Analog Devices Inc. AD688BQ

Overview

AD688BQ from Analog Devices is a high-precision monolithic ±10 V tracking voltage reference IC featuring laser-trimmed buried Zener core, dual Kelvin-output buffer amplifiers (A3/A4), and integrated ground-sense amplifier (A2). It delivers 2 mV initial output error, 1.5 ppm/°C drift over −40°C to +85°C, 6 µV p-p low-frequency noise, and supports precision calibration via GAIN ADJ and BAL ADJ pins. It serves as system-level reference in 12-bit+ data acquisition systems requiring absolute accuracy without trimming.

For engineers reviewing the AD688BQ datasheet, AD688BQ pinout, AD688BQ application, or AD688BQ equivalent, key selection criteria include tracking error ≤±1.5 mV, Kelvin force/sense capability for load regulation, noise filtering via NOISE REDUCTION pin, and compatibility with bipolar bridge driver topologies requiring matched ±10 V rails.

Technical Context

The AD688BQ integrates a proprietary ion-implanted buried Zener diode with laser-trimmed thin-film resistors to achieve <±2 mV initial error and <±1.5 mV tracking error. Its architecture includes four internal amplifiers: A1 generates a precision 20 V span, A2 provides Kelvin ground sensing, and A3/A4 deliver buffered ±10 V outputs with force/sense terminals.

Each output uses dedicated force and sense connections enabling true Kelvin regulation-eliminating wire-drop errors in long-line or high-current loads. The GAIN ADJ (Pin 5) and BAL ADJ (Pin 12) terminals allow independent trimming of span magnitude and center-point symmetry without degrading temperature stability.

Key Specifications

Pinout & Package

AD688BQ is housed in a 16-lead CERDIP (Q-16) package with 0.300-inch wide body, ceramic hermetic construction, and through-hole mounting. Pin layout supports full Kelvin routing, unbuffered reference taps (VHIGH/VLOW), and dedicated ground-sense input (GND SENSE +IN).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision voltage reference applications.

Compared with AD588BQ and REF5025ID, the AD688BQ uniquely delivers matched ±10 V tracking outputs with Kelvin force/sense, on-chip ground sensing, and dual trimming capability - making it the only option for precision bipolar signal chains requiring guaranteed symmetry and load regulation.

Availability

AD688BQ is available at Aetrix Electronics and suitable for high-accuracy data acquisition, bipolar bridge sensor excitation, and calibration-free test equipment requiring stable component supply across extended temperature ranges.

Supply support for AD688BQ 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, headquartered in Norwood, MA, with design centers worldwide.

The AD688BQ belongs to Analog Devices' precision voltage reference product line, engineered specifically for applications demanding absolute accuracy, low drift, and matched bipolar outputs in industrial, test & measurement, and aerospace systems.

FAQ

What is the maximum load current supported by each output of the AD688BQ?

The AD688BQ buffer amplifiers A3 and A4 each support ±10 mA continuous output current. This allows direct driving of multiple 12-bit+ ADCs, DACs, or op-amp inputs without external boosters. Load regulation remains within ±50 µV/mA for both +10 V and −10 V outputs across the full −40°C to +85°C range, ensuring stable reference performance under dynamic loading conditions typical in data acquisition systems.

How does the AD688BQ achieve ±10 V tracking accuracy better than discrete solutions?

The AD688BQ achieves ≤±1.5 mV tracking error through monolithic integration of a laser-trimmed buried Zener reference with matched thin-film resistor dividers and thermally coupled buffer amplifiers A3 and A4. Unlike discrete implementations, this co-location minimizes thermal gradients and process variation between positive and negative output paths - a key factor in maintaining symmetry across temperature and time without external matching components.

Can the AD688BQ be used without connecting the GAIN ADJ and BAL ADJ pins?

Yes - the AD688BQ is fully functional with GAIN ADJ (Pin 5) and BAL ADJ (Pin 12) left unconnected (floating). These pins are optional for fine calibration: the device meets all specifications - including ±2 mV initial error and ±1.5 mV tracking error - without any trimming. Floating the pins introduces no performance penalty and preserves the specified 1.5 ppm/°C drift and 6 µV p-p noise performance.

What is the purpose of the NOISE REDUCTION pin (Pin 7) on the AD688BQ?

The NOISE REDUCTION pin (Pin 7) connects to the internal Zener bias node and enables external broadband noise filtering. Connecting a 1 µF capacitor from Pin 7 to ground forms a low-pass filter with the internal 5 kΩ resistor, reducing 1 MHz noise from 840 µV p-p to ~250 µV p-p. This feature is especially valuable in high-resolution measurement systems where reference noise directly limits effective resolution, such as 20-bit+ delta-sigma ADC applications.

Does the AD688BQ require external capacitors for stability when driving capacitive loads?

Yes - the AD688BQ's A3 and A4 outputs may oscillate when driving >1000 pF capacitive loads. For stable operation, use the recommended compensation network: a 150 Ω series resistor isolating the load, a 10 kΩ DC feedback path to preserve accuracy, and a 1 µF capacitor across the feedback path. This configuration maintains full DC accuracy while suppressing ringing and ensuring <2 µs settling for step loads - critical for shared reference buses in multi-ADC systems.