Analog Devices Inc. AD7851ARZ

Overview

AD7851ARZ from Analog Devices is a 14-bit, 333 kSPS serial analog-to-digital converter (ADC) with pseudo-differential input, on-chip 4.096 V reference, self- and system-calibration capability, and flexible SPI/QSPI/8051-compatible serial interface. It operates from a single 5 V supply, delivers ±2 LSB integral nonlinearity (A grade), and supports unipolar (0 V to VREF) and bipolar (±VREF/2) input ranges for precision data acquisition in high-speed control loops.

For engineers reviewing the AD7851ARZ datasheet, AD7851ARZ pinout, AD7851ARZ application, or AD7851ARZ equivalent, this page provides verified technical context, real-world design meaning of key specs, validated SOIC-24 pin functions, calibrated performance boundaries at 125°C, and two field-tested alternative ADCs with documented functional trade-offs.

Technical Context

The AD7851ARZ implements a charge redistribution SAR architecture with integrated track-and-hold, internal 4.096 V reference, and programmable analog input range selection via AMODE pin. Its conversion cycle requires 19.5 CLKIN cycles (max 3.25 µs at 6 MHz), with acquisition time of 3.0 µs and full-power bandwidth of 20 MHz.

It features five serial interface modes-including self-clocking (SCLK output) and external-clock (SCLK input) variants-with POLARITY and SYNC pins enabling polarity and frame synchronization control. Calibration registers support read/write access to offset and gain correction values, with automatic power-up calibration ensuring accuracy over temperature.

Key Specifications

Pinout & Package

AD7851ARZ is packaged in a 24-lead SOIC (R-24) with 0.3-inch width, RoHS-compliant (Z suffix), and thermal impedance θJA = 75°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7851ARZ, AD7852BRZ trades internal reference and sleep power for 3.3 V compatibility and reduced cost, while ADS8325IPW offers 2 extra bits at half the throughput and no on-chip calibration - making AD7851ARZ optimal for 5 V, high-speed, self-calibrating applications requiring minimal external components.

Availability

AD7851ARZ is available at Aetrix Electronics and suitable for motor control feedback, spectrum analyzer front-ends, and automotive battery monitoring requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7851ARZ 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 AD7851 belongs to Analog Devices' precision high-speed ADC product line, designed for demanding industrial, automotive, and instrumentation applications where accuracy, speed, and calibration integrity must coexist under wide temperature and supply variation.

FAQ

What is the maximum operating temperature for AD7851ARZ?

The AD7851ARZ is rated for operation from –40°C to +125°C. At 125°C, its guaranteed throughput rate is 238 kSPS (with 5 MHz CLKIN), maintaining ±2 LSB integral nonlinearity and full functionality of self-calibration, sleep mode, and serial interface. This makes AD7851ARZ suitable for under-hood automotive and industrial motor drive environments where ambient heat exceeds 100°C.

Does AD7851ARZ require external reference components?

Yes, AD7851ARZ requires two external capacitors on CREF1 and CREF2 pins: a 0.1 µF ceramic disc in parallel with a 470 nF tantalum for CREF1, and a 0.01 µF ceramic disc for CREF2. These stabilize the internal DAC charge redistribution network and reference node. The part includes an internal 4.096 V reference, so no external reference IC is needed unless higher accuracy or different voltage is required.

How does the AMODE pin affect AD7851ARZ input configuration?

The AMODE pin selects between two analog input ranges: logic low configures unipolar mode (0 V to VREF), requiring AIN(–) ≥ AGND and AIN(+) ≥ AIN(–); logic high configures bipolar mode (±VREF/2), requiring AIN(–) biased to VREF/2 and AIN(+) constrained between 0 V and AVDD. This pin directly determines input biasing strategy and signal conditioning circuitry in the front-end design.

Can AD7851ARZ perform calibration while powered down?

No, AD7851ARZ cannot perform calibration in sleep mode. Calibration (self or system) requires normal power mode with SLEEP = logic high and active CLKIN. The CAL pin triggers calibration only when the device is awake and clocked; BUSY asserts high for the full duration (e.g., 41.7 ms typical for full self-calibration at 6 MHz). Sleep mode retains previously written calibration data but suspends all active circuitry including the reference and comparator.

What serial interface modes does AD7851ARZ support, and how are they selected?

AD7851ARZ supports five serial interface modes selected by SM1 and SM2 pin states and POLARITY pin level. Mode 1 is 2-wire 8051-compatible; Modes 2–3 are 3-wire SPI/QSPI with configurable clock polarity; Modes 4–5 are self-clocking (SCLK output) with internal clock division. Selection is hardware-configured at power-up - no register writes are needed to set the base interface mode, though control register bits configure advanced timing and polarity behavior.