Analog Devices Inc. AD7785BRUZ

Overview

AD7785BRUZ from Analog Devices is a 20-bit Σ-Δ analog-to-digital converter with integrated instrumentation amplifier, on-chip band gap reference (4 ppm/°C drift), and three differential input channels. It delivers 40 nV rms noise at 4.17 Hz update rate with gain = 64, consumes 400 μA typical supply current, and operates from 2.7 V to 5.25 V over –40°C to +105°C - enabling high-precision thermocouple and RTD measurements in portable industrial sensors.

For engineers reviewing the AD7785BRUZ datasheet, AD7785BRUZ pinout, AD7785BRUZ application, or AD7785BRUZ equivalent, key selection considerations include its simultaneous 50/60 Hz rejection capability, programmable excitation current sources (10/210/1000 μA), independent AVDD/DVDD supplies, and SPI-compatible 3-wire serial interface with Schmitt-triggered SCLK.

Technical Context

The AD7785BRUZ integrates a low-noise, programmable-gain instrumentation amplifier directly preceding its 20-bit Σ-Δ modulator, supporting gains from 1 to 128 and enabling direct connection of microvolt-level sensor signals without external signal conditioning. Its digital filter provides selectable output rates from 4.17 Hz to 470 Hz and inherent 50 Hz/60 Hz notch rejection via programmable FS[3:0] register bits.

It features dual excitation current sources (IOUT1/IOUT2) with ±0.5% matching and 200 ppm/°C drift, an on-chip bias voltage generator (VBIAS = AVDD/2), burnout currents for open-circuit detection, and support for both internal (1.17 V, 4 ppm/°C) and external (0.1 V to AVDD) references - all managed through eight dedicated on-chip registers accessible via SPI.

Key Specifications

Pinout & Package

AD7785BRUZ is housed in a 16-lead TSSOP package (4.4 mm × 5.0 mm, 0.65 mm pitch) with exposed pad for thermal enhancement. Pin functions are validated per Analog Devices Rev. 0 datasheet Figure 5 and Table 4.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7785BRUZ, AD7124-4BRUZ offers higher resolution but lacks the same level of integrated analog front-end functionality for direct thermocouple/RTD interfacing, while LTC2440CGN#PBF achieves lower noise only at significantly reduced update rates and requires full external signal chain implementation.

Availability

AD7785BRUZ is available at Aetrix Electronics and suitable for thermocouple measurement systems, RTD-based process transmitters, and portable medical analyzers requiring stable component supply, long-lifecycle support, and guaranteed traceability.

Supply support for AD7785BRUZ 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, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD7785BRUZ belongs to Analog Devices' precision Σ-Δ ADC product line, designed specifically for low-power, high-accuracy sensor signal acquisition in industrial, medical, and environmental monitoring equipment.

FAQ

What is the maximum achievable effective resolution of the AD7785BRUZ at 4.17 Hz update rate?

The AD7785BRUZ achieves up to 20-bit effective resolution at 4.17 Hz with gain = 64 and internal reference, delivering 40 nV rms noise. This corresponds to ~19.5 bits peak-to-peak resolution - sufficient for stable 0.1°C thermocouple readings without code flicker. The AD7785BRUZ maintains this resolution across its full –40°C to +105°C operating range when calibrated.

Does the AD7785BRUZ support true differential reference inputs?

Yes, the AD7785BRUZ supports true differential reference inputs via REFIN(+) and REFIN(–) pins (shared with AIN3). It accepts external references from 0.1 V to AVDD, with nominal 2.5 V differential input. Common-mode voltage must stay within GND + 0.1 V to AVDD − 0.1 V, and the device maintains 100 dB common-mode rejection at DC and 50/60 Hz when using external references.

Can the AD7785BRUZ perform simultaneous 50 Hz and 60 Hz rejection?

Yes, the AD7785BRUZ achieves simultaneous 50 Hz and 60 Hz rejection through its programmable digital filter. With FS[3:0] = 1010, it delivers ≥65 dB rejection at both frequencies using the internal clock; with external 64 kHz clock and FS[3:0] = 1010, rejection improves to ≥80 dB at both 50 Hz and 60 Hz - critical for global industrial deployments.

How does the AD7785BRUZ handle burnout detection for RTD sensors?

The AD7785BRUZ integrates dedicated burnout current sources that inject a small current (typically 10 μA) into the RTD lead path. By measuring resulting voltage shifts during idle cycles, open-circuit faults are detected without interrupting normal measurement sequences. This function is configurable per channel and works in conjunction with the AD7785BRUZ's built-in bias voltage generator for robust sensor health monitoring.

Is the AD7785BRUZ pin-compatible with other members of the AD77xx family?

No, the AD7785BRUZ is not pin-compatible with earlier AD77xx series devices such as AD7730 or AD7714. Its 16-lead TSSOP pinout, register map, excitation source routing (IOUT1/IOUT2), and dual-supply architecture (AVDD/DVDD) are unique to the AD7785BRUZ. Migration requires PCB layout revision and firmware register reconfiguration.