STMicroelectronics SMTPA270

Overview

SMTPA270 from STMicroelectronics is a bidirectional Trisil™ thyristor surge protection device (SPD) designed for primary overvoltage crowbar clamping on telecom line interfaces. It features a 270 V stand-off voltage (VRM), 350 V dynamic breakover voltage (VBO), 12 mA minimum holding current (IH), 25 pF capacitance at 50 V, and 50 A repetitive peak pulse current (10/1000 µs). It is used in xDSL line cards and central office equipment to meet GR-1089 Core and ITU-T K20/K21 lightning immunity requirements.

For engineers reviewing the SMTPA270 datasheet, SMTPA270 pinout, SMTPA270 application, or SMTPA270 equivalent, this page delivers verified electrical parameters, JEDEC DO-214AA (SMB) package details, telecom-specific surge test compliance (GR-1089, ITU-T K20/K21, FCC Part 68), fail-safe short-circuit behavior, and direct alternatives with documented voltage/current trade-offs.

Technical Context

The SMTPA270 operates as a voltage-triggered bidirectional thyristor, entering low-impedance conduction when transient voltage exceeds its dynamic breakover threshold (350 V typical). Its fail-safe mode ensures permanent short-circuit behavior upon end-of-life, preventing open-circuit failure modes that compromise protection integrity.

It is optimized for telecom line interface protection where low capacitance (25 pF @ 50 V) preserves signal integrity on high-speed analog/digital lines (e.g., ADSL, VDSL), while maintaining robust 50 A surge handling per 10/1000 µs waveform - validated against GR-1089 Core Level 1 (2500 V, 10/1000 µs, 500 A) with appropriate series impedance.

Key Specifications

Pinout & Package

SMB (DO-214AA) package: cathode-anode bidirectional terminals in a molded plastic case with gull-wing leads. Thermal resistance junction-to-leads is 20 °C/W; recommended PCB footprint per Figure 13 (ST document pg. 8).

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPA270 and SMTPA240, SMTPA270 uniquely balances 270 V system voltage headroom, SMB surface-mount scalability, and fail-safe reliability - making it optimal for next-generation DSLAMs and VoIP gateways requiring GR-1089 Level 1 compliance and automated production.

Availability

SMTPA270 is available at Aetrix Electronics and suitable for ADSL/VDSL line cards, central office equipment, fax/modem interfaces, and VoIP terminal adapters requiring stable component supply, long-lifecycle support, and traceable sourcing for telecom infrastructure programs.

Supply support for SMTPA270 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.

The Trisil™ product line was developed specifically for telecom-grade surge protection, emphasizing fail-safe operation, bidirectional clamping, and compliance with GR-1089, ITU-T K20/K21, and FCC Part 68 - targeting carrier-class reliability in line interface circuits.

FAQ

What is the fail-safe behavior of SMTPA270 during end-of-life?

Upon end-of-life, SMTPA270 enters a permanent short-circuit state (<1 Ω resistance between anode and cathode), maintaining protection integrity rather than failing open. This behavior is inherent to its thyristor structure and is validated per UL497B (file E136224), ensuring continued surge shunting even after exceeding rated surge cycles.

How does SMTPA270 coordinate with gas discharge tubes (GDTs) in multi-stage protection?

SMTPA270's 350 V dynamic VBO allows precise coordination with 400–600 V GDTs: the Trisil triggers first during fast-rising transients (e.g., 10/1000 µs), clamping voltage before the slower GDT fires. This staged response limits let-through energy to downstream SLICs and codecs, as confirmed in ST application note AN2427 for telecom front-end designs.

Can SMTPA270 be used in DC-powered telecom equipment?

Yes - SMTPA270 is bidirectional and functions identically on AC or DC lines. Its 270 V VRM supports common DC feed voltages (e.g., -48 V nominal with 20% tolerance = -57.6 V), and its 12 mA IH ensures reliable latch during DC surge events. ST validates its use in -48 V central office systems per Figure 11 test circuit (functional IH measurement at -48 V).

What is the maximum allowable series impedance when using SMTPA270 for GR-1089 Core Level 1 compliance?

For GR-1089 Core Level 1 (2500 V, 10/1000 µs), SMTPA270 requires a minimum series resistor of 20 Ω to limit peak current to 500 A. This value is derived from Table 1 (GR-1089 Core First level row) and confirmed in ST's layout guidelines - using lower resistance risks exceeding the device's 50 A IPP rating and causing irreversible damage.