AD7720BRU-REEL

ADCs/DACs - Special Purpose Overview

The AD7720BRU-REEL is a 7th-order CMOS sigma-delta modulator from Analog Devices, housed in a 28-lead TSSOP package. It converts analog signals into a high-speed 1-bit data stream using a differential input range of 0 V to +2.5 V or ±1.25 V. The device operates on a single +5 V supply and features an integrated 2.5 V voltage reference. Key electrical parameters include a maximum master clock frequency of 12.5 MHz, a dynamic range of 90 dB, and a typical Signal-to-(Noise + Distortion) ratio of 90 dB in bipolar mode. It supports both unipolar and bipolar input configurations.

ADCs/DACs - Special Purpose Feature Summary

• 7th-order sigma-delta modulation architecture for high-resolution conversion
• Integrated 2.5 V bandgap voltage reference with buffer output
• Differential input capability supporting unipolar (0–2.5 V) and bipolar (±1.25 V) modes
• Master clock frequency up to 12.5 MHz with internal oscillator circuitry

ADCs/DACs - Special Purpose Applications

• High-resolution industrial process control systems
• Precision weighing scales and load cell interfaces
• Medical instrumentation requiring low-noise signal acquisition
• Data acquisition systems utilizing external digital decimation filters

ADCs/DACs - Special Purpose Procurement Notes

Verify the REEL suffix indicates tape-and-reel packaging upon procurement. Confirm that the B version meets the required -40 °C to +85 °C operating temperature range. Ensure the receiving system includes appropriate digital filtering, as the AD7720 outputs a raw bit stream rather than a parallel word.

ADCs/DACs - Special Purpose Selection Notes

Select this component when a high-speed 1-bit output is acceptable and external digital filtering is available. Compare against the AD7722 if an integrated digital filter is required to avoid additional board space. Ensure the driving source can handle the switched-capacitor input impedance, which varies with the master clock frequency.

ADCs/DACs - Special Purpose Part Context

The AD7720 is part of the AD772x family of sigma-delta modulators. Unlike the AD7722, it does not contain an on-chip digital filter, requiring the user to implement decimation logic externally. It serves as a cost-effective solution for applications where the digital processing resources are already present in the host microcontroller or DSP.

ADCs/DACs - Special Purpose Replacement Considerations

The AD7722BRUZ is a direct functional replacement if an integrated digital filter is needed, though it adds complexity. For pin-compatible alternatives without integrated filters, verify specifications against other 28-lead TSSOP sigma-delta modulators from Analog Devices.

ADCs/DACs - Special Purpose FAQ

How is the common-mode bias handled in bipolar mode?

In bipolar mode, the inputs are centered about a common-mode bias. The datasheet specifies a common-mode voltage of 2.5 V for optimal performance, achieved by biasing VIN(-) at 1.25 V.

What is the function of the MZERO and GC pins?

MZERO grounds the modulator inputs internally to measure offset errors, while GC enables gain error calibration. These pins facilitate on-chip calibration procedures.

Can the AD7720 operate with an external reference?

Yes. An external reference can be applied to REF1 to overdrive the internal reference, or to REF2 with REF1 grounded to disable the internal buffer and minimize gain errors.