Analog Devices Inc. AD7818AR

Overview

AD7818AR from Analog Devices is a single-channel, 10-bit successive-approximation ADC with integrated temperature sensor, 9 μs conversion time for VIN1, and on-chip 2.5 V reference (±1% initial accuracy, 30 ppm/°C tempco). It operates from 2.7 V to 5.5 V and delivers ±2°C temperature measurement accuracy across −55°C to +125°C - used in battery-powered environmental monitoring systems where low-power, self-contained analog sensing is required.

For engineers reviewing the AD7818AR datasheet, AD7818AR pinout, AD7818AR application, or AD7818AR equivalent, key selection criteria include its single-ended analog input architecture, shared DIN/OUT serial interface, overtemperature indicator (OTI) output, automatic power-down at 4 μW (10 SPS), and compatibility with SPI/QSPI/MICROWIRE protocols without external clocking.

Technical Context

The AD7818AR implements a capacitor-based SAR architecture with inherent track-and-hold functionality and an internal oscillator - eliminating need for external clock circuitry. Its temperature sensor is hardwired to Channel 0 and provides 0.25°C resolution via direct ADC readout.

Conversion is initiated by falling edge of CONVST; BUSY goes high during conversion and OTI asserts low when sensed temperature exceeds programmable threshold stored in on-chip overtemperature register. Serial communication uses 3-wire interface (SCLK, RD/WR, DIN/OUT) with data clocked in on rising SCLK edge and out on falling edge.

Key Specifications

Pinout & Package

AD7818AR is housed in an 8-lead SOIC package (width 3.9 mm, body height 1.75 mm, lead pitch 1.27 mm), RoHS-compliant and rated for industrial temperature range (−40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 10-bit temperature-sensing ADC applications.

Compared with MAX1270BCPP+ and ADS7822U, the AD7818AR uniquely combines 10-bit resolution, integrated temperature sensor, on-chip reference, and OTI output in an 8-pin SOIC - delivering lowest system-level component count and fastest time-to-thermal-safety-enablement.

Availability

AD7818AR is available at Aetrix Electronics and suitable for environmental monitoring nodes, battery management systems, and industrial PLC analog input modules requiring stable component supply with guaranteed long-term availability.

Supply support for AD7818AR 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.

The AD7817/AD7818 product line was designed for embedded data acquisition systems needing integrated temperature awareness and low-power operation - targeting battery-powered sensors, industrial controls, and automotive subsystems.

FAQ

What is the maximum operating temperature range for the AD7818AR?

The AD7818AR is specified to operate from −40°C to +85°C (industrial grade), with its on-chip temperature sensor functional across −55°C to +125°C. This extended sensor range allows reliable thermal monitoring even under transient overtemperature conditions beyond the IC's own operational limits. The AD7818AR maintains ±2°C accuracy across the full −55°C to +125°C range when using its internal 2.5 V reference.

Does the AD7818AR require an external reference voltage?

No, the AD7818AR does not require an external reference voltage - it integrates a 2.5 V ±1% on-chip reference with 30 ppm/°C temperature coefficient. The REFIN pin is absent in the AD7818AR (unlike the AD7817), confirming exclusive use of the internal reference. This eliminates external reference components, reduces layout sensitivity, and ensures consistent full-scale scaling for both VIN and temperature measurements.

How does the overtemperature indicator (OTI) function in the AD7818AR?

The OTI pin in the AD7818AR is an active-low, open-drain output that asserts when the digitized temperature reading from Channel 0 exceeds the 8-bit value stored in the internal overtemperature register (OTR). It resets automatically at the end of a serial read operation (rising edge of RD/WR). This hardware-level interrupt enables immediate thermal shutdown without MCU polling - critical for safety-critical applications like battery chargers or motor controllers.

Can the AD7818AR measure both temperature and external voltage simultaneously?

No, the AD7818AR cannot measure temperature and external voltage simultaneously - it is a single-channel ADC with time-multiplexed access: Channel 0 is reserved for the on-chip temperature sensor, and Channel 1 (VIN) is the sole external analog input. To acquire both values, sequential conversions are required - first read Channel 0 for temperature, then Channel 1 for voltage - with typical total latency under 36 μs (27 μs + 9 μs).

What serial interface protocols is the AD7818AR compatible with?

The AD7818AR supports SPI, QSPI, and MICROWIRE protocols via its 3-wire interface (SCLK, RD/WR, DIN/OUT). It uses mode 0 (CPOL = 0, CPHA = 0): data sampled on falling SCLK edge, latched on rising edge; RD/WR high for read, low for write. No external clock or frame synchronization is needed - the internal oscillator drives conversion timing independently of serial communication.