Analog Devices Inc. AD7781CRZ

Overview

AD7781CRZ from Analog Devices is a 20-bit, low-power sigma-delta ADC optimized for bridge sensor front ends in weigh scales and pressure transducers. It features pin-programmable gain (1 or 128), dual update rates (10 Hz / 16.7 Hz), simultaneous 50 Hz/60 Hz rejection, internal clock oscillator, and integrated bridge power-down switch. Its 115–330 μA current draw supports battery-operated instrumentation.

For engineers reviewing the AD7781CRZ datasheet, AD7781CRZ pinout, AD7781CRZ application, or AD7781CRZ equivalent, key selection criteria include differential input range (±39 mV at GAIN=128), RMS noise (44 nV typical), settling time (120 ms / 300 ms), −40°C to +105°C operation, and SOIC-14/TSSOP-16 package compatibility.

Technical Context

The AD7781CRZ implements a fully integrated sigma-delta modulator with on-chip programmable gain amplifier (PGA) and digital filter - all controlled via dedicated pins (GAIN, FILTER, PDRST). Its architecture eliminates external clocking and simplifies interface using a 2-wire read-only serial protocol compatible with SPI timing.

It supports ratiometric operation with unbuffered differential reference inputs (REFIN±), accepts analog input common-mode voltages from 0.5 V to AVDD, and includes a 9 Ω bridge power-down switch (BPDSW) controlled by PDRST. The device delivers simultaneous 50 Hz/60 Hz rejection at both update rates without external filtering.

Key Specifications

Pinout & Package

AD7781CRZ is available in a 14-lead, narrow-body SOIC package (RoHS-compliant, JEDEC MS-012). Pin functions are fixed and non-multiplexed; all control and interface signals are dedicated.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision sigma-delta ADC applications.

Compared with AD7781CRZ, AD7190BRUZ offers higher resolution and flexibility at significantly higher power and complexity, while ADS1232IPW provides basic 20-bit conversion without integrated power-switching or dual-mode line rejection - making AD7781CRZ uniquely suited for low-power, sensor-integrated industrial measurement.

Availability

AD7781CRZ is available at Aetrix Electronics and suitable for weigh scales, pressure transducers, and portable instrumentation requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant packaging.

Supply support for AD7781CRZ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA, with design and manufacturing operations worldwide.

The AD7781CRZ belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for low-power, high-accuracy bridge sensor signal conditioning in industrial and instrumentation applications.

FAQ

What is the maximum allowable analog input voltage range for AD7781CRZ at GAIN=128?

The AD7781CRZ supports a differential input voltage range of ±V_REF/gain. With GAIN=128 and a nominal 5 V reference, the full-scale range is ±39 mV. Absolute input voltage limits are GND + 450 mV to AVDD − 1.1 V (for FILTER=0), ensuring safe operation without clipping or linearity degradation. This range is confirmed in Table 2 of the AD7781CRZ datasheet under "Analog Input Voltage Limits".

Does AD7781CRZ require an external crystal or clock source?

No, AD7781CRZ does not require an external crystal or clock source. It integrates a factory-trimmed 64 kHz internal oscillator (±3% tolerance) that drives the sigma-delta modulator and digital filter. This eliminates BOM cost and board space for external timing components and is explicitly documented in the "INTERNAL CLOCK" section of the AD7781CRZ datasheet.

How does the BPDSW function work in AD7781CRZ, and what is its on-resistance?

The BPDSW (Bridge Power-Down Switch) in AD7781CRZ is a low-side MOSFET switch controlled by the PDRST pin. When PDRST is high, BPDSW closes (R_ON ≤ 9 Ω); when low, it opens, disconnecting the load cell from ground. It supports 30 mA continuous current and is designed to minimize system power in battery-operated applications - verified in the "BRIDGE POWER-DOWN SWITCH" section of the AD7781CRZ datasheet.

Can AD7781CRZ reject both 50 Hz and 60 Hz interference simultaneously?

Yes, AD7781CRZ provides simultaneous 50 Hz and 60 Hz rejection at both 10 Hz and 16.7 Hz update rates - delivering 63–90 dB attenuation depending on grade and configuration. This is achieved through its fixed digital filter architecture and is explicitly specified in the "Normal Mode Rejection" table (Table 2) of the AD7781CRZ datasheet, eliminating need for external notch filters.

What package options are available for AD7781CRZ, and is the SOIC-14 version RoHS-compliant?

AD7781CRZ is offered in two RoHS-compliant packages: 14-lead narrow-body SOIC (designated by "RZ" suffix) and 16-lead TSSOP ("RUZ"). The "CRZ" variant specifically denotes the SOIC-14 package with commercial temperature range (−40°C to +105°C) and lead-free finish, as confirmed in the "Ordering Guide" on page 16 of the AD7781CRZ datasheet.