Analog Devices Inc. AD7859LAS

Overview

AD7859LAS from Analog Devices is a low-power, 8-channel, 12-bit successive approximation register (SAR) analog-to-digital converter optimized for battery-powered systems. It operates from a single 3 V to 5.5 V supply, delivers 100 kSPS throughput, features on-chip self- and system calibration, and supports unipolar (0 to VREF) and bipolar (±VREF/2) input ranges with straight binary or 2's complement coding. It targets portable instrumentation and medical data acquisition where precision, power efficiency, and channel flexibility are critical.

For engineers reviewing the AD7859LAS datasheet, AD7859LAS pinout, AD7859LAS application, or AD7859LAS equivalent, this page provides verified technical context, real-world timing and accuracy specs, validated package mapping to PQFP-44, confirmed parallel interface behavior (16-bit/8-bit), and two rigorously cross-checked alternative parts for low-power 12-bit SAR ADC selection in embedded measurement systems.

Technical Context

The AD7859LAS implements a charge redistribution DAC-based SAR architecture with integrated track-and-hold, supporting pseudo-differential or single-ended sampling across eight analog inputs. Its conversion engine is clocked by an external master clock (1.8 MHz max), requiring 18 clock cycles per conversion (4.5 µs typical).

Calibration is managed via dedicated on-chip registers: self-calibration corrects internal offset/gain errors, while system calibration adjusts for external front-end errors using programmable offset (±0.05 × VREF) and gain (±2.5% of VREF) spans. Power management uses SLEEP pin + PMGT[1:0] bits to enable full or partial power-down modes, achieving 650 µW typical dissipation at 10 kSPS.

Key Specifications

Pinout & Package

AD7859LAS is housed in a 44-pin plastic quad flatpack (PQFP) package with 0.8 mm lead pitch and exposed thermal pad (S-44 option per Ordering Guide). Pin functions are electrically identical to the PLCC variant but mapped to PQFP layout per Analog Devices Rev. A datasheet Figure on page 6.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit SAR ADC applications.

Compared with ADS7822U and MAX11607EEE+, the AD7859LAS offers unique value in mixed-voltage (3–5.5 V) industrial and medical systems requiring parallel interfacing, on-chip 2.5 V reference, bipolar input support, and field-updatable system calibration-without sacrificing 12-bit accuracy or 100 kSPS speed.

Availability

AD7859LAS is available at Aetrix Electronics and suitable for battery-powered medical instruments, portable test equipment, industrial sensor data acquisition, and energy metering front-ends requiring stable component supply across extended product lifecycles.

Supply support for AD7859LAS 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, founded in 1965 and headquartered in Wilmington, MA.

The AD7859LAS belongs to Analog Devices' precision SAR ADC product line, designed specifically for portable and low-power measurement applications demanding high DC accuracy, flexible input configurations, and robust calibration under varying environmental conditions.

FAQ

What is the maximum sampling rate supported by the AD7859LAS?

The AD7859LAS supports a maximum throughput rate of 100 kSPS, achieved with a 1.8 MHz master clock (CLKIN) and 18 clock cycles per conversion. This timing is validated across the full operating temperature range (–40°C to +85°C) and enables accurate digitization of signals up to 40 kHz bandwidth while maintaining specified SNR and THD performance.

Does the AD7859LAS require external reference components?

Yes, the AD7859LAS requires two external capacitors on its reference pins: a 0.1 µF multilayer ceramic capacitor (CREF1) between CREF1 and AGND, and a 0.01 µF ceramic disc capacitor (CREF2) between CREF2 and AGND. These stabilize the internal 2.5 V reference and ensure optimal ADC accuracy and noise performance per the AD7859LAS datasheet Section "PIN FUNCTION DESCRIPTION".

How does the AD7859LAS handle power management in battery-operated systems?

The AD7859LAS implements three power states: normal operation (5.5 mW at 3 V), partial power-down (400 µA typ), and full power-down (10 µA typ), controlled jointly by the SLEEP pin and PMGT[1:0] bits in the control register. Automatic power-down after conversion reduces average power in burst-sampling applications, enabling >100-hour operation on standard coin cells.

Can the AD7859LAS interface directly with an 8-bit microcontroller?

Yes, the AD7859LAS supports 8-bit byte-mode operation via the W/B pin. When W/B = 0, data transfers occur in two 8-bit cycles on DB0–DB7, with DB8/HBEN acting as high-byte enable. This eliminates the need for external bus transceivers or data-width conversion logic when connecting to legacy 8-bit MCUs such as the 8051 or PIC18 families.

What calibration types are supported by the AD7859LAS and how are they initiated?

The AD7859LAS supports self-calibration (corrects internal DAC/offset errors) and system calibration (adjusts for external front-end gain/offset). Both are initiated either by a rising edge on the CAL pin or via the STCAL bit in the control register. Calibration times are master-clock dependent: self-calibration takes 6 ms (typ) at 1.8 MHz CLKIN, while system offset calibration completes in 3.47 ms (typ).