Texas Instruments ADS8684AIDBT

Overview

ADS8684AIDBT from Texas Instruments is a 16-bit, 4-channel, single-supply SAR analog-to-digital converter with integrated analog front-end, ±20 V input overvoltage protection, 500 kSPS aggregate throughput, and software-programmable bipolar/unipolar input ranges up to ±10.24 V - deployed in industrial PLC analog input modules for high-precision sensor signal digitization.

For engineers reviewing the ADS8684AIDBT datasheet, ADS8684AIDBT pinout, ADS8684AIDBT application, or ADS8684AIDBT equivalent, key selection criteria include channel-independent gain configuration, 1 MΩ constant input impedance across all ranges, SPI-compatible daisy-chain interface, ALARM output with per-channel thresholds, and operation across –40°C to 125°C industrial temperature range.

Technical Context

The ADS8684AIDBT implements a successive approximation register (SAR) ADC core with on-chip 4.096-V reference, integrated PGA, 4-channel multiplexer with auto/manual scan modes, and independent programmable input ranges per channel. It supports true bipolar inputs (±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V) and unipolar inputs (0–10.24 V, 0–5.12 V, 0–2.56 V, 0–1.28 V).

Each channel features 1-MΩ resistive input impedance, second-order LPF, OVP circuitry rated to ±20 V (with AVDD = 5 V), and auxiliary input (AUX_IN/AUX_GND). The device uses a 38-pin TSSOP package and communicates via a 4-wire SPI interface supporting daisy-chain topology with CS, SCLK, SDI, and SDO signals.

Key Specifications

Pinout & Package

The ADS8684AIDBT is housed in a 38-pin TSSOP (DBT) package measuring 9.7 mm × 4.4 mm, optimized for compact industrial PCB layouts with thermal performance characterized by R_θJA = 68.8°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADS8688AIDBT, the ADS8684AIDBT reduces channel count and pin utilization while retaining identical performance, power, and feature set - making it optimal for cost-sensitive 4-channel systems. Against AD7606BSTZ, it delivers greater design autonomy via integrated reference, OVP, and programmable ranges, but requires SPI-based host firmware adaptation.

Availability

ADS8684AIDBT is available at Aetrix Electronics and suitable for power automation, protection relay, and PLC analog input module designs requiring stable component supply, long-term industrial lifecycle support, and guaranteed traceable sourcing.

Supply support for ADS8684AIDBT 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 connectivity technologies for industrial, automotive, and communications markets.

The ADS8684A belongs to TI's precision data acquisition portfolio, designed specifically for ruggedized industrial systems demanding high dc accuracy, wide input voltage tolerance, and seamless integration into modular I/O architectures.

FAQ

What input voltage ranges does the ADS8684AIDBT support per channel?

The ADS8684AIDBT supports eight software-programmable input ranges per channel: bipolar options of ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, and ±0.64 V; and unipolar options of 0–10.24 V, 0–5.12 V, 0–2.56 V, and 0–1.28 V. Each channel can be independently configured, allowing mixed-range acquisition within a single ADS8684AIDBT device without external hardware changes.

How does the ADS8684AIDBT handle overvoltage conditions on its analog inputs?

The ADS8684AIDBT provides robust ±20 V input overvoltage protection on all AIN pins when AVDD = 5 V and source impedance is <30 kΩ. This protection is implemented internally using integrated clamp circuitry, eliminating the need for external TVS diodes or series resistors in most industrial surge environments. The device continues normal operation after fault removal without latch-up or calibration shift.

Can the ADS8684AIDBT operate with an external reference instead of the internal 4.096-V reference?

Yes, the ADS8684AIDBT supports external reference operation. When REFSEL is driven high, the REFIO pin becomes an input accepting an external reference voltage between 4.046 V and 4.146 V. The internal reference is disabled, and the ADC uses the externally applied voltage for conversion. This mode is used when higher initial accuracy or custom reference voltage is required beyond the internal 4.096-V ±0.025% specification.

What is the purpose of the ALARM pin on the ADS8684AIDBT?

The ALARM pin on the ADS8684AIDBT is an active-high, open-drain output that asserts when any enabled channel exceeds its individually programmed high threshold or falls below its low threshold. It serves as a hardware interrupt to notify the host controller of out-of-bounds conditions without polling, enabling rapid response in protection relay and safety-critical monitoring applications. Thresholds are stored in dedicated configuration registers and updated dynamically.

Does the ADS8684AIDBT require separate analog and digital ground planes on the PCB?

Yes, the ADS8684AIDBT requires physically separated analog (AGND) and digital (DGND) ground planes connected at a single point near the device. The datasheet specifies distinct AGND pins (pins 8, 28, 29, 31, 32) and one DGND pin (pin 33), with recommended decoupling: 0.1-µF ceramic capacitors from AVDD to AGND and DVDD to DGND, plus bulk capacitance on AVDD/DVDD. Improper grounding causes increased noise and degraded SNR performance.