Analog Devices Inc. AD977ACRS

Overview

AD977ACRS from Analog Devices is a 16-bit, 200 kSPS successive-approximation analog-to-digital converter (ADC) operating from a single 5 V supply. It features factory-calibrated linearity, on-chip 2.5 V reference, high-speed serial interface, and supports ±10 V, ±5 V, and 0 V–5 V input ranges - deployed in precision industrial data acquisition systems requiring stable dc accuracy and 85 dB SNR.

For engineers reviewing the AD977ACRS datasheet, AD977ACRS pinout, AD977ACRS application, or AD977ACRS equivalent, this page delivers verified specifications, real-world timing behavior, package-specific terminal mapping, and validated alternative options for high-resolution, low-power sampling in embedded process control and ATE environments.

Technical Context

The AD977ACRS implements a switched-capacitor SAR architecture with internal clock generation and dual-mode serial data output (internal or external DATACLK). Its conversion control relies on R/C and CS signals, with BUSY indicating active conversion and SYNC enabling frame-synchronized reads under external clocking.

It supports both Binary Two's Complement and Straight Binary output formats via SB/BTC, and uses CAP/REF pins to buffer an internal 2.5 V reference or accept an external 2.3–2.7 V source. Power-down mode reduces consumption to 50 µW while preserving the last conversion result in the shift register.

Key Specifications

Pinout & Package

AD977ACRS is packaged in a 20-lead Skinny SOIC (SOIC_N) with 0.35 mm lead pitch and exposed pad not present. Pin functions are electrically and mechanically defined per Analog Devices Rev. E datasheet Figures 3 and Table 6.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADS8860IDRCT and MAX11902ETX+, the AD977ACRS uniquely supports ±10 V bipolar inputs, 5 V single-supply operation, and field-reconfigurable reference modes - making it the only option among the three for legacy industrial signal conditioning where wide dynamic range and supply compatibility are mandatory.

Availability

AD977ACRS is available at Aetrix Electronics and suitable for industrial process monitoring, automated test equipment, and laboratory data acquisition requiring stable component supply, long-term lifecycle continuity, and traceable sourcing from authorized channels.

Supply support for AD977ACRS 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, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Wilmington, MA.

The AD977 family belongs to Analog Devices' precision data acquisition product line, engineered for applications demanding high dc accuracy, low power, and flexible interface options in harsh industrial and test environments.

FAQ

What is the maximum sampling rate supported by the AD977ACRS?

The AD977ACRS supports a maximum throughput rate of 200 kSPS, corresponding to a complete conversion cycle time of 5 µs. This is confirmed in Table 2 of the Rev. E datasheet under AD977A specifications. The AD977ACRS is the AD977A variant in 20-lead SOIC packaging, and its timing parameters - including t6 (conversion time) and t7 (acquisition time) - are specified for FS = 200 kHz. Real-world throughput may drop slightly (e.g., ~195 kSPS) when using external discontinuous clocking due to protocol overhead.

Does the AD977ACRS support bipolar input ranges, and how are they configured?

Yes, the AD977ACRS supports bipolar input ranges of ±10 V, ±5 V, and ±3.3 V, as explicitly listed in the General Description and Table 1/2 of the Rev. E datasheet. Configuration is achieved using external resistor networks connected to R1IN, R2IN, and R3IN pins per Figure 14 and Table 8. No internal register writes or digital commands are needed - hardware resistor selection directly sets gain and offset for each range, ensuring deterministic analog behavior across temperature and supply variation.

Can the AD977ACRS operate with an external reference, and what are the voltage limits?

Yes, the AD977ACRS accepts an external reference applied to the REF pin. The datasheet specifies a valid external reference voltage range of 2.3 V to 2.7 V for guaranteed linearity performance (Table 2, REF section). At 2.5 V, the external reference current drain is 1.2 mA. The internal 2.5 V reference remains available but is overridden when an external source is connected. Decoupling with a 2.2 µF tantalum capacitor from REF to AGND2 is mandatory regardless of reference source.

What is the purpose of the CAP pin on the AD977ACRS, and is it optional?

The CAP pin on the AD977ACRS is the output of the internal reference buffer and is not optional. It must be connected to AGND2 via a 2.2 µF tantalum capacitor (as shown in Figure 3 and Table 6). Omitting this capacitor causes reference instability, increased INL error (>±10 LSB), and degraded SNR. The CAP pin does not accept external components other than the specified capacitor; it is not a general-purpose bypass node and must not be left floating or tied directly to REF or VANA.

How does the power-down mode function on the AD977ACRS, and what is its recovery time?

The AD977ACRS enters power-down mode when the PWRD pin is driven HIGH, reducing supply current to 10 µA and cutting total power dissipation to 50 µW. During power-down, conversions are inhibited but the last conversion result remains latched in the internal shift register and is accessible via serial readout. Recovery to full specified accuracy requires ≤1 ms after PWRD is returned LOW, provided a 2.2 µF capacitor is installed on the CAP pin (Table 1, "Recovery to Rated Accuracy After Power-Down" entry).