Analog Devices Inc. AD7711AQ

Overview

AD7711AQ from Analog Devices is a 24-bit charge-balancing sigma-delta ADC with integrated programmable-gain amplifier (PGA), dual RTD excitation current sources (200 µA each), and internal 2.5 V reference. It supports differential and single-ended analog inputs, offers ±0.0015% integral nonlinearity, and operates from single or dual supplies (AVDD = 5–10 V, VSS = 0 or –5 V) with typical power dissipation of 25 mW. It is designed for high-accuracy RTD-based temperature measurement in industrial process control systems.

For engineers reviewing the AD7711AQ datasheet, AD7711AQ pinout, AD7711AQ application, or AD7711AQ equivalent, this page delivers verified technical context, real-world timing and noise performance, calibrated RTD interface capability, filter notch programming, and validated alternative options - all grounded in the official AD7711 Rev. G datasheet and ordering guide.

Technical Context

The AD7711AQ implements a charge-balancing sigma-delta modulator with on-chip digital filtering, where the first notch frequency is software-programmable via the 24-bit control register to set cutoff (e.g., 10 Hz, 50 Hz, 60 Hz) and settling time. Its analog front end includes a 2-channel PGA with selectable gains from 1 to 128, supporting one differential input (AIN1±) and one single-ended input (AIN2).

It integrates two matched 200 µA RTD excitation current sources (RTD1/RTD2) with ±1% initial matching and 3 ppm/°C drift matching, enabling precise 3-wire and 4-wire RTD configurations. Calibration is supported via self-, system-, and background modes, with read/write access to on-chip calibration registers over a bidirectional serial interface (SCLK, SDATA, RFS, TFS).

Key Specifications

Pinout & Package

The AD7711AQ is housed in a 24-lead CERDIP (Q-24) package, hermetically sealed for extended temperature operation (–40°C to +85°C). Pin assignments match the standard AD7711 pinout defined in Rev. G datasheet Figure 12.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7714BN and ADS1248IPWR, the AD7711AQ uniquely combines internal 2.5 V reference, dual 200 µA RTD sources, and 2-channel flexibility in a CERDIP package - making it optimal for space-constrained, high-accuracy RTD transmitters requiring minimal external components.

Availability

AD7711AQ is available at Aetrix Electronics and suitable for RTD transducer interfaces, smart industrial transmitters, and portable process analyzers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7711AQ 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.

The AD7711AQ belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for high-accuracy, low-frequency measurement applications including RTD, thermocouple, and bridge sensor signal conditioning.

FAQ

What is the operating temperature range of the AD7711AQ?

The AD7711AQ is rated for operation from –40°C to +85°C, as specified in the Analog Devices AD7711 ordering guide for the Q-24 CERDIP package. This extended commercial temperature range supports deployment in harsh industrial environments such as factory automation and process control cabinets where ambient temperatures exceed standard commercial limits. The AD7711AQ maintains its 24-bit no-missing-codes performance and ±0.0015% INL specification across this full range when used with appropriate gain and filter settings.

Does the AD7711AQ include an internal voltage reference?

Yes, the AD7711AQ integrates a precision 2.5 V bandgap reference with ±1% initial tolerance at 25°C and 20 ppm/°C typical drift. This reference is available at the REF OUT pin and can be used directly as the ADC's reference or as a system-level bias voltage. When using the internal reference, the REF IN(+) and REF IN(–) pins must be configured accordingly - typically REF IN(+) tied to REF OUT and REF IN(–) to AGND - to achieve specified 24-bit performance without external components.

How does the AD7711AQ support 3-wire RTD measurements?

The AD7711AQ supports 3-wire RTD measurements using its dual 200 µA current sources (RTD1 and RTD2) and differential input AIN1(±). One current source drives the RTD through one lead, while the second source injects matching current into the sense lead to cancel lead resistance voltage drop. This technique, combined with the differential measurement across AIN1(±), removes lead resistance error without requiring external switching or additional amplifiers - a capability confirmed in the AD7711 Rev. G datasheet Applications section and RTD Excitation Currents specification table.

Can the AD7711AQ operate from a single supply?

Yes, the AD7711AQ supports single-supply operation by tying the VSS pin to AGND. In this configuration, the analog inputs (AIN1±, AIN2) must remain above –30 mV relative to AGND for correct operation, and unipolar input ranges up to +VREF are supported. The device retains full functionality including RTD excitation, digital filtering, and calibration modes. Single-supply use is explicitly validated in the General Description and Power Requirements sections of the AD7711 Rev. G datasheet.

What serial interface protocol does the AD7711AQ use?

The AD7711AQ uses a proprietary 3-wire synchronous serial interface with active-low frame synchronization (RFS for reads, TFS for writes), bidirectional SDATA, and configurable SCLK (input or output depending on MODE pin state). It does not implement SPI, I²C, or UART protocols. Communication requires precise timing aligned to the master clock (MCLK IN), with setup/hold times defined in the Timing Characteristics tables (e.g., t24 = 4 × tCLK IN max for RFS-to-data-valid delay). All register accesses are 24-bit wide, and the interface is fully documented in the Control Register and Timing Characteristics sections of the AD7711 Rev. G datasheet.