AD7721AN

Overview

The AD7721AN is a complete low-power, 16-bit sigma-delta analog-to-digital converter manufactured by Analog Devices Inc. It operates from a +5 V supply and accepts differential input ranges of 0 V to 2.5 V (unipolar) or ±1.25 V (bipolar). The device features an internal analog modulator that continuously samples inputs at twice the clock frequency, eliminating the need for external sample-and-hold circuits. Processing occurs via two cascaded finite impulse response digital filters. In serial mode with a 15 MHz master clock, it achieves a 468.75 kHz output word rate, 229.2 kHz input bandwidth, 97.07 μs settling time, and 48.53 μs group delay. Parallel mode supports up to 10 MHz clocks with 12-bit resolution.

Feature Summary

• Utilizes a single-bit DAC in the modulator architecture to ensure excellent linearity and DC accuracy without missing codes.
• Incorporates on-chip calibration logic for offset and gain errors to minimize zero-scale and full-scale deviations.
• Features dual interface options including a high-speed serial port with internal clocking and a parallel data bus.
• Provides integrated low-pass FIR digital filtering that reduces external antialiasing requirements to first-order components.

Applications

• High-speed data acquisition systems requiring direct interfacing with microcontrollers and DSPs.
• Industrial process control applications utilizing differential signal inputs.
• Test and measurement equipment demanding precise voltage digitization.
• Audio processing systems leveraging linear phase characteristics.

Procurement Notes

Verify the specific suffix 'AN' corresponds to the industrial temperature range (-40 °C to +85 °C) and N-28 plastic DIP package option. Confirm the revision level matches current manufacturing standards as datasheets may undergo updates. Ensure compatibility with +5 V power supplies within the specified tolerance limits before integration into final designs.

Selection Notes

Select this component when a 16-bit resolution with high throughput is required alongside low power consumption. Consider the serial interface for simplified wiring with modern processors or the parallel mode for higher speed data access. Evaluate the internal filtering capabilities against external antialiasing filter complexity requirements. Verify that the input voltage range aligns with the application's unipolar or bipolar signal needs.

Part Context

The AD7721 belongs to the Analog Devices family of sigma-delta ADCs designed for precision measurement. It represents a CMOS implementation optimized for low power dissipation while maintaining high dynamic performance. The device integrates both the analog front-end and digital filtering, reducing system component count compared to traditional architectures requiring external sample-and-hold amplifiers.

Replacement Considerations

No public confirmed substitute part numbers are available in the provided documentation. Designers should evaluate other Analog Devices sigma-delta converters based on resolution, speed, and interface requirements if replacement is necessary.

FAQ

How does the AD7721 handle external sampling requirements?

The analog input is continuously sampled by an internal analog modulator at twice the clock frequency, which eliminates the need for external sample-and-hold circuitry.

What is the function of the DVAL pin?

The DVAL pin indicates when an overrange input signal has resulted in invalid data. It goes low during small overloads or modulator instability caused by large overloads exceeding full scale by 20%.

How is endpoint accuracy maintained in the AD7721?

Endpoint accuracy is ensured by an on-chip calibration procedure that minimizes zero-scale and full-scale errors through the adjustment of offset and gain registers.