AD7781BRZ

Overview

The AD7781BRZ is a 20-bit Sigma-Delta ADC in a 16-lead TSSOP package. It features a pin-programmable PGA with gains of 1 or 128, and two selectable update rates: 10 Hz (FILTER=1) and 16.7 Hz (FILTER=0). Operating on a single supply from 2.7 V to 5.25 V, it consumes 330 μA at gain 128. The device includes an internal oscillator, simultaneous 50/60 Hz rejection, and a bridge power-down switch. It utilizes a read-only SPI-compatible serial interface for data output.

Feature Summary

• Pin-programmable filter response and in-amp gain selection
• Integrated low-noise programmable gain amplifier
• Internal clock oscillator eliminates external crystal requirements
• On-chip bridge power-down switch for sensor current control

Applications

• Weigh scales
• Pressure measurement
• Industrial process control
• Portable instrumentation

Procurement Notes

Verify the specific grade (B or C) required for noise specifications, as RMS noise values differ between grades. Confirm the package type matches the design footprint, as the AD7781 is available in both SOIC and TSSOP variants. Ensure the ordering suffix corresponds to the desired packaging format.

Selection Notes

Select Gain = 128 for high-resolution applications requiring small differential input ranges, such as load cells. Choose Gain = 1 for larger signal inputs. Select the 10 Hz rate for superior stop-band attenuation against mechanical vibrations, or the 16.7 Hz rate for faster settling times. Ensure DVDD and AVDD supplies are within the 2.7 V to 5.25 V range.

Part Context

The AD7781 is part of Analog Devices' low-power Sigma-Delta ADC family designed for precision front-end applications. It integrates the modulator, PGA, and digital filter into a single chip, reducing external component count. This integration makes it suitable for battery-operated systems where power consumption and board space are critical constraints.

Replacement Considerations

The AD7782 is a related device offering multiple channels and higher resolution. Verify pin compatibility if substituting, as pinouts may differ. Check if the additional channels or different architecture meet the system's performance requirements without redesigning the PCB layout.