Analog Devices Inc. AD7781BRZ

Overview

AD7781BRZ from Analog Devices is a 20-bit, pin-programmable, low-power sigma-delta ADC optimized for bridge sensor front ends in weigh scales and pressure transducers. It integrates a programmable gain amplifier (gain = 1 or 128), on-chip oscillator, and bridge power-down switch. With 115 μA typical current at gain = 1 and simultaneous 50 Hz/60 Hz rejection, it delivers high-resolution measurement in battery-powered industrial instrumentation.

For engineers reviewing the AD7781BRZ datasheet, AD7781BRZ pinout, AD7781BRZ application, or AD7781BRZ equivalent, key selection considerations include its dual update rates (10 Hz / 16.7 Hz), differential input range (±5 V or ±39 mV), 2-wire SPI-compatible interface, −40°C to +105°C operation, and SOIC-14 package compatibility with legacy load cell signal chains.

Technical Context

The AD7781BRZ implements a 20-bit sigma-delta modulator with on-chip digital filtering and a dedicated PGA stage. Its filter response is selected via the FILTER pin, enabling either fast settling (120 ms, 16.7 Hz) or high stop-band attenuation (>−45 dB, 10 Hz). The GAIN pin directly configures PGA gain without register writes, supporting ratiometric bridge measurements with external reference voltages from 0.5 V to AVDD.

It features a dual-supply architecture: AVDD (2.7–5.25 V) powers analog circuitry including the bridge power-down switch (RON ≤ 9 Ω), while DVDD (2.7–5.25 V) independently supplies digital logic and the SCLK/DOUT/RDY interface. All control is pin-driven-no serial configuration required-and each data read appends eight status bits for transfer integrity verification.

Key Specifications

Pinout & Package

AD7781BRZ is supplied in a 14-lead, narrow-body SOIC package (package code BRZ), with 1.27 mm lead pitch and JEDEC MS-012AC footprint. Pin 1 is marked with a dot; pins 3, 15, and 16 are NC (no connect).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7781BRZ, AD7190BRUZ offers higher resolution and flexibility at increased complexity and power, while ADS1232IPW provides simpler integration for fixed-rate applications but sacrifices pin-level configurability and supply decoupling.

Availability

AD7781BRZ is available at Aetrix Electronics and suitable for weigh scales, pressure transmitters, industrial process controllers, and portable instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7781BRZ 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, serving industrial, automotive, communications, and healthcare markets since 1965.

The AD7781BRZ belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for low-power, high-accuracy bridge sensor signal conditioning in demanding industrial and instrumentation applications.

FAQ

What is the maximum allowed reference voltage for AD7781BRZ?

The AD7781BRZ accepts an external differential reference voltage (REFIN(+) − REFIN(−)) from 0.5 V up to AVDD. For example, if AVDD = 5.25 V, the maximum reference voltage is 5.25 V. Absolute voltage limits on REFIN(+) and REFIN(−) are GND − 30 mV to AVDD + 30 mV. Exceeding these violates absolute maximum ratings and may damage the device.

Does AD7781BRZ require an external crystal or clock source?

No, AD7781BRZ does not require an external crystal or clock source. It includes an internal 64 kHz ±3% oscillator that drives the sigma-delta modulator and digital filter. This eliminates BOM cost, board space, and layout sensitivity associated with external timing components-critical for compact, low-power designs.

How does the bridge power-down switch (BPDSW) function in AD7781BRZ?

In AD7781BRZ, the BPDSW terminal connects internally to GND and is controlled by the PDRST pin. When PDRST is high, BPDSW closes (RON ≤ 9 Ω), allowing current to flow through the bridge sensor. When PDRST is low, BPDSW opens, disconnecting the bridge from GND and halting sensor excitation-reducing system power consumption in battery-operated devices.

Can AD7781BRZ operate with different analog and digital supply voltages?

Yes, AD7781BRZ supports independent analog and digital supplies: AVDD (2.7–5.25 V) powers the ADC core and BPDSW, while DVDD (2.7–5.25 V) powers the SCLK, DOUT/RDY, and control pins. This allows AVDD = 5 V and DVDD = 3.3 V (or vice versa), easing integration into mixed-voltage systems without level-shifting circuitry.

What is the meaning of the status bits appended to each AD7781BRZ data read?

Each AD7781BRZ data read returns a 32-bit word: 20-bit conversion result, four zero bits, then eight status bits. These status bits contain a fixed pattern sequence used to verify serial transfer integrity-ensuring the host MCU correctly received the full conversion without bit slips or timing errors, especially in electrically noisy environments.