Analog Devices Inc. AD7858LARS

Overview

AD7858LARS from Analog Devices is a 12-bit, 100 kSPS successive approximation register (SAR) analog-to-digital converter optimized for low-power operation in battery-powered systems. It features eight single-ended or four pseudo-differential analog inputs, on-chip 2.5 V reference, system/self-calibration, and SPI/QSPI/8051-compatible serial interface. Designed for medical instruments and portable instrumentation, it operates from a single 3 V to 5.5 V supply with 4.5 mW typical power dissipation at 3 V.

For engineers reviewing the AD7858LARS datasheet, AD7858LARS pinout, AD7858LARS application, or AD7858LARS equivalent, key selection considerations include its 100 kSPS throughput, 12-bit resolution with ±1 LSB integral nonlinearity, 24-pin SSOP package, and support for automatic power-down after conversion - critical for energy-constrained embedded data acquisition.

Technical Context

The AD7858LARS implements a charge redistribution DAC-based SAR architecture with integrated track-and-hold, supporting both system and self-calibration modes. Its input stage accepts 0 V to VREF (up to AVDD) signals and provides channel-to-channel isolation of –90 dB at 25 kHz.

It uses a flexible 16-bit serial interface with frame-sync (SYNC), serial clock (SCLK), and bidirectional DIN/DOUT lines, configurable for SPI, QSPI, or 8051 protocols. Calibration is initiated via the CAL pin or software control register, with full self-calibration time of 31.25 ms at 1 MHz CLKIN.

Key Specifications

Pinout & Package

AD7858LARS is housed in a 24-lead small shrink outline package (SSOP), 0.154" wide, with standard JEDEC MS-013AC footprint and 0.025" lead pitch. Thermal impedance is 115°C/W (θJA), suitable for compact PCB layouts with moderate airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADS7822U and MAX11131ETE+, the AD7858LARS uniquely balances 12-bit accuracy, built-in calibration, pseudo-differential input flexibility, and ultra-low 4.5 mW active power - making it optimal for portable instrumentation where measurement integrity and battery longevity are co-prioritized.

Availability

AD7858LARS is available at Aetrix Electronics and suitable for battery-powered medical instruments, portable data loggers, and industrial handheld testers requiring stable component supply and long-term lifecycle support.

Supply support for AD7858LARS 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 Norwood, MA.

The AD7858LARS belongs to Analog Devices' precision SAR ADC product line, engineered specifically for low-power, high-accuracy data acquisition in portable and battery-operated instrumentation.

FAQ

What is the maximum sampling rate supported by the AD7858LARS?

The AD7858LARS supports a maximum sampling rate of 100 kSPS, verified under specified conditions: VDD = 3.0 V to 5.5 V, fCLKIN = 1 MHz (–40°C to +85°C) or 1.8 MHz (0°C to +70°C), and REFIN/REFOUT = 2.5 V. This throughput is fixed for the "L" variant and is lower than the 200 kSPS of the standard AD7858, reflecting its low-power optimization. The AD7858LARS achieves this rate with 4.6 µs conversion time at 1 MHz CLKIN.

Does the AD7858LARS require external reference components?

Yes, the AD7858LARS requires two external capacitors on its reference pins: a 0.1 µF multilayer ceramic capacitor (CREF1) and a 0.01 µF ceramic disc capacitor (CREF2), both connected between their respective pins and AGND. These stabilize the internal 2.5 V reference and support DAC charge redistribution. No external voltage reference IC is needed unless overriding the internal 2.5 V with a higher-precision source via the REFIN/REFOUT pin.

How is calibration performed on the AD7858LARS?

Calibration on the AD7858LARS can be initiated either automatically on power-up (by connecting a 10 nF capacitor from CAL to DGND) or manually via rising edge on the CAL pin. It supports system calibration (correcting external gain/offset errors) and self-calibration (correcting internal DAC and comparator errors). Full self-calibration takes 31.25 ms at 1 MHz CLKIN and stores results in on-chip calibration registers, retaining values through sleep mode.

What package type is used for the AD7858LARS?

The AD7858LARS is supplied in a 24-lead small shrink outline package (SSOP), designated RS-24 in Analog Devices' ordering guide. It measures 0.154" wide with 0.025" lead pitch and complies with JEDEC MS-013AC mechanical specifications. This package offers improved thermal performance over DIP and smaller footprint than SOIC, ideal for space-constrained portable designs.

Can the AD7858LARS interface directly with an 8051 microcontroller?

Yes, the AD7858LARS supports native 8051-compatible serial interface mode via its DIN, DOUT, SCLK, and SYNC pins. In this mode, it uses standard 8051 timing conventions and requires no additional level-shifting or protocol translation. The control register's 2/3 MODE bit configures the interface, and the part responds to 16-bit read/write commands aligned with 8051 firmware expectations - confirmed in Analog Devices' AD7858/AD7858L datasheet Rev. B, Table IX.