Texas Instruments SN65ELT21DGKR

Overview

SN65ELT21DGKR from Texas Instruments is a 5-V PECL-to-TTL level translator in VSSOP-8 package, delivering 3 ns typical propagation delay, 24-mA TTL output drive, and deterministic low-level output under open or sub-1.3-V input conditions. It supports backplane data/clock transmission across industrial temperature range (–40°C to 85°C) with built-in temperature compensation.

For engineers reviewing the SN65ELT21DGKR datasheet, SN65ELT21DGKR pinout, SN65ELT21DGKR application, or SN65ELT21DGKR equivalent, this device serves as a drop-in alternative to MC10ELT21/MC100ELT21 for high-speed PECL signal interfacing in telecom clock distribution, FPGA I/O bridging, and legacy system upgrades requiring robust single-ended TTL output conversion.

Technical Context

The SN65ELT21DGKR implements a differential PECL input stage with internal 50-kΩ pull-down resistors and a dedicated VBB reference voltage output (3.62–3.74 V) for single-ended biasing or AC-coupled input termination. Its TTL output stage delivers rail-to-rail swing with VOH ≥ 2.4 V at –3 mA and VOL ≤ 0.5 V at 24 mA sink current.

It operates strictly on +5-V supply (4.2–5.7 V), requires no negative rail, and features deterministic logic behavior during input float or undervoltage - eliminating external bias networks. AC performance includes 200 MHz maximum switching frequency and <20 ps RMS random jitter over full temperature range.

Key Specifications

Pinout & Package

VSSOP-8 package (DGK), 3.0 mm × 3.0 mm body, 1.1 mm max height, 0.65 mm lead pitch, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PECL-to-TTL translation applications.

Compared with MC100ELT21DG and SN65LVEP11DGKR, the SN65ELT21DGKR uniquely combines +5-V single-supply operation, integrated VBB reference, and guaranteed low-output behavior on open inputs - making it optimal for cost-sensitive, thermally demanding industrial upgrades where supply simplification and reliability outweigh raw bandwidth needs.

Availability

SN65ELT21DGKR is available at Aetrix Electronics and suitable for telecom clock distribution, FPGA I/O bridging, industrial backplane data links, and legacy system upgrade interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN65ELT21DGKR 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, with decades of leadership in interface and signal conditioning ICs.

The SN65ELT21DGKR belongs to TI's high-speed interface translator product line, engineered specifically for reliable PECL-to-TTL signal conversion in industrial, telecom, and computing infrastructure where robustness, deterministic behavior, and drop-in replaceability are critical.

FAQ

What is the supply voltage requirement for SN65ELT21DGKR?

The SN65ELT21DGKR operates exclusively from a single +5-V supply, with specified range of 4.2 V to 5.7 V. It does not require a negative rail (VEE) or dual supplies. This simplifies power design compared to ECL-family translators like MC100ELT21, which need –5.2 V. All DC and AC specifications in the datasheet are validated across this VCC range and full temperature span (–40°C to +85°C).

How does SN65ELT21DGKR handle open or unterminated PECL inputs?

The SN65ELT21DGKR guarantees a deterministic low logic level at Q when either PECL input is open or falls below 1.3 V, thanks to internal 50-kΩ pull-down resistors. This eliminates the need for external biasing components and prevents metastability during power-up, hot-swap, or cable disconnect events - a key reliability feature absent in many competing translators.

What is the purpose and usage of the VBB pin on SN65ELT21DGKR?

The VBB pin on SN65ELT21DGKR provides a stable 3.62–3.74 V internal reference used to bias the unused PECL input in single-ended mode or terminate AC-coupled PECL signals. When used, a 0.01 µF capacitor must be placed between VCC and VBB, and total sink/source current must stay below ±0.5 mA. Leaving VBB unconnected is valid if unused - no external circuitry required.

Is SN65ELT21DGKR pin-compatible with MC10ELT21 or MC100ELT21?

Yes, SN65ELT21DGKR is explicitly documented as drop-in compatible with both MC10ELT21 and MC100ELT21 in function, pinout, and package (VSSOP-8 matches TSSOP-8). However, unlike those parts, SN65ELT21DGKR operates on +5-V only - no VEE required - making it a direct upgrade path for legacy designs where negative supply removal is desired.

What is the maximum operating frequency supported by SN65ELT21DGKR?

The SN65ELT21DGKR supports up to 200 MHz maximum switching frequency, verified under load conditions of RL = 500 Ω to GND and CL = 20 pF to GND. This is sufficient for PCIe Gen1 clock distribution, JTAG boundary-scan clocks, and industrial real-time control bus timing - with measured propagation delay of 2–4.5 ns and <20 ps RMS jitter ensuring timing margin integrity.