Texas Instruments SN65ELT21DR

Overview

SN65ELT21DR from Texas Instruments is a 5-V PECL-to-TTL level translator IC in SOIC-8 package, featuring 3 ns typical propagation delay, 24-mA TTL output drive, deterministic low-level output for open or sub-1.3-V inputs, and built-in temperature compensation. It enables reliable data/clock transmission over backplanes in telecom and industrial timing systems.

For engineers reviewing the SN65ELT21DR datasheet, SN65ELT21DR pinout, SN65ELT21DR application, or SN65ELT21DR equivalent, this page delivers verified electrical parameters, SOIC-8 terminal mapping, real-world use cases in backplane signaling and clock domain bridging, and validated alternative parts with documented functional and layout implications.

Technical Context

The SN65ELT21DR operates exclusively on a single +5-V supply (4.2 V to 5.7 V) with GND reference-no negative rail required. Its differential PECL input stage includes internal 50-kΩ pull-down resistors and a dedicated VBB reference output (3.62–3.74 V) for biasing ac-coupled inputs or terminating unused differential pairs.

It delivers TTL-compatible outputs with VOH ≥ 2.4 V (IOH = –3 mA) and VOL ≤ 0.5 V (IOL = 24 mA), supporting up to 200 MHz switching frequency. Random jitter is specified at 5–20 ps RMS, and propagation delay remains stable across –40°C to 85°C operating temperature range.

Key Specifications

Pinout & Package

SN65ELT21DR is housed in an industry-standard SOIC-8 package (D package), 3.9 mm × 4.9 mm body, 1.75 mm max height, with NiPdAu lead finish and MSL Level-1 rating. Pin 1 orientation follows Q1 quadrant in tape-and-reel packaging.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN65ELT21DR, MC100ELT21DG offers identical functionality with broader supply tolerance, while SN65LVDS21DR serves a different signaling standard entirely-requiring redesign of input termination and supply rails.

Availability

SN65ELT21DR is available at Aetrix Electronics and suitable for backplane interconnects, telecom clock distribution, industrial PLC I/O, and test equipment signal conditioning requiring stable component supply and long-term industrial lifecycle support.

Supply support for SN65ELT21DR 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, precision, and industrial-grade performance.

The SN65ELT21DR belongs to TI's high-speed interface translator product line, engineered specifically for robust PECL-to-TTL conversion in mission-critical timing and data transmission systems.

FAQ

What is the supply voltage range for SN65ELT21DR?

The SN65ELT21DR operates with VCC between 4.2 V and 5.7 V referenced to GND. It does not require a negative supply-VEE is not used. This single-supply operation simplifies power design compared to traditional ECL translators. The SN65ELT21DR maintains full AC and DC specifications across this entire range, including propagation delay and output drive capability.

How should the VBB pin be used in SN65ELT21DR applications?

The VBB pin on the SN65ELT21DR provides a stable 3.62–3.74 V reference output. When using single-ended PECL inputs, the unused D or D̅ input must be tied to VBB. For ac-coupled PECL inputs, VBB serves as the bias point. A 0.01 µF decoupling capacitor is required between VCC and VBB, and sink/source current must remain below ±0.5 mA to maintain accuracy. Leave VBB unconnected if unused.

Is SN65ELT21DR pin-compatible with MC10ELT21?

Yes, the SN65ELT21DR is explicitly documented as drop-in compatible with MC10ELT21 and MC100ELT21. All eight pins match in function and physical location in SOIC-8 package. No PCB changes are required when substituting SN65ELT21DR into existing MC10ELT21 layouts, provided VCC and thermal constraints align with the SN65ELT21DR's 4.2–5.7 V range and SOIC thermal characteristics.

What is the maximum operating frequency supported by SN65ELT21DR?

The SN65ELT21DR supports a maximum switching frequency of 200 MHz under standard load conditions (RL = 500 Ω to GND, CL = 20 pF). This specification is guaranteed across the full –40°C to +85°C temperature range and 4.2–5.7 V supply range. The device achieves this with 750–910 ps output rise/fall times and low jitter (5–20 ps RMS), making it suitable for OC-48 and STM-16 clock/data applications.

Does SN65ELT21DR require external pull-down resistors on its PECL inputs?

No, the SN65ELT21DR includes internal 50-kΩ pull-down resistors on its D and D̅ inputs. These ensure a deterministic low output (Q = LOW) when inputs are open or driven below 1.3 V-eliminating the need for external pull-down components. This feature enhances reliability in hot-swap, cable-disconnect, or unterminated scenarios without adding board area or BOM cost.