Analog Devices Inc. AD7859LASZ

Overview

AD7859LASZ from Analog Devices is a 12-bit, 8-channel, pseudo-differential sampling ADC optimized for low-power operation at up to 100 kSPS, featuring on-chip self- and system calibration, flexible 16-/8-bit parallel interface, and operation from a single 3 V to 5.5 V supply - used in battery-powered medical instruments and portable data acquisition systems.

For engineers reviewing the AD7859LASZ datasheet, AD7859LASZ pinout, AD7859LASZ application, or AD7859LASZ equivalent, key selection criteria include unipolar/bipolar input range support (0 to VREF or ±VREF/2), 500 ns track-and-hold acquisition time, 5.5 mW typical power dissipation at 3 V, and PQFP-44 package compatibility with legacy industrial control designs.

Technical Context

The AD7859LASZ employs a charge redistribution SAR architecture with integrated track-and-hold, internal 2.5 V reference buffer, and programmable analog input configuration (single-ended or pseudo-differential). Its calibration memory stores offset and gain correction coefficients applied during conversion.

Control logic supports software-initiated conversions via the CONVST bit in the write-only control register, hardware-triggered conversion via the CONVST pin, and multiple power-down modes managed by PMGT1/PMGT0 bits and the SLEEP input - enabling dynamic power scaling from 5.5 mW (normal) to 3.6 µW (full power-down).

Key Specifications

Pinout & Package

AD7859LASZ is housed in a 44-pin plastic quad flatpack (PQFP) package with 0.8 mm lead pitch and exposed thermal pad (not electrically connected). Pin 1 is marked by a corner chamfer; all NC pins must remain unconnected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7859ASZ, AD7859LASZ trades speed for 63% lower power at 3 V - critical for battery longevity; versus ADS7822U, it offers parallel throughput, integrated reference, and calibration at the cost of larger footprint and higher pin count.

Availability

AD7859LASZ is available at Aetrix Electronics and suitable for portable medical instrumentation, battery-powered data loggers, industrial control I/O modules, and pen-based computing interfaces requiring stable component supply across extended product lifecycles.

Supply support for AD7859LASZ 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 family was designed specifically for low-power, multi-channel data acquisition in portable and embedded systems - emphasizing calibration integrity, supply flexibility, and robust analog front-end performance.

FAQ

What is the maximum sampling rate supported by the AD7859LASZ?

The AD7859LASZ supports a maximum sampling rate of 100 kSPS, achieved with a 1.8 MHz master clock (CLKIN) and 18 clock cycles per conversion. This rate is fixed for the 'L' variant and cannot be increased beyond specification - attempting higher CLKIN frequencies violates timing margins and risks conversion errors. The AD7859LASZ datasheet confirms this limit applies across its full operating temperature range (–40°C to +85°C).

Does the AD7859LASZ require external reference components?

Yes, the AD7859LASZ requires two external capacitors: a 0.1 µF multilayer ceramic capacitor (CREF1) and a 0.01 µF ceramic disc capacitor (CREF2), both connected between their respective pins (CREF1, CREF2) and AGND. These stabilize the internal reference buffer and DAC switching transients. The AD7859LASZ does not operate reliably without them - missing or undersized capacitors cause reference droop and increased INL error.

Can the AD7859LASZ perform system calibration with an external reference?

Yes, the AD7859LASZ supports system calibration using an external reference applied to the REFIN/REFOUT pin. When CAL is asserted, the device measures system-level offset and gain errors relative to the external reference voltage and stores correction coefficients in on-chip calibration memory. This process requires the external reference to be stable within ±0.05 × VREF for offset and ±0.025 × VREF for gain, as specified in the AD7859LASZ calibration section.

What is the function of the W/B pin on the AD7859LASZ?

The W/B (Word/Byte) pin on the AD7859LASZ selects data bus width: when high, it enables 16-bit parallel transfer on DB0–DB15; when low, it enables 8-bit byte-mode transfer on DB0–DB7, with DB8 repurposed as HBEN (High Byte Enable). In byte mode, the low byte must be written before the high byte. This pin directly controls physical pin functionality - no internal register setting overrides its state.

How does power-down mode affect the BUSY signal behavior on the AD7859LASZ?

In full power-down mode (SLEEP = low, PMGT1 = 1, PMGT0 = 0), the BUSY signal remains low and inactive - it does not assert during wake-up or conversion initiation. The AD7859LASZ requires ~1 µs to exit power-down before BUSY becomes functional; therefore, software must insert a delay after clearing SLEEP before polling BUSY. This behavior is explicitly documented in the AD7859LASZ timing specifications table under "Sleep Mode" conditions.