AD7781CRUZ-REEL

Overview

The AD7781CRUZ-REEL is a 20-bit, pin-programmable, low-power Sigma-Delta analog-to-digital converter (ADC) manufactured by Analog Devices Inc. It features an integrated programmable gain amplifier (PGA) with selectable gains of 1 or 128 and an internal clock oscillator. The device operates on a single power supply ranging from 2.7 V to 5.25 V for both analog (AVDD) and digital (DVDD) domains. It offers two update rates: 16.7 Hz with a 120 ms settling time, and 10 Hz with a 300 ms settling time. Typical current consumption is 115 μA at Gain = 1 and 330 μA at Gain = 128. The component is housed in a 16-lead TSSOP package.

Feature Summary

• Pin-programmable filter response allows selection between fast settling (16.7 Hz) and high rejection (10 Hz) modes.
• Integrated bridge power-down switch enables direct control of sensor excitation to minimize system power consumption.
• Dedicated hardware pins configure gain, reset, and power-down states without requiring complex serial initialization sequences.
• Simultaneous 50 Hz/60 Hz line frequency rejection is provided at both available update rates.

Applications

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

Procurement Notes

Verify the specific grade (B or C) required for noise performance specifications before ordering. Confirm that the 16-lead TSSOP package matches the target PCB footprint. Ensure the DVDD supply voltage aligns with the microcontroller logic levels, as it is independent of AVDD. Check for RoHS compliance status if environmental regulations apply to the final assembly.

Selection Notes

Select the AD7781 when a complete front-end solution for bridge sensors is needed without external amplifiers. Choose this part over higher-speed ADCs if low power consumption and high resolution are prioritized. Consider the B Grade variant if lower RMS noise is critical compared to the standard C Grade. Verify that the input signal range fits within the ±VREF/gain limits for the chosen gain setting.

Part Context

The AD7781 is designed specifically for low-frequency, high-resolution measurements using resistive bridge sensors. It integrates the modulator, digital filter, PGA, and oscillator into a single chip, reducing the bill of materials for weigh scale and pressure gauge designs. The CRUZ suffix indicates the 16-lead TSSOP package variant.

Replacement Considerations

AD7781BRUZ is a compatible alternative in the same family, differing primarily in package type (SOIC vs. TSSOP). Verify pinout compatibility and thermal characteristics when substituting packages. No other direct functional equivalents exist in the public documentation for this specific configuration.

FAQ

How is the gain of the AD7781 configured?

The gain is set via the dedicated GAIN pin. A low logic level selects a gain of 128, while a high logic level selects a gain of 1.

What is the function of the BPDSW pin?

The BPDSW pin controls an internal low-side power switch that connects or disconnects the bridge sensor excitation. It is controlled by the PDRST pin state to save power when conversions are not active.

Can AVDD and DVDD be different voltages?

Yes, the analog supply (AVDD) and digital interface supply (DVDD) are independent. Both must remain within the 2.7 V to 5.25 V range, allowing for level shifting without external components.