Analog Devices Inc. AD7858LARSZ

Overview

AD7858LARSZ from Analog Devices is a 12-bit, 100 kSPS, low-power successive approximation register (SAR) analog-to-digital converter with eight single-ended or four pseudo-differential input channels, internal reference buffer, and SPI/QSPI/μP-compatible serial interface - designed for battery-powered instrumentation and portable medical devices operating from 3 V to 5.5 V.

For engineers reviewing the AD7858LARSZ datasheet, AD7858LARSZ pinout, AD7858LARSZ application, or AD7858LARSZ equivalent, this page delivers verified electrical specifications, calibrated DC accuracy (±1 LSB INL), timing-critical interface behavior (1.8 MHz CLKIN, 10 μs max conversion time), and real-world system calibration support - all specific to the AD7858LARSZ SSOP-24 variant.

Technical Context

The AD7858LARSZ integrates a track-and-hold amplifier with 500 ns acquisition time, a charge redistribution DAC, on-chip 2.5 V reference buffer (REFIN/REFOUT), and a flexible serial controller supporting Mode 2 (CPOL = 0, CPHA = 0) and Mode 3 (CPOL = 1, CPHA = 0) protocols. It uses a 1.8 MHz master clock (CLKIN) for operation across –40°C to +85°C.

Calibration architecture includes automatic power-up self-calibration, system offset calibration (±0.05 × VREF span), and full-scale gain calibration (±0.025 × VREF span), all retained in nonvolatile memory during sleep mode. Power management supports three states: normal (1.9 mA @ 3 V), partial power-down (400 µA), and full power-down (5 µA with external clock off).

Key Specifications

Pinout & Package

AD7858LARSZ is housed in a 24-lead SSOP (Shrink Small Outline Package), 0.154-inch body width, 0.025-inch lead pitch, RoHS-compliant, moisture sensitivity level 3.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7858LARSZ, AD7490BRUZ offers higher throughput but lacks integrated calibration and sleep control, increasing BOM cost and firmware complexity; ADS7953IRHBT provides more channels and GPIO flexibility but consumes more power and occupies 3× the PCB area - making AD7858LARSZ optimal for space- and energy-constrained portable instrumentation.

Availability

AD7858LARSZ is available at Aetrix Electronics and suitable for portable medical devices, battery-powered data loggers, and industrial sensor interfaces requiring stable component supply, long-term lifecycle support, and RoHS-compliant SSOP packaging.

Supply support for AD7858LARSZ 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 Norwood, MA, with design centers worldwide and ISO 9001-certified manufacturing.

The AD7858LARSZ belongs to Analog Devices' precision SAR ADC product line, engineered specifically for low-power, high-accuracy data acquisition in portable and embedded systems where calibration stability, small size, and supply flexibility are critical.

FAQ

What is the maximum sampling rate supported by the AD7858LARSZ?

The AD7858LARSZ supports a maximum throughput rate of 100 kSPS, achieved with a 1.8 MHz master clock (CLKIN) across its full operating temperature range of –40°C to +85°C. This rate is fixed for the AD7858L variant and is lower than the 200 kSPS capability of the standard AD7858 - confirming AD7858LARSZ's optimization for low-power, not high-speed, applications. Conversion time is guaranteed at 10 µs maximum under these conditions.

Does the AD7858LARSZ require external decoupling capacitors on its reference pins?

Yes, the AD7858LARSZ mandates 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 (7 and 8) and AGND. These capacitors stabilize the internal DAC's charge redistribution network and are essential to achieve the specified ±1 LSB integral nonlinearity - omitting them degrades linearity beyond datasheet limits.

Can the AD7858LARSZ operate with an external reference voltage other than 2.5 V?

Yes, the AD7858LARSZ accepts external reference voltages from 1.2 V to AVDD on the REFIN/REFOUT pin (Pin 4). When using an external reference, the analog input range becomes 0 V to VREF, and full-scale resolution scales accordingly - e.g., a 3.0 V reference yields 732 µV per LSB. The internal 2.5 V reference remains available only when REFIN/REFOUT is left unconnected or tied to AVDD with CREF1 also tied to AVDD.

How does the SLEEP pin function in the AD7858LARSZ?

The SLEEP pin (Pin 3) controls power state: a logic low places the AD7858LARSZ into full power-down mode, disabling the internal reference, track-and-hold, and analog core while retaining calibration data in memory; a logic high restores normal operation. In full power-down with external clock disabled, supply current drops to 5 µA maximum - critical for extending battery life in intermittent-sampling applications like wearable health monitors.

Is the AD7858LARSZ pin-compatible with other variants in the AD7858 family?

Yes, the AD7858LARSZ shares identical pinout and package (SSOP-24) with AD7858AR, AD7858BR, AD7858LAR, and AD7858LBR - all are drop-in replacements in layout. However, performance differs: AD7858LARSZ is rated for 100 kSPS and 6.85 mW at 3.6 V, whereas AD7858AR operates at 200 kSPS and 20 mW. Firmware must be validated for timing changes, especially CONVST-to-BUSY delay and calibration durations.