Analog Devices Inc. AD7921AUJ-R2

Overview

AD7921AUJ-R2 from Analog Devices is a 12-bit, dual-channel successive approximation ADC with 250 kSPS throughput, operating from a single 2.35 V to 5.25 V supply and delivering 71 dB minimum SNR at 100 kHz input frequency. It features internal VDD-referenced conversion, no pipeline delay, and SPI/QSPI/MICROWIRE/DSP-compatible serial interface - deployed in portable medical instruments and battery-powered data acquisition systems.

For engineers reviewing the AD7921AUJ-R2 datasheet, AD7921AUJ-R2 pinout, AD7921AUJ-R2 application, or AD7921AUJ-R2 equivalent, key selection criteria include guaranteed 12-bit no-missed-codes performance, channel-to-channel isolation of −90 dB, 290 ns track-and-hold acquisition time, standby current ≤1 μA, and TSOT-8 package compatibility with space-constrained embedded designs.

Technical Context

The AD7921AUJ-R2 implements a true successive approximation register (SAR) architecture with on-chip track-and-hold amplifier capable of >6 MHz input bandwidth. Conversion is initiated on the falling edge of CS, with sampling synchronized to that edge and no latency between command and sample capture.

It uses VDD as its internal reference source, enabling full-scale analog input range of 0 V to VDD. Channel selection is performed via DIN pin during CS assertion, and output data includes a channel identifier bit followed by 12 MSB-first bits - supporting deterministic, low-overhead microprocessor interfacing without external reference or timing calibration.

Key Specifications

Pinout & Package

AD7921AUJ-R2 is housed in an 8-lead TSOT package (2.1 mm × 1.6 mm × 0.8 mm), optimized for compact PCB layouts in portable instrumentation and wearables.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-channel SAR ADC applications.

Compared with AD7921AUJ-R2, AD7911AUJ-R2 offers identical form-factor and interface with reduced resolution and SNR, while ADS8325IDRCT trades speed and integration for higher resolution but demands external reference and board redesign.

Availability

AD7921AUJ-R2 is available at Aetrix Electronics and suitable for portable medical instrumentation, battery-powered data acquisition, optical sensor interfaces, and industrial control loop sampling requiring stable component supply and long-term production continuity.

Supply support for AD7921AUJ-R2 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 AD7921AUJ-R2 belongs to Analog Devices' precision SAR ADC product line, engineered for low-power, high-accuracy data acquisition in space- and energy-constrained embedded systems.

FAQ

What is the maximum sampling rate supported by the AD7921AUJ-R2?

The AD7921AUJ-R2 supports a maximum throughput rate of 250 kSPS under specified conditions (VDD = 2.35 V to 5.25 V, fSCLK = 5 MHz). This corresponds to a minimum conversion time of 3.2 μs and enables Nyquist-limited signal capture up to 125 kHz. The actual achievable rate depends on SCLK frequency and system-level timing margins, as defined in Table 3 of the AD7921AUJ-R2 datasheet.

Does the AD7921AUJ-R2 require an external voltage reference?

No, the AD7921AUJ-R2 uses its VDD supply as the internal reference source, establishing a full-scale input range of 0 V to VDD. This eliminates the need for external reference components, reduces BOM count, and improves supply rejection. Reference-related errors scale with VDD stability, so clean, well-regulated supply design remains critical for optimal performance.

How is channel selection implemented on the AD7921AUJ-R2?

Channel selection on the AD7921AUJ-R2 is controlled via the DIN pin during the CS assertion window. A logic high or low on DIN at the falling edge of CS selects VIN1 or VIN0, respectively. The selected channel's conversion result is then output on DOUT with a channel identifier bit embedded in the 16-bit serial frame, ensuring unambiguous identification without additional control lines.

What is the meaning of "no pipeline delay" in the context of the AD7921AUJ-R2?

"No pipeline delay" means the AD7921AUJ-R2 is a true successive approximation ADC with atomic sampling and conversion - the result output corresponds exactly to the analog input sampled at the falling edge of CS, with no intermediate storage or multi-cycle latency. Unlike pipelined or sigma-delta converters, there is zero cycle-to-cycle phase shift or group delay, making it suitable for time-critical control and trigger-based acquisition.

Can the AD7921AUJ-R2 operate from a 2.5 V supply?

Yes, the AD7921AUJ-R2 is fully specified for operation from 2.35 V to 5.25 V, including 2.5 V. At 2.5 V, it maintains 12-bit resolution, no missing codes, and 250 kSPS throughput, with typical power consumption of ~2 mW. Logic thresholds scale with VDD (e.g., VINH ≥ 0.7 × VDD), ensuring robust digital interface behavior across the entire supply range.