onsemi MMT08B260T3G

Overview

MMT08B260T3G from onsemi is a bidirectional thyristor surge protective device (TSPD) designed for secondary overvoltage protection in telecom line interfaces. It features 260 V breakdown voltage, ±80 A 10×1000 µs surge current rating, 150–300 mA holding current, and fails short-circuit under overstress-enabling robust lightning and cross-talk transient suppression in customer-premises equipment.

For engineers reviewing the MMT08B260T3G datasheet, pinout, applications, or equivalent options, key selection criteria include bidirectional breakover behavior, dv/dt immunity (≥2000 V/s), low capacitance (<55 pF), UL E210057 registration, and Pb-free SMB package compatibility with telecom regulatory standards (ITU K.20/K.21, Bellcore 1089).

Technical Context

The MMT08B260T3G operates as a crowbar-type protector: it remains high-impedance below 260 V, triggers at 320–340 V (±65°C), and latches on until surge current falls below its 150–300 mA holding threshold. Its bidirectional symmetry ensures identical forward/reverse protection without polarity dependence.

It delivers 2000 W instantaneous peak power (10×1000 µs, 50 A), withstands ±300 A/µs di/dt, and maintains stable voltage limiting across transient amplitudes and slew rates-critical for maintaining signal integrity during multi-pulse surge events in analog telecom lines.

Key Specifications

Pinout & Package

MMT08B260T3G is housed in an SMB package (JEDEC DO-214AA, Case 403C), surface-mountable with gull-wing leads. The device is polarity-insensitive and has two terminals: MT1 and MT2, electrically symmetric for bidirectional operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SM260A and PSM712, the MMT08B260T3G uniquely combines SMT SMB packaging, bidirectional 80 A surge capability, and intrinsic fail-short behavior-making it the only option qualified for primary secondary protection in regulated telecom CPE designs requiring UL/ITU compliance.

Availability

MMT08B260T3G is available at Aetrix Electronics and suitable for DSL line interface protection, voice band analog loop protection, and ISDN BRI protection requiring stable component supply, full traceability, and long-term lifecycle support.

Supply support for MMT08B260T3G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and logic solutions for automotive, industrial, cloud, and communications markets.

The MMT08B260T3G belongs to onsemi's Thyristor Surge Protector (TSPD) product line, engineered specifically for secondary overvoltage protection in telecom infrastructure and customer-premises equipment meeting stringent international safety and surge immunity standards.

FAQ

What is the function of the MMT08B260T3G in a telecom line circuit?

The MMT08B260T3G functions as a bidirectional crowbar-type surge protector that remains non-conductive below 260 V, triggers at 320–340 V during overvoltage events, and latches on until current drops below its 150–300 mA holding threshold. In telecom line circuits, it shunts lightning- and induction-induced surges away from sensitive codecs and transformers, ensuring system reliability per ITU K.20/K.21 and Bellcore 1089. The MMT08B260T3G is designed for this exact role in TIP/RING protection networks.

Does the MMT08B260T3G have polarity markings or directional installation requirements?

No, the MMT08B260T3G is a fully bidirectional device with no polarity markings or directional installation requirements. Its MT1 and MT2 terminals are electrically symmetric, and it provides identical breakover and conduction characteristics in both forward and reverse polarities. This eliminates orientation errors during SMT placement and simplifies layout in differential telecom line pairs. The MMT08B260T3G data sheet explicitly confirms bidirectional operation across all electrical parameters.

What does "fail-safe shorts when overstressed" mean for the MMT08B260T3G?

"Fail-safe shorts when overstressed" means that upon catastrophic overvoltage or excessive surge energy beyond its ratings, the MMT08B260T3G permanently transitions to a low-resistance short-circuit state rather than opening or degrading silently. This ensures downstream circuitry remains protected-even after end-of-life-and provides a clear fault indication (e.g., blown fuse or tripped breaker). The MMT08B260T3G implements this behavior by design, distinguishing it from non-semiconductor protectors subject to wearout.

How does the MMT08B260T3G meet UL 1459 and FCC Part 68 requirements?

The MMT08B260T3G meets UL 1459 and FCC Part 68 requirements through its UL E210057 registration, verified 200 V off-state voltage margin, controlled 1.53–3.0 V on-state voltage during clamping, and validated performance under Bellcore 1089 and ITU K.20/K.21 surge waveforms. Its fail-safe short-circuit failure mode and Pb-free SMB package further satisfy construction and safety clauses in these standards. The MMT08B260T3G is explicitly cited in onsemi's compliance documentation for telecom CPE applications.

Can the MMT08B260T3G be used without a series current-limiting resistor?

No, the MMT08B260T3G must be used with a series current-limiting resistor or PPTC device to ensure surge current remains within its 150–300 mA holding current range during clamping. Without external impedance, sustained line voltage could maintain conduction indefinitely, leading to thermal runaway. Typical designs pair the MMT08B260T3G with a 10–100 Ω resistor or polymeric PTC upstream-this coordination is documented in onsemi's telecom protection reference schematics for the MMT08B260T3G.