Analog Devices Inc. AD7705BR

Overview

AD7705BR from Analog Devices is a 16-bit sigma-delta analog-to-digital converter with two fully differential input channels, programmable gain (1–128), 3-wire SPI-compatible serial interface, and operation at 2.7–3.3 V or 4.75–5.25 V. It delivers 0.003% nonlinearity, <600 nV rms noise, and 1 mW max power dissipation at 3 V - enabling direct transducer interfacing in low-power industrial sensor systems.

For engineers reviewing the AD7705BR datasheet, AD7705BR pinout, AD7705BR application, or AD7705BR equivalent, key selection criteria include its dual-channel differential architecture, on-chip calibration support, selectable filter notch frequencies (20–60 Hz), unipolar/bipolar input range flexibility, and compatibility with microcontroller-based data acquisition where minimal external signal conditioning is required.

Technical Context

The AD7705BR employs a charge-balancing sigma-delta modulator followed by an on-chip digital filter with programmable first-notch frequency, enabling rejection of 50/60 Hz line interference. Its analog front end integrates a programmable-gain amplifier (PGA) and optional input buffer, supporting input ranges from ±10 mV to ±2.5 V depending on reference voltage and gain setting.

It uses a 3-wire serial interface (CS, SCLK, DIN/DOUT) compatible with SPI, QSPI, and MICROWIRE protocols, with Schmitt-triggered SCLK for noise immunity. The device supports self-calibration and system calibration to eliminate offset and full-scale errors, and operates in standby mode with ≤8 μA current at 3 V.

Key Specifications

Pinout & Package

AD7705BR is available in 16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages. Pin functions are identical across all variants.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7706BR, AD7705BR provides superior common-mode rejection for true differential sensor interfaces; compared with ADS1115IDGSR, it offers deterministic timing, integrated filtering, and calibration - making AD7705BR optimal for metrology-grade industrial sensing where noise, drift, and interference rejection are critical.

Availability

AD7705BR is available at Aetrix Electronics and suitable for pressure measurement, temperature monitoring, smart transmitter design, and battery voltage monitoring requiring stable component supply, long-lifecycle support, and guaranteed authenticity.

Supply support for AD7705BR 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 AD7705BR belongs to Analog Devices' precision sigma-delta ADC product line, engineered specifically for low-frequency, high-accuracy measurement applications where resolution, noise, and line-frequency rejection are paramount - such as sensor signal conditioning in harsh industrial environments.

FAQ

What is the maximum sampling rate of the AD7705BR?

The AD7705BR does not use traditional Nyquist sampling. Its output data rate depends on the selected digital filter notch frequency and PGA gain. With a 2.4576 MHz master clock and gain = 1, the maximum update rate is approximately 16.7 Hz (for 60 Hz notch) or 20 Hz (for 50 Hz notch). Higher gains reduce the effective rate - e.g., gain = 128 yields ~0.13 Hz. This behavior is inherent to its sigma-delta architecture and is documented in the AD7705BR timing specifications table.

Does the AD7705BR support both unipolar and bipolar input configurations?

Yes, the AD7705BR supports both unipolar and bipolar input modes via the B/U bit in the setup register. In unipolar mode (B/U = 1), it accepts 0 mV to +V_REF/gain; in bipolar mode (B/U = 0), it accepts ±V_REF/gain. For example, with V_REF = 2.5 V and gain = 16, unipolar range is 0–156.25 mV and bipolar range is ±156.25 mV. These ranges are explicitly defined in the AD7705BR datasheet Section "AIN Differential Voltage Range".

Can the AD7705BR operate with a 3.3 V supply and still achieve full 16-bit performance?

Yes, the AD7705BR is fully specified for operation from 2.7 V to 3.3 V. At 3 V supply with 1.225 V reference, it maintains 16-bit no-missing-codes performance, ±0.003% INL, and <600 nV rms noise. Power dissipation remains ≤1 mW, and standby current stays ≤8 μA. All static and dynamic specifications in the AD7705BR datasheet include 3 V test conditions - confirming full performance compliance across the entire 2.7–3.3 V range.

How does the AD7705BR handle reference voltage accuracy requirements?

The AD7705BR requires a stable, low-noise reference voltage - typically 1.225 V (for 3 V operation) or 2.5 V (for 5 V operation) - with ±1% tolerance for specified performance. Its differential reference inputs (REF IN(+) and REF IN(−)) reject common-mode noise, and ratiometric operation is supported when the reference and sensor excitation share the same source. Reference accuracy directly limits overall system gain error, so high-stability references like the ADR3412 or REF192 are recommended for metrology-grade use of the AD7705BR.

Is the AD7705BR pin-compatible with newer Analog Devices ADCs like the AD7124 series?

No, the AD7705BR is not pin-compatible with the AD7124 series. The AD7124-4/8 uses a 24-pin TSSOP or LFCSP package with different pin assignments, additional features (e.g., burn-out currents, GPIOs), and a distinct register map. While both are sigma-delta ADCs targeting precision measurement, the AD7124 series introduces enhanced diagnostics, flexible power modes, and higher integration - but requires PCB redesign and firmware updates. Migration from AD7705BR to AD7124 must be treated as a new design, not a drop-in replacement.