AD7721ANZ

Overview

The AD7721ANZ is a complete low-power, 16-bit sigma-delta analog-to-digital converter manufactured by Analog Devices Inc. It operates from a single +5 V supply and accepts differential inputs of 0 V to 2.5 V or ±1.25 V. The device features an internal analog modulator that continuously samples the input at twice the clock frequency, eliminating the need for external sample-and-hold circuits. It supports both high-speed serial and parallel interfaces, with maximum clock frequencies of 15 MHz and 10 MHz respectively. The part includes on-chip offset and gain calibration, two cascaded FIR digital filters, and a standby mode reducing power consumption to 100 μW.

Feature Summary

• Utilizes a single-bit DAC in the modulator to ensure excellent linearity and DC accuracy without missing codes.
• Incorporates two series-connected finite impulse response (FIR) digital filters to reduce external antialiasing requirements.
• Features on-chip calibration logic to minimize zero-scale and full-scale errors for improved endpoint accuracy.
• Provides flexible interfacing through selectable serial or parallel ports compatible with modern microcontrollers.

Applications

• High-speed data acquisition systems requiring direct microcontroller interface
• Industrial process control applications utilizing differential sensor inputs
• Audio and vibration analysis equipment leveraging linear phase characteristics
• Portable instrumentation benefiting from low power standby modes

Procurement Notes

Verify the specific revision level and package option when sourcing components. Confirm that the operating temperature range aligns with industrial specifications. Ensure proper ESD handling procedures are followed during assembly due to the sensitivity of the CMOS construction. Cross-reference pin configurations against the latest datasheet revisions to avoid integration errors.

Selection Notes

Select this component for applications demanding high sampling rates up to 468.75 kHz with 16-bit resolution. Consider the serial interface for simplified wiring or parallel mode for higher throughput requirements. Evaluate the external clock frequency constraints, as performance metrics scale proportionally with the master clock input. Verify that the input voltage ranges match the sensor output specifications before finalizing the design.

Part Context

The AD7721 belongs to the AD7721 series of sigma-delta ADCs from Analog Devices. It is distinct from lower-speed variants like the AD7712 or AD7713, which prioritize precision over bandwidth. The 'AN' suffix indicates a plastic DIP package with an industrial temperature range. This model serves as a bridge between high-resolution slow converters and high-speed flash architectures.

Replacement Considerations

Direct replacements include the AD7721AR for SOIC packaging or the AD7721SQ for extended temperature ranges. For system upgrades, consider the AD7722 or AD7723 if additional channels or different interface options are required. Ensure pin compatibility and software register mappings remain consistent when substituting within the same family.

FAQ

Does the AD7721 require an external sample-and-hold circuit?

No, the analog input is continuously sampled by the internal analog modulator at twice the clock frequency, eliminating the need for external sample-and-hold circuitry.

How is the input bandwidth related to the clock frequency?

The input bandwidth, sample rate, filter corner frequency, and output word rate are all proportional to the external clock frequency. For example, a 15 MHz clock yields a 229.2 kHz input bandwidth.

What is the purpose of the DVAL pin?

The DVAL pin indicates when an overrange input signal has resulted in invalid data. It goes low if small overloads clip the output or if large overloads cause modulator instability.