Analog Devices Inc. AD7859ASZ

Overview

AD7859ASZ from Analog Devices is a 12-bit, 8-channel, 200 kSPS sampling analog-to-digital converter (ADC) operating from a single 3 V to 5.5 V supply. It features on-chip track-and-hold, self- and system calibration, flexible 16-/8-bit parallel interface, and pseudo-differential or single-ended input configuration - used in portable medical instruments and battery-powered instrumentation requiring high accuracy and low power.

For engineers reviewing the AD7859ASZ datasheet, AD7859ASZ pinout, AD7859ASZ application, or AD7859ASZ equivalent, key selection considerations include unipolar/bipolar input range support (0 to VREF or ±VREF/2), 4.5 µs conversion time at 4 MHz CLKIN, ±1 LSB integral nonlinearity (A-grade), 44-pin PQFP package, and power-down modes enabling 1.3 mW operation at 10 kSPS.

Technical Context

The AD7859ASZ employs a charge redistribution SAR architecture with integrated track-and-hold amplifier acquiring signals in 500 ns. Its internal 2.5 V reference (REFIN/REFOUT) supports external overdrive, and calibration memory enables both self-calibration (6 ms typical) and system-level offset/gain correction using external reference conditions.

Control logic implements a 14-bit write-only control register managing channel selection (CHSLT2–CHSLT0), analog mode (AMODE), power management (PMGT1/PMGT0), and calibration mode (CALMD/CALSLT1/CALSLT0). Interface flexibility includes W/B-selectable 16-bit word or 8-bit byte transfers via DB0–DB15 and HBEN-assisted byte addressing.

Key Specifications

Pinout & Package

AD7859ASZ is housed in a 44-pin plastic quad flatpack (PQFP) package with 0.8 mm lead pitch and exposed pad for thermal relief. Pin functions are electrically validated per Analog Devices Rev. A datasheet and confirmed for PQFP layout compatibility.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit, multi-channel, parallel-interface ADC applications.

Compared with AD7859BSZ, AD7859ASZ trades ±0.5 LSB INL for broader availability and lower unit cost; versus AD7859LASZ, it delivers double the throughput at 2.7× higher active power - making it optimal for speed-critical, battery-constrained systems needing >100 kSPS.

Availability

AD7859ASZ is available at Aetrix Electronics and suitable for portable medical instrumentation, battery-powered data loggers, industrial process control, and high-speed modem analog front-ends requiring stable component supply across production lifecycles.

Supply support for AD7859ASZ 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 AD7859 product line delivers high-speed, low-power, multi-channel SAR ADCs optimized for portable and embedded systems demanding precision, calibration flexibility, and single-supply operation - targeting instrumentation, medical, and communications markets.

FAQ

What is the maximum sampling rate supported by the AD7859ASZ?

The AD7859ASZ supports a maximum sampling rate of 200 kSPS, achieved with a 4 MHz master clock (CLKIN) and 4.5 µs conversion time. This rate is guaranteed across the full industrial temperature range (–40°C to +85°C) and applies specifically to the AD7859ASZ variant - distinct from the 100 kSPS AD7859LASZ. The AD7859ASZ maintains this throughput while delivering ±1 LSB integral nonlinearity and 70 dB SNR+D performance.

Does the AD7859ASZ require external reference components?

Yes, the AD7859ASZ requires two external capacitors connected to AGND: a 0.1 µF multilayer ceramic capacitor on CREF1 and a 0.01 µF ceramic disc capacitor on CREF2. These stabilize the internal 2.5 V reference (REFIN/REFOUT) and support charge redistribution during conversion. While the part provides a buffered 2.5 V output, omitting either capacitor degrades reference settling and increases INL error beyond ±1 LSB specification.

How does the AD7859ASZ handle analog input configuration for differential measurements?

The AD7859ASZ supports pseudo-differential input mode via the SGL/DIFF bit in its control register. When SGL/DIFF = 0, channels are paired (e.g., AIN1–AIN2, AIN3–AIN4) to form four differential inputs with common-mode rejection. The AMODE bit then selects unipolar (0 to VREF) or bipolar (±VREF/2) range. This configuration is validated in the AD7859ASZ datasheet and requires proper biasing of AIN(–) to +VREF/2 in bipolar mode - a requirement explicitly defined for AD7859ASZ operation.

Can the AD7859ASZ operate from a 3.3 V supply?

Yes, the AD7859ASZ operates from a single supply ranging from 3.0 V to 5.5 V, including standard 3.3 V rails. At 3.3 V, it delivers 15 mW typical power dissipation, 4.5 µs conversion time, and maintains full 12-bit performance with ±1 LSB INL. Logic thresholds scale accordingly: VINH = 2.1 V min and VINL = 0.6 V max for digital inputs, ensuring reliable interface with 3.3 V microcontrollers and FPGAs without level-shifting.

What calibration modes are available on the AD7859ASZ?

The AD7859ASZ supports two calibration modes selected via the CALMD bit: self-calibration (CALMD = 0) and system calibration (CALMD = 1). Self-calibration corrects internal offset and gain errors using on-chip references; system calibration adjusts for external circuit errors (e.g., sensor gain, PCB trace resistance) using user-applied reference voltages. Both modes are implemented in hardware and require no host firmware algorithms - a capability confirmed for AD7859ASZ in the Rev. A datasheet calibration section.