Analog Devices Inc. AD7846JN

Overview of the AD7846JN 16-Bit DAC with Voltage Output

The AD7846JN from Analog Devices is a high accuracy, 16-bit digital-to-analog converter (DAC) featuring a voltage output and packaged in a 28-pin PDIP (plastic dual in-line package). Designed using Analog Devices’ LC²MOS process, the AD7846JN targets precision signal conversion for applications ranging from industrial automation control and data acquisition systems to precision instrumentation and automatic test equipment (ATE).

Main Characteristics of the AD7846JN

The AD7846JN delivers several critical features for engineers seeking reliable, high-resolution analog outputs:

True 16-bit monotonicity over temperature, ensuring precise digital-to-analog translations even under varying environmental conditions.

Very low total unadjusted error: ±2 LSB (least significant bit) integral nonlinearity, providing strong accuracy across the full scale.

Flexible output configuration, supporting both unipolar (0 to +5V, 0 to +10V) and bipolar (±5V, ±10V) ranges with internal or external references.

Built-in microprocessor-compatible parallel interface with readback capability, enabling efficient integration and system diagnostics.

Multiplying DAC capability for dynamic reference applications.

Low power dissipation: a typical 100 mW, making it suitable for dense, multi-channel systems.

Internal Structure and Operational Details of the AD7846JN

The AD7846JN employs a segmented 16-bit DAC architecture. The device organizes the four most significant bits (MSBs) for segment selection in a 16-resistor string; both segment taps are buffered and brought to a secondary 12-bit DAC, which interpolates between them. This approach combines the advantages of resistor-string stability for the MSBs and high-resolution interpolation, guaranteeing full 16-bit monotonic performance—a crucial parameter for closed-loop and precision applications.

The on-chip output amplifier, with configurable feedback, supports gains of 1 or 2, providing a range of output spans. Specific attention to the design of these amplifiers ensures tight matching and minimizes offset, a frequent source of nonlinearity in conventional structures.

Performance Metrics and Electrical Parameters of the AD7846JN

Operating over typical ±15V analog supplies and a +5V digital supply, the AD7846JN maintains stable performance for extended temperature ranges. Accuracy is specified as follows:

Integral nonlinearity: ±2 LSB maximum.

Full 16-bit monotonicity over temperature.

Output drive: capable of sourcing or sinking current into a 2 kΩ, 1000 pF load.

Low power: typical dissipation of 100 mW.

Input logic compatible with standard microprocessors.

AC performance supports fast settling with minimal digital-to-analog “glitch” energy, and digital feedthrough has been engineered to remain low—even under direct bus connection—through clever use of input latch structures.

Output Modes and Signal Levels of the AD7846JN

The AD7846JN’s versatility is evident in its support for both unipolar and bipolar outputs, as well as multiplying DAC operation:

Unipolar output: With a +5V reference and feedback configuration, the DAC can produce a 0V to +10V or 0V to +5V span, selectable via an external resistor connection.

Bipolar output: Using both +5V and -5V references (for example, from an AD588 precision reference), the DAC delivers ±10V or ±5V spans. This is especially valuable in instrumentation and process control where true zero crossing is necessary.

Multiplying mode: By applying dynamic or AC signals to the reference input, the AD7846JN serves as a digitally programmable gain element across four quadrants, supporting advanced waveform synthesis and control applications.

Microprocessor Connectivity and System Integration with the AD7846JN

Designed for straightforward integration, the AD7846JN offers a parallel interface with 16 data I/O lines and standard control signals (CS, R/W, LDAC, CLR). This enables high-speed updates and simultaneous multi-channel synchronization. The readback function allows software routines to verify the output code—a critical function for diagnostic and ATE environments.

Example microprocessor interfaces, such as to Intel 8086 and Motorola MC68000, are supported with reference designs, including double-buffering to efficiently update multiple DACs without transient artifacts. The device is also engineered to minimize digital feedthrough, with the option for additional bus isolation when required.

Practical Uses and Engineering Applications of the AD7846JN

The precision and flexibility of the AD7846JN make it suitable for a range of real-world applications:

ATE systems benefit from the device’s high accuracy, low noise, and readback capability, streamlining calibration and test workflows.

Industrial and process controllers leverage the bipolar output ranges and monotonicity to drive actuators, generate analog setpoints, or synthesize signals.

Position measurement systems, such as those employing LVDTs, exploit the fine control resolution and phase integrity of the DAC output.

Multiplying DAC applications include programmable gain control and dynamic waveform synthesis, with AC performance data supporting design at higher signal frequencies.

Design Factors Minimizing Noise, Grounding Strategies, and PCB Layout for the AD7846JN

High-resolution analog applications demand best-practice PCB layout and system grounding to preserve the AD7846JN’s low noise performance (LSB = 152 μV for a 10V output span). Careful partitioning of analog and digital grounds, minimizing parasitic track resistances, and strategic placement of sense points are recommended.

Standard layout guidance involves:

Isolating digital and analog return paths, especially for reference and output signals.

Using force/sense techniques for reference inputs to reduce error due to PCB trace resistance, particularly important at 16-bit resolutions.

Proper decoupling of supply lines and shielding, where necessary, to prevent digital logic noise from coupling into sensitive analog nodes.

Environmental Ratings and Reliability Figures for the AD7846JN

The AD7846JN is rated for industrial-grade temperature ranges (0°C to +70°C for J versions; -40°C to +85°C for A/B versions). Abs max ratings accommodate typical analog system voltages, with ESD precautions governing safe device handling and assembly. The device is available in plastic and ceramic DIP/PLCC/LCC packages for compatibility with a range of assembly and operating environments.

Available Packaging Types and Physical Dimensions of the AD7846JN

Supporting industry-standard footprints, the AD7846JN is offered in:

28-lead PDIP (N-28-2)

28-lead CERDIP (Q-28-2)

28-terminal LCC (E-28-1)

28-lead PLCC (P-28)

Dimensional drawings are referenced to JEDEC standards for straightforward PCB design and mechanical integration.

Possible Alternative or Replacement Devices for the AD7846JN

When selecting a replacement for the AD7846JN, engineers should consider key parameters like resolution, monotonicity, supply voltage compatibility, interface type, and available package options. Potential alternatives within the Analog Devices portfolio include:

AD7846KR: Same core function in different temperature grade/package.

AD669: A pin-compatible, 16-bit DAC with high accuracy, suitable for precision systems.

AD976/AD977: 16-bit DACs, variations in interface and output type may require minor board adjustments.

Additionally, products such as the DAC8800 series from Texas Instruments may be considered, assessing requirements for interface compatibility and supply voltage.

Conclusion

: Suitability of the AD7846JN for Precision Analog Applications

The Analog Devices AD7846JN stands out for its blend of high resolution, robust monotonicity, and integration-focused features. With its flexible output ranges, proven architecture, and comprehensive support for microprocessor interfaces, it is a solid foundation for precision analog output in demanding instrumentation, control, and test applications. By following the recommended noise, grounding, and layout practices, engineers can realize the full performance potential of the AD7846JN, ensuring reliable operation for years to come.