Texas Instruments ADS821U-1

Overview

ADS821U-1 from Texas Instruments is a monolithic 10-bit, 40MHz pipeline analog-to-digital converter with internal track-and-hold, on-chip +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 differential linearity at 500kHz for high-fidelity video digitizing and ultrasound imaging.

For engineers reviewing the ADS821U-1 datasheet, ADS821U-1 pinout, ADS821U-1 application, or ADS821U-1 equivalent, this page provides verified technical context, SO-28 package mapping, real-world timing and dynamic performance data, and two validated alternative ADCs for imaging and telecom signal chain design.

Technical Context

The ADS821U-1 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 500kHz. Its fully differential track-and-hold accepts ±1V differential input centered at +2.25V common-mode voltage, enabling direct interface with transformer-coupled or op-amp-driven sources.

Conversion is clocked on both edges of a 40MHz CMOS-level input (t_H/t_L ≥12.5ns), producing 10-bit SOB or BTC output after 6.5-cycle latency. Output drivers support 3-state control via OE and MSBI pins, with aperture jitter of 7ps RMS and over-voltage recovery in 2ns.

Key Specifications

Pinout & Package

ADS821U-1 is housed in a 28-pin SOIC (SO-28) package with 0.6mm lead pitch and exposed pad not present. Pin 1 is located at top-left corner when viewed from top with marking dot oriented left; pin count proceeds counter-clockwise.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADS821U-1, ADS820U trades half the sample rate and lower SFDR for 42% less power, while AD9203ARUZ offers better SNR but demands external support circuitry - making ADS821U-1 optimal for drop-in upgrades in legacy video and medical equipment.

Availability

ADS821U-1 is available at Aetrix Electronics and suitable for video digitizing, ultrasound imaging, and gamma camera systems requiring stable component supply and long-term industrial lifecycle support.

Supply support for ADS821U-1 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 and embedded processing technologies, with decades of expertise in high-performance data converters and signal chain solutions.

The ADS821U-1 belongs to TI's high-speed pipeline ADC product line, engineered specifically for demanding imaging, telecommunications, and instrumentation applications where speed, linearity, and low power coexist.

FAQ

What is the maximum sampling rate supported by the ADS821U-1?

The ADS821U-1 supports a maximum sampling rate of 40 million samples per second (40 MSPS), specified under conditions of +25°C ambient temperature, +5V supply, and a 50% duty cycle clock with ≤2ns rise/fall time. At this rate, it achieves full AC/DC performance including 58dB SNR and ±0.5 LSB differential linearity at 500kHz input frequency. The ADS821U-1 maintains functional operation down to 10kSPS for low-power monitoring modes.

Does the ADS821U-1 require external reference components?

No, the ADS821U-1 integrates internal +1.25V and +3.25V reference buffers, enabling immediate operation with only 0.1µF bypass capacitors on REFB (pin 21) and REFT (pin 23). External references are optional and only needed when adjusting full-scale range or improving gain drift; if used, they must drive ≥18mA and stay within +1.1V to +3.4V bounds. The ADS821U-1's internal reference eliminates BOM cost and layout complexity in set-top boxes and security cameras.

How does the ADS821U-1 handle differential versus single-ended analog inputs?

The ADS821U-1 natively supports differential inputs (pins 26 and 27) with ±1V swing around +2.25V common-mode voltage. For single-ended use, tie the complementary input (e.g., pin 27) to CM (pin 22), yielding a +0.25V to +4.25V unipolar range - though this increases even-order harmonics. The ADS821U-1's internal track-and-hold converts single-ended signals to differential internally, preserving performance when driven by op-amps like OPA694 or OPA860 as documented in TI's SBAS040B application notes.

What output data formats does the ADS821U-1 support?

The ADS821U-1 provides two selectable output coding formats: Straight Offset Binary (SOB) and Binary Two's Complement (BTC). SOB is the default (pin 19 LOW or floating), where full-scale input yields 1111111111. BTC is enabled by driving MSBI (pin 19) HIGH, inverting the MSB to produce 0111111111 at full scale. Both formats are delivered on pins B1–B10 as CMOS-level parallel data with 6.5-cycle latency, and outputs enter high-impedance state when OE (pin 18) is HIGH.

Is the ADS821U-1 pin-compatible with other members of the ADS82x family?

Yes, the ADS821U-1 shares identical SO-28 pinout and footprint with ADS820U and ADS822U, differing only in maximum sampling rate (20/40/60 MSPS) and dynamic performance. All three support the same +5V supply, internal reference, 10-bit parallel output, and OE/MSBI control logic. This allows direct replacement in existing layouts when upgrading sampling capability - for example, swapping ADS820U for ADS821U-1 in a video digitizer without PCB revision, provided thermal and clock integrity margins are verified.