Texas Instruments ADS821U

Overview

ADS821U from Texas Instruments is a monolithic 10-bit, 40MHz pipeline analog-to-digital converter with internal track-and-hold, internal ±1.25V/±3.25V reference, and TTL/HCT-compatible CMOS outputs. It operates from a single +5V supply, supports differential or single-ended inputs, and delivers 58dB SNR and ±0.5 LSB typical DNL for high-fidelity video and imaging digitization.

For engineers reviewing the ADS821U datasheet, ADS821U pinout, ADS821U application, or ADS821U equivalent, this page provides verified technical context, SO-28 package mapping, real-world timing and dynamic performance data, and validated alternative options for video digitizing, ultrasound imaging, CCD systems, and IF/baseband sampling applications.

Technical Context

The ADS821U implements a 9-stage pipelined architecture with 2-bit quantizers per stage and digital error correction logic to guarantee no missing codes and ±0.5 LSB DNL at 40MHz. Its fully differential track-and-hold accepts ±1.25V to ±3.25V input range centered at +2.25V common-mode voltage, enabling high-SNR acquisition of fast transient signals.

Conversion is clocked on both edges of a 50% duty-cycle CMOS input (CLK), with 6.5-cycle latency and aperture jitter of 7ps rms. Output coding is selectable between Straight Offset Binary (SOB) and Binary Two's Complement (BTC) via MSBI pin, while OE enables 3-state output control for bus interfacing.

Key Specifications

Pinout & Package

ADS821U is housed in a 28-pin SOIC (SO-28) package with 0.6 mm lead pitch and standard JEDEC MO-012AC outline. Pin 1 is located at the top-left corner adjacent to the index mark; pins are numbered counter-clockwise.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-speed ADC applications.

Compared with ADS821U, ADS820U offers identical speed and resolution but reduced thermal qualification, while AD9203ARUZ trades internal reference and track-and-hold integration for lower voltage and power-making ADS821U the preferred choice for +5V systems needing plug-and-play analog front-end simplicity in demanding imaging applications.

Availability

ADS821U is available at Aetrix Electronics and suitable for video digitizing, ultrasound imaging, and CCD-based scanning applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ADS821U 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and high-performance data converters for industrial, automotive, and communications markets.

The ADS821U belongs to TI's high-speed precision ADC product line, designed specifically for demanding imaging, instrumentation, and communications systems requiring guaranteed linearity, low jitter, and robust single-supply operation.

FAQ

What is the maximum sampling rate supported by the ADS821U?

The ADS821U supports a maximum sampling rate of 40 million samples per second (40 MSPS), as specified across its full operating temperature range of –40°C to +85°C. This rate is achievable with a 50% duty-cycle CMOS clock having <2 ns rise/fall time and proper power supply decoupling. At this rate, the device maintains 58 dB SNR and ±0.5 LSB DNL performance, making it suitable for real-time video and ultrasound digitization tasks where timing fidelity is critical. The ADS821U datasheet confirms this specification under "CONVERSION CHARACTERISTICS" with t_CONV ≤ 25 ns.

Does the ADS821U include an internal reference and track-and-hold circuit?

Yes, the ADS821U integrates both an internal reference and a track-and-hold (T&H) circuit. Its internal reference provides +1.25V (REFB) and +3.25V (REFT) rails, establishing a 4 V_p-p differential full-scale input range centered at +2.25V common-mode voltage. The fully differential T&H supports both differential and single-ended inputs and is optimized for low aperture jitter (7 ps rms). These integrated functions eliminate the need for external reference ICs or discrete T&H stages, reducing bill-of-materials and layout complexity in compact imaging systems.

What package type is used for the ADS821U?

The ADS821U is packaged in a 28-pin small-outline integrated circuit (SO-28) with JEDEC MO-012AC outline and 0.6 mm lead pitch. This surface-mount package features four dedicated GND and four +VS pins to minimize power distribution impedance and improve noise immunity at 40 MSPS operation. The SO-28 footprint is compatible with standard reflow soldering processes and widely supported in PCB design libraries. TI's official ordering information explicitly lists "SO-28" as the package for ADS821U in the PACKAGE/ORDERING INFORMATION table.

Can the ADS821U operate with a single +5V supply?

Yes, the ADS821U is designed to operate from a single +5V supply (specified range +4.75V to +5.25V). All analog and digital circuitry-including the internal reference, track-and-hold, pipeline quantizer, and CMOS output drivers-function correctly within this rail. No negative or auxiliary supplies are required. Power consumption is 380 mW typical at 40 MSPS, and thermal resistance θ_JA is 75°C/W, allowing operation without heatsinking in well-ventilated enclosures. This single-supply capability simplifies power architecture in video capture cards and portable medical devices.

How does the ADS821U handle digital output formatting and bus interfacing?

The ADS821U provides 10-bit parallel CMOS outputs (B1–B10) with selectable coding: Straight Offset Binary (SOB) by default (MSBI pin LOW or floating), or Binary Two's Complement (BTC) when MSBI is driven HIGH. Output enable (OE) controls 3-state operation-HIGH places outputs in high-impedance mode, enabling direct connection to shared data buses. Data latency is fixed at 6.5 clock cycles from CLK edge to valid output. These features allow seamless interfacing with FPGAs, microcontrollers, or DSPs without external latches or level translators, as confirmed in the "DIGITAL OUTPUT DATA" section of the SBAS040B datasheet.