Analog Devices Inc. AD7721AN

Overview

AD7721AN from Analog Devices is a 16-bit sigma-delta analog-to-digital converter with 468.75 kHz output word rate, 229.2 kHz input bandwidth, and on-chip FIR filtering. It operates from +5 V supplies, accepts differential analog inputs (0 V to 2.5 V or ±1.25 V), and features internal offset/gain calibration for <±4.88 mV full-scale error. It serves in high-accuracy data acquisition systems such as industrial process monitoring and precision instrumentation.

For engineers reviewing the AD7721AN datasheet, AD7721AN pinout, AD7721AN application, or AD7721AN equivalent, key selection considerations include its dual-mode serial/parallel interface, 16-bit resolution with no missing codes, standby power of 100 µW, differential input impedance of 20.8 kΩ at 15 MHz, and compatibility with external 2.5 V reference sources like the AD780.

Technical Context

The AD7721AN uses a single-bit sigma-delta modulator followed by two cascaded finite impulse response (FIR) digital filters, enabling inherent antialiasing with only first-order external filtering. Its analog input is continuously sampled at twice the master clock frequency (up to 30 MHz), eliminating need for external sample-and-hold circuitry.

It supports two distinct operating modes: serial mode (16-bit, 468.75 kHz OWR, 15 MHz max CLK) and parallel mode (12-bit, 312.5 kHz OWR, 10 MHz max CLK). Mode selection is determined at power-up via CS/RD/WR logic states, and configuration registers control UNI/BIPOLAR range, STBY, CAL, and DVAL/SYNC functionality.

Key Specifications

Pinout & Package

AD7721AN is housed in a 28-pin plastic DIP (N-28) package with 0.6-inch width and through-hole mounting. Pin functions are electrically validated per Analog Devices AD7721 Rev. A datasheet, with dedicated analog/digital ground separation (AGND, DGND, DSUBST) and strict layout requirements for noise immunity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar sigma-delta ADC applications.

Compared with AD7721AN, AD7722AR offers tighter integration but sacrifices interface flexibility and external reference control, while ADS1258IPW delivers superior resolution and built-in signal conditioning at the cost of reduced throughput and absence of parallel bus support.

Availability

AD7721AN is available at Aetrix Electronics and suitable for industrial process monitoring, precision instrumentation, motor drive current sensing, and medical signal acquisition requiring stable component supply across extended temperature ranges.

Supply support for AD7721AN 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 AD7721AN belongs to Analog Devices' precision sigma-delta ADC product line, designed specifically for high-speed, high-accuracy data acquisition in industrial and instrumentation applications where resolution, linearity, and low-power operation are critical.

FAQ

What is the maximum master clock frequency supported by the AD7721AN in serial mode?

The AD7721AN supports a maximum master clock frequency of 15 MHz in serial mode, which yields a 468.75 kHz output word rate and 229.2 kHz input bandwidth. Operation at this frequency is specified for guaranteed performance per the Rev. A datasheet; the device is characterized down to 100 kHz but rated for full specifications only up to 15 MHz in serial mode. The AD7721AN must be powered up with CS, RD, and WR tied low to enter serial mode.

How does the AD7721AN handle calibration of offset and gain errors?

The AD7721AN performs on-chip offset and gain calibration by internally shorting VIN1 and VIN2 during a CAL cycle initiated via the CAL/DB1 pin (serial) or control register bit DB1 (parallel). It computes an average of eight output results to populate the offset register and derives a gain correction factor. In normal operation, the offset register is subtracted from the filter output and the result multiplied by the gain factor. This calibration ensures AD7721AN maintains <±4.88 mV full-scale error across temperature.

Can the AD7721AN operate with a 3.3 V digital supply?

No, the AD7721AN requires AVDD and DVDD supplies of +5 V ±5% (4.75 V to 5.25 V) as specified in the Absolute Maximum Ratings and DC specifications tables. Its logic inputs require VIH ≥ 2.0 V and VIL ≤ 0.8 V, and output VOH ≥ 4.0 V under load - all defined relative to DVDD. Using 3.3 V violates the minimum DVDD requirement and will cause functional failure or damage. The AD7721AN is not 3.3 V compatible.

What is the purpose of the DSUBST pin on the AD7721AN?

The DSUBST pin on the AD7721AN is the substrate connection for the digital circuitry and must be connected via its own short, low-inductance path to AGND (Pin 24). This separate grounding prevents digital switching noise from coupling into the analog section and degrading AC performance metrics such as SNR and THD. Failure to properly connect DSUBST compromises the AD7721AN's specified 74 dB SNR and introduces ground bounce artifacts in high-resolution measurements.

Does the AD7721AN support simultaneous sampling of multiple channels?

No, the AD7721AN is a single-channel sigma-delta ADC with one differential analog input pair (VIN1/VIN2). It does not include multiplexing, channel sequencing, or auxiliary inputs. For multi-channel systems, discrete AD7721AN units or alternative devices such as the AD7723 (dual-channel variant) must be used. The AD7721AN's architecture focuses on optimizing performance for one high-fidelity channel rather than sharing resources across multiple inputs.