AD7851KNZ

Overview

The AD7851KNZ is a 14-bit, high-speed serial analog-to-digital converter (ADC) manufactured by Analog Devices Inc. It operates from a single 5 V supply and supports a throughput rate of 285 kSPS at temperatures ranging from 0 °C to +85 °C. The device features a pseudo-differential input architecture with two selectable voltage ranges: 0 V to VREF and ±VREF/2. It incorporates self-calibration and system calibration capabilities to maintain accuracy over time and temperature variations. The ADC utilizes a successive approximation register (SAR) structure and offers flexible serial interface compatibility with SPI, QSPI, 8051, and microprocessor systems. Typical power consumption is 60 mW in normal mode, with a low-power sleep mode consuming approximately 5 µW.

Feature Summary

• Supports self-calibration and system calibration with autocalibration on power-up to ensure long-term accuracy.
• Features a pseudo-differential input scheme with two configurable input voltage ranges for versatile signal interfacing.
• Provides flexible serial interface options compatible with standard protocols including SPI, QSPI, and 8051.
• Includes multiple power-down modes to minimize energy consumption in battery-operated applications.

Applications

• Digital Signal Processing
• Speech Recognition and Synthesis
• Spectrum Analysis
• DSP Servo Control
• Instrumentation and Control Systems

Procurement Notes

Verify the specific grade and package configuration when ordering, as the AD7851 series includes A and K grades with distinct linearity and throughput specifications. Confirm that the KNZ suffix corresponds to the SOIC-24 package variant if required for your PCB layout. Ensure that the operating temperature range aligns with your system requirements, as the K grade is specified for commercial temperatures. Cross-reference the datasheet revision to confirm pinout and electrical characteristics match your design constraints.

Selection Notes

Select the AD7851KNZ when a 14-bit resolution and 285 kSPS sampling rate are sufficient for the application within the 0 °C to +85 °C temperature range. Consider this component if the design requires a single 5 V supply and pseudo-differential inputs to simplify front-end circuitry. Evaluate the need for internal calibration features to reduce external precision components. Compare against higher-speed or higher-resolution alternatives if the 333 kSPS A-grade performance or 16-bit resolution is necessary for stricter dynamic performance requirements.

Part Context

The AD7851 is part of Analog Devices' high-speed serial ADC family, designed for applications requiring moderate resolution and speed with low power consumption. It competes in the market for general-purpose data acquisition systems where cost-effective, single-supply operation is prioritized. The device shares architectural similarities with other SAR ADCs but distinguishes itself through integrated calibration and flexible digital interface options. It serves as a bridge between analog sensor signals and digital processing units in embedded systems.

Replacement Considerations

Direct replacements include the AD7851AN (PDIP package), AD7851AR (SOIC package), and AD7851KR (SOIC package). Verify that substitute parts match the required package type and thermal characteristics. Ensure that the replacement grade (A or K) meets the throughput and linearity specifications of the original design. Check for any differences in calibration algorithms or interface timing requirements when migrating between package variants or grades.

FAQ

What is the difference between the A and K grades of the AD7851?

The A grade guarantees a throughput rate of 333 kSPS with ±2 LSB integral nonlinearity error, while the K grade guarantees 285 kSPS with ±1 LSB integral nonlinearity error. Both grades are guaranteed to operate up to 125 °C at a reduced throughput of 238 kSPS.

How does the AD7851 handle calibration?

The AD7851 features both self-calibration and system calibration options. Self-calibration corrects internal errors such as offset and gain drift. System calibration allows the user to adjust for external circuit errors. Calibration data can be read and written via the serial interface, and autocalibration occurs automatically upon power-up.

What are the available analog input voltage ranges?

The AD7851 supports two input ranges selected by the AMODE pin. Range 0 is unipolar, from 0 V to VREF. Range 1 is bipolar, from -VREF/2 to +VREF/2, centered about VREF/2. The negative input (AIN-) can be biased to accommodate these ranges.