STMicroelectronics SMTPA68

Overview

SMTPA68 from STMicroelectronics is a bidirectional Trisil™ surge protection device in SMB (DO-214AA) package, designed for telecom line protection with 68 V standoff voltage, 93 V dynamic breakover voltage, and 50 A repetitive peak pulse current (10/1000 µs). It provides fail-safe short-circuit clamping for analog/digital xDSL and T1/E1 line cards.

For engineers reviewing the SMTPA68 datasheet, SMTPA68 pinout, SMTPA68 application, or SMTPA68 equivalent, this device is selected for GR-1089 Core Level 1 compliance, low 20 pF capacitance at 50 V, and UL497B/UL94 V0 certified reliability in telecom surge protection circuits.

Technical Context

SMTPA68 operates as a voltage-triggered crowbar device: it remains high-impedance below 68 V, then switches to low-impedance conduction above 93 V (dynamic VBO), sustaining conduction until current drops below 150 mA (IH min). Its bidirectional symmetry enables AC line protection without polarity constraints.

Thermal design relies on Rth(j-l) = 20 °C/W (junction-to-leads) and Rth(j-a) = 100 °C/W (junction-to-ambient with recommended footprint), supporting sustained surge handling under IEC61000-4-5 4 kV (10/700 µs) and FCC Part 68 Type A lightning surges (1500 V, 10/160 µs).

Key Specifications

Pinout & Package

SMB (DO-214AA) package: cathode-anode symmetrical bidirectional terminals; compact 5.10–5.60 mm × 4.05–4.60 mm body with 3.30–3.95 mm lead spacing; RoHS-compliant, ECOPACK® lead-free finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar telecom surge protection applications.

Compared with TPA68, SMTPA68 offers superior board-area efficiency and automated assembly compatibility; versus SMTPA100, it delivers lower clamping voltage for faster-acting protection on standard 48 V telecom lines, trading off slight capacitance increase for improved surge response timing.

Availability

SMTPA68 is available at Aetrix Electronics and suitable for DSL line cards, T1/E1 interfaces, ISDN terminals, and fax/modem analog port protection requiring stable component supply and long-term lifecycle support.

Supply support for SMTPA68 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, power, MCU, and protection devices for industrial, automotive, and communications markets.

SMTPA68 belongs to ST's Trisil™ family - purpose-built bidirectional surge protectors targeting GR-1089, ITU-T K-series, and FCC Part 68 compliance in telecom infrastructure and terminal equipment.

FAQ

What is the fail-safe behavior of SMTPA68 during surge events?

SMTPA68 enters a low-impedance short-circuit state when triggered, remaining latched until current falls below 150 mA. This fail-safe mode ensures downstream circuit disconnection via upstream fuse or breaker, eliminating risk of open-circuit failure or thermal runaway. Its UL497B listing confirms validated performance under repeated 50 A surges.

Can SMTPA68 be used in AC line protection without external components?

Yes - its intrinsic bidirectional symmetry allows direct placement across AC telecom lines (e.g., tip/ring) without series diodes or polarity-sensitive layout. The 68 V standoff and 93 V dynamic VBO ensure reliable blocking during normal operation and sub-100 ns triggering during transients, meeting ITU-T K20/K21 requirements without auxiliary circuitry.

How does SMTPA68's 20 pF capacitance impact xDSL signal integrity?

At 20 pF measured at 50 V bias and 1 MHz, SMTPA68 introduces negligible insertion loss (<0.1 dB) and phase distortion on ADSL2+ (up to 2.2 MHz) and VDSL2 (up to 30 MHz) signals. Its low capacitance preserves return loss >20 dB across band, enabling compliance with G.992.5 and G.993.2 spectral masks without equalization overhead.

Is SMTPA68 compliant with environmental and safety standards for telecom deployment?

Yes - SMTPA68 carries UL497B certification (E136224), UL94 V0 flammability rating, and ECOPACK® RoHS-compliant lead-free finish. It meets GR-1089 Core Level 1/2, IEC61000-4-5, FCC Part 68, and ITU-T K20/K21 surge immunity standards, making it qualified for use in central office, CPE, and network termination equipment worldwide.