Analog Devices Inc. AD7856AN

Overview

AD7856AN from Analog Devices is a 14-bit, 285 kSPS successive-approximation ADC operating from a single 5 V supply, featuring eight single-ended or four pseudo-differential analog inputs, on-chip 4.096 V reference support, and self/system calibration. It targets high-accuracy data acquisition in portable instrumentation and battery-powered control systems.

For engineers reviewing the AD7856AN datasheet, AD7856AN pinout, AD7856AN application, or AD7856AN equivalent, key selection considerations include its 24-pin DIP package, SPI/QSPI/8051-compatible serial interface, ±2 LSB integral nonlinearity, 78 dB SNR at 10 kHz input, and automatic power-down mode delivering 2.5 mW typical standby power.

Technical Context

The AD7856AN integrates a charge-redistribution SAR core with a track-and-hold amplifier acquiring in 500 ns, a flexible serial interface supporting Mode 1 (two-wire) and Mode 2 (three-wire), and dual power management bits (PMGT1/PMGT0) enabling full or partial power-down. Its internal calibration memory retains offset/gain coefficients across sleep cycles.

It supports system-level calibration via external reference injection and uses straight binary coding with 0 V to VREF input range. The device accepts external references from 1.2 V to VDD and maintains channel-to-channel isolation of –90 dB at 25 kHz, critical for multi-channel simultaneous sampling integrity.

Key Specifications

Pinout & Package

AD7856AN is housed in a 24-lead, 0.3-inch-wide plastic dual in-line package (DIP), with through-hole mounting and industry-standard lead pitch (0.1 inch). Pin 1 is marked by a notch or dot; pin numbering follows standard counter-clockwise orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 14-bit, medium-speed SAR ADC applications.

Compared with AD7856AN, AD7856AR offers identical functionality in surface-mount form for modern production, while ADS8320U trades speed and channel count for higher resolution and smaller size-making it suitable only where absolute precision supersedes sampling rate and input configuration needs.

Availability

AD7856AN is available at Aetrix Electronics and suitable for battery-powered medical instruments, industrial data loggers, and handheld test equipment requiring stable component supply and long-term obsolescence management.

Supply support for AD7856AN 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 AD7856AN belongs to Analog Devices' precision SAR ADC product line, engineered for applications demanding high DC accuracy, low power, and robust calibration in harsh or portable environments.

FAQ

What is the maximum sampling rate supported by the AD7856AN?

The AD7856AN achieves a maximum throughput rate of 285 kSPS under A-grade conditions (6 MHz master clock, –40°C to +105°C). This rate is sustained using Mode 2 serial interface with read operations performed during conversion, requiring ≥330 ns acquisition time before the next CONVST edge. At lower clock frequencies or in K-grade operation, the rate drops to 102 kSPS.

Does the AD7856AN require an external reference voltage?

No - the AD7856AN includes an internal 4.096 V reference accessible at the REFIN/REFOUT pin and usable directly. However, it also supports external references from 1.2 V to VDD, enabling higher precision or custom scaling. When using the internal reference, external capacitors CREF1 (0.1 µF) and CREF2 (0.01 µF) must be connected to AGND per the datasheet layout guidelines.

How does the AD7856AN handle power management in portable applications?

The AD7856AN provides three power states: normal (60 mW typ), full power-down (2.5 mW typ), and partial power-down (400 µA typ), all controlled via the SLEEP pin and PMGT1/PMGT0 bits in the control register. Automatic power-down activates after each conversion unless disabled, making it ideal for intermittent sensing in battery-powered systems like portable medical devices.

Can the AD7856AN interface directly with an 8051 microcontroller?

Yes - the AD7856AN's serial interface is explicitly designed for 8051 compatibility in both Mode 1 (two-wire, DIN bidirectional) and Mode 2 (three-wire, DIN input-only). It uses standard SPI timing with SYNC framing and requires no level-shifting when DVDD = 5 V, matching typical 8051 I/O voltage levels. Control register bit 5 (2/3 MODE) selects the interface mode.

What calibration options are available on the AD7856AN?

The AD7856AN supports automatic power-on self-calibration (via 10 nF capacitor on CAL pin), manual self-calibration (internal DAC and reference), and system calibration (using external reference applied to AIN+ and AIN–). Calibration coefficients are stored in on-chip registers and retained during SLEEP mode, ensuring accuracy recovery without reinitialization after wake-up.