical diagnostic instrumentation, and high-accuracy data loggers requiring stable component supply and long-lifecycle support.

Supply support for AD676KD 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.

The AD676 family was designed specifically for precision DC- and AC-coupled data acquisition systems demanding guaranteed 16-bit linearity without user calibration-targeting industrial, medical, and test equipment markets.

FAQ

What is the maximum recommended conversion time for AD676KD to maintain specified performance?

The AD676KD specifies a maximum conversion time (tC) of 1000 µs-from SAMPLE going HIGH to completion of the 17th CLK pulse. Exceeding this interval risks degraded INL and S/(N+D) due to capacitor charge leakage in the internal sample-hold and calibration storage elements. This limit applies per conversion, not between conversions.

Does AD676KD require external components for basic operation?

Yes, the AD676KD requires external bypass capacitors (0.1 µF ceramic per supply pin), a stable external voltage reference (5–10 V at VREF), and proper PCB layout with separated analog/digital ground planes. It does not require external sample-hold amplifiers or calibration circuitry due to its integrated autocalibration and on-chip SHA function.

How does the AGND SENSE pin improve measurement accuracy in AD676KD?

The AGND SENSE pin provides a Kelvin sense connection to the analog ground plane, allowing the AD676KD to reject voltage drops caused by return current flowing through PCB trace resistance. This ensures the internal analog circuitry references the true local ground potential at the ADC, reducing zero-error drift and improving common-mode rejection-especially critical in high-current industrial environments.

Can AD676KD operate with a 5 V-only supply configuration?

No. The AD676KD requires three independent supplies: +5 V (VDD), +12 V (VCC), and –12 V (VEE). The analog core-including the SAR array, sample-hold amplifier, and reference buffer-depends on the ±12 V rails for full-scale input range and distortion performance. Operating outside these specifications voids all ac and dc parameter guarantees.

What happens if the CAL pin is asserted during an active conversion of AD676KD?

Asserting CAL (driving it HIGH) during an active conversion performs an asynchronous hardware reset: BUSY immediately goes HIGH, the current conversion is aborted, and internal state registers are cleared. Calibration begins only upon the subsequent falling edge of CAL. This behavior allows safe reinitialization but discards any partially completed conversion result.