Analog Devices Inc. AD977CN

Overview

AD977CN from Analog Devices is a 16-bit, 100 kSPS successive-approximation ADC operating from a single 5 V supply, featuring internal 2.5 V reference, ±10 V/0 V–5 V input ranges, and high-speed serial interface in a 20-lead SOIC package. It delivers ±3 LSB INL, 83 dB SNR, and 100 mW max power dissipation for precision data acquisition in industrial process control and test equipment.

For engineers reviewing the AD977CN datasheet, AD977CN pinout, AD977CN application, or AD977CN equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, application-specific implementation guidance, and two confirmed alternative parts with documented functional and layout implications.

Technical Context

The AD977CN implements a factory-calibrated switched-capacitor SAR architecture with on-chip clock generation and dual-mode serial interface (internal or external DATACLK). Its conversion control relies on R/C and CS signals, with BUSY indicating active conversion cycles and pipeline delay ensuring results are only available post-conversion.

It supports both binary two's complement and straight binary output formats via SB/BTC, and offers flexible reference configuration-either internal 2.5 V (±2 mV drift) or external 2.3 V–2.7 V-with dedicated CAP and REF pins requiring 2.2 µF tantalum decoupling. Power-down mode reduces consumption to 50 µW while retaining last conversion result.

Key Specifications

Pinout & Package

AD977CN is packaged in a 20-lead skinny SOIC (SOIC_N) with 0.3" body width and standard 0.050" lead pitch. Pin 1 is marked with a dot; pin numbering follows JEDEC MS-013AA outline.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 16-bit SAR ADC applications.

Compared with AD977CN, AD974CN trades 2 bits of resolution and internal reference for lower cost and identical footprint, while ADS8320U offers SPI compatibility and smaller package at the expense of missing bipolar range support and daisy-chain capability.

Availability

AD977CN is available at Aetrix Electronics and suitable for industrial process control, automated test equipment, and environmental data logging requiring stable component supply, long-lifecycle availability, and guaranteed traceable sourcing.

Supply support for AD977CN 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, communications, automotive, and healthcare markets since 1965.

The AD977 product line delivers precision 16-bit SAR ADCs optimized for high-accuracy, low-power data acquisition in harsh environments-designed specifically for applications demanding factory-calibrated DC accuracy and robust AC performance without external calibration.

FAQ

What is the maximum input frequency the AD977CN can accurately digitize?

The AD977CN has a full-power bandwidth of 700 kHz and a –3 dB input bandwidth of 1.5 MHz. For accurate digitization without amplitude loss, input signals should be limited to ≤700 kHz when operating at full scale. This ensures Signal-to-(Noise+Distortion) remains ≥83 dB and avoids aliasing in systems using anti-aliasing filters aligned to the Nyquist criterion. The AD977CN achieves this performance using its switched-capacitor SAR architecture with 40 pF sampling capacitance and aperture delay of 40 ns.

Does the AD977CN require an external reference, or does it include one?

The AD977CN includes a factory-trimmed internal 2.5 V reference with ±2 mV initial tolerance and ±2 ppm/°C drift-fully specified for ±0.5% full-scale accuracy. External reference is optional and supported via the REF pin (2.3 V–2.7 V range), but not required. When using the internal reference, a 2.2 µF tantalum capacitor must be placed between CAP and AGND1 to ensure stability. This integrated reference eliminates BOM cost and layout complexity compared to external solutions.

How does the AD977CN handle power-down mode, and what happens to the conversion result?

In power-down mode (PWRD = HIGH), the AD977CN reduces power dissipation to 50 µW and halts new conversions, but retains the last valid conversion result in its internal shift register. Upon exit from power-down (PWRD = LOW), the device resumes normal operation within 1 ms-no recalibration or reinitialization is needed. The stored result remains accessible via serial interface, enabling wake-on-event architectures where the host reads prior measurement immediately after wake-up. This behavior is explicitly guaranteed in the datasheet's Recovery to Rated Accuracy specification.

Can the AD977CN interface directly with an FPGA or microcontroller without level-shifting?

Yes-the AD977CN uses standard 5 V CMOS logic levels: VIH ≥ 2.0 V and VIL ≤ 0.8 V, with VOL ≤ 0.4 V (ISINK = 1.6 mA) and VOH ≥ 4.0 V (ISOURCE = 500 µA). It is fully compatible with 5 V microcontrollers (e.g., legacy 8051, PIC18F) and 5 V-tolerant FPGA I/O banks. No level-shifting is required. However, proper decoupling (0.1 µF ceramic + 2.2 µF tantalum per supply) and ground separation (AGND1/AGND2/DGND) must be maintained to preserve 16-bit accuracy and avoid digital noise coupling into analog sections.

What are the key layout recommendations for achieving specified AC performance with the AD977CN?

To achieve the AD977CN's rated 83 dB SNR and –90 dB THD, follow these layout practices: (1) Use separate AGND1 (reference), AGND2 (analog core), and DGND planes tied at single point near CAP/REF decoupling; (2) Place 2.2 µF tantalum capacitors directly between CAP–AGND1 and REF–AGND2 with minimal trace length; (3) Route analog inputs (R1IN/R2IN/R3IN) away from digital traces (DATACLK/DATA/SYNC); (4) Keep VANA and VDIG supplies independently decoupled with 0.1 µF ceramic + 2.2 µF tantalum each; (5) Avoid vias under the AD977CN body to preserve thermal and ground integrity.