Analog Devices Inc. AD7781BRUZ

Overview

AD7781BRUZ 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 oscillator, and integrated bridge power-down switch. Its 115–330 μA current draw supports battery-operated instrumentation.

For engineers reviewing the AD7781BRUZ datasheet, AD7781BRUZ pinout, AD7781BRUZ application, or AD7781BRUZ equivalent, key selection criteria include differential input range (±5 V / ±39 mV), RMS noise (44 nV at 10 Hz, gain = 128), p-p resolution (17.6 bits), 14-lead SOIC package, and 2-wire SPI-compatible interface with status bits appended to each conversion.

Technical Context

The AD7781BRUZ implements a 20-bit sigma-delta modulator with on-chip programmable gain amplifier (PGA) and digital filter, all controlled via dedicated pins-no register programming required. Its two-pin-selectable filter modes deliver either fast settling (120 ms at 16.7 Hz) or high stop-band attenuation (>−45 dB at 10 Hz), enabling mechanical vibration rejection in load cells.

It operates with independent analog (AVDD: 2.7–5.25 V) and digital (DVDD: 2.7–5.25 V) supplies, supports ratiometric bridge sensing, and includes a 9 Ω bridge power-down switch (BPDSW) controlled by PDRST. The DOUT/RDY pin serves as both data-ready indicator and serial output, delivering a 32-bit word (20-bit result + 8 status bits) synchronized to SCLK.

Key Specifications

Pinout & Package

AD7781BRUZ is supplied in a 14-lead, narrow-body SOIC package (package code BRUZ). Pin functions are fully pin-programmable-no configuration registers-and all control is performed via dedicated logic inputs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7781BRUZ, AD7190BRUZ delivers superior resolution and bandwidth at prohibitive power cost, while ADS1232IPW offers similar resolution but requires added components to match AD7781BRUZ's integrated 50/60 Hz rejection and bridge power control-making AD7781BRUZ optimal for low-power, self-contained bridge sensor designs.

Availability

AD7781BRUZ is available at Aetrix Electronics and suitable for weigh scales, pressure transducers, and portable instrumentation requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for AD7781BRUZ 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, founded in 1965 and headquartered in Wilmington, MA.

The AD7781BRUZ belongs to Analog Devices' precision sigma-delta ADC product line, designed specifically for low-power, high-accuracy bridge sensor signal conditioning in industrial and portable measurement systems.

FAQ

What is the maximum allowed analog input voltage range for AD7781BRUZ?

The AD7781BRUZ supports a differential input voltage range of ±V_REF/gain. With V_REF = 5 V and gain = 1, the range is ±5 V; with gain = 128, it is ±39 mV. Absolute voltage limits are GND + 450 mV to AVDD − 1.1 V (gain = 128, FILTER = 0) or GND + 1.5 V to AVDD − 1.5 V (gain = 128, FILTER = 1, AVDD > 3.6 V). Exceeding these violates absolute maximum ratings and degrades linearity.

Does AD7781BRUZ require an external crystal or clock source?

No, AD7781BRUZ does not require an external crystal or clock source. It contains a fully integrated 64 kHz ±3% internal clock oscillator, eliminating external timing components and reducing board area and BOM cost. The oscillator powers up automatically upon exit from power-down mode, with ~1 ms stabilization time before valid conversions begin.

How does the AD7781BRUZ achieve simultaneous 50 Hz and 60 Hz rejection?

The AD7781BRUZ achieves simultaneous 50 Hz and 60 Hz rejection through its fixed digital filter architecture, which provides ≥72 dB attenuation at both frequencies across both update rates (10 Hz and 16.7 Hz). This is implemented in hardware-not software-so no host processor intervention or configuration is needed. The filter response is selected solely by the FILTER pin state.

Can AD7781BRUZ interface directly with a 3.3 V microcontroller?

Yes, AD7781BRUZ can interface directly with a 3.3 V microcontroller. Its DVDD supply is independent of AVDD and operates from 2.7 V to 5.25 V. When DVDD = 3.3 V, the DOUT/RDY output high level is ≥2.7 V (DVDD − 0.6 V), and input logic thresholds (VINH = 1.8 V, VINL = 0.4 V) are fully compatible with standard 3.3 V CMOS levels-no level-shifting circuitry is required.

What is the function of the BPDSW pin on AD7781BRUZ?

The BPDSW pin on AD7781BRUZ is the bridge power-down switch terminal. It connects in series with the low-side of the sensor bridge (e.g., load cell). When PDRST is high, the internal 9 Ω switch closes, enabling excitation current flow; when PDRST is low, the switch opens, cutting off bridge current to minimize system power consumption-critical for battery longevity in portable instrumentation.