onsemi MMT08B350T3G

Overview

MMT08B350T3G from onsemi is a bidirectional thyristor surge protective device (TSPD) designed for secondary overvoltage protection in telecom line interfaces. It features 350 V breakdown voltage, ±80 A peak surge current (10 × 1000 µs), 400–412 V breakover voltage at +65°C, and fails short-circuit under overstress-enabling robust protection of tip/ring lines in customer-premises telecom equipment.

For engineers reviewing the MMT08B350T3G datasheet, pinout, applications, or equivalent options, key selection criteria include bidirectional clamping behavior, holding current (130–270 mA), critical dv/dt rating (2000 V/s), low off-state leakage (<5 µA at V_DM), and SMB package compatibility with telecom PCB layouts requiring UL recognition (E210057) and Pb-free compliance.

Technical Context

The MMT08B350T3G operates as a crowbar-type protector: it remains high-impedance until transient voltage exceeds its breakover threshold (V_BO ≈ 400–412 V), then latches into low-impedance conduction until surge current falls below its holding current (I_H = 130–270 mA). Its bidirectional symmetry enables identical protection for both polarities without external polarity management.

It is rated for telecom-specific surge waveforms-including 10 × 1000 µs (±80 A), 10 × 560 µs (±100 A), and 8 × 20 µs (±250 A)-and meets Bellcore GR-1089, ITU-T K.20/K.21, IEC 60950, UL 1459/1950, and FCC Part 68 requirements when used in coordinated secondary protection circuits with PPTC or heat coils.

Key Specifications

Pinout & Package

MMT08B350T3G is housed in an SMB package (JEDEC DO-214AA), surface-mountable with no polarity marking. The device has two terminals: MT1 and MT2, electrically symmetrical and interchangeable for bidirectional protection.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SM15T350AY and P6SMB350A, the MMT08B350T3G delivers true bidirectional crowbar action with fail-safe shorting, enabling simpler, more robust secondary protection in telecom line interfaces where coordinated surge handling and guaranteed fault containment are mandatory.

Availability

MMT08B350T3G is available at Aetrix Electronics and suitable for DSL line interface protection, VoIP gateway tip/ring protection, ISDN U-interface protection, and central office terminal equipment requiring stable component supply and long-term lifecycle support.

Supply support for MMT08B350T3G 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 management, analog, sensor, and logic solutions for automotive, industrial, and communications markets.

The MMT08B350T3G belongs to onsemi's Thyristor Surge Protector (TSPD) product line, engineered specifically for secondary overvoltage protection in telecom infrastructure-balancing high surge capability, precise voltage thresholds, and fail-safe reliability in compact SMT packages.

FAQ

What is the primary function of the MMT08B350T3G in telecom protection circuits?

The MMT08B350T3G functions as a bidirectional crowbar-type surge protector that remains non-conductive until transient voltage exceeds its breakover threshold (~400–412 V), then latches into low-impedance conduction until current drops below its holding current (130–270 mA). This behavior makes the MMT08B350T3G ideal for secondary protection in telecom line interfaces where fail-safe short-circuit response is required to prevent latent failure.

Does the MMT08B350T3G require external bias or control circuitry to operate?

No, the MMT08B350T3G is a passive, self-triggering device with no external control pins or bias requirements. It relies solely on voltage and current thresholds-breakover occurs when applied voltage exceeds V_BO under specified dv/dt and current conditions, and turn-off occurs automatically when surge current falls below I_H. This autonomous operation simplifies integration and eliminates dependency on auxiliary power or timing circuits in the MMT08B350T3G design.

How does the MMT08B350T3G differ from standard TVS diodes like P6SMB350A?

Unlike unidirectional TVS diodes such as P6SMB350A-which clamp transient voltage but do not latch-the MMT08B350T3G provides crowbar action: once triggered, it sustains conduction until current decays below its holding current. This ensures continued shunting during the full surge event, reducing stress on downstream components. The MMT08B350T3G also fails short-circuit, whereas TVS diodes may degrade open-circuit after overstress.

Is the MMT08B350T3G compatible with Pb-free reflow soldering processes?

Yes, the MMT08B350T3G is explicitly marked as Pb-free and qualified for standard SMT reflow profiles. Its SMB package (DO-214AA) supports peak reflow temperatures up to 260°C for 10 seconds, aligning with IPC/JEDEC J-STD-020 moisture sensitivity and Pb-free process requirements. The MMT08B350T3G is listed in onsemi's Pb-free packaging documentation and carries the "G" suffix to denote RoHS compliance.

Can the MMT08B350T3G be used in DC power rail protection applications?

The MMT08B350T3G is not recommended for DC power rail protection due to its bidirectional crowbar behavior and lack of DC hold-off capability beyond its 350 V breakdown rating. In DC systems, sustained overvoltage could cause continuous conduction and thermal runaway unless current is externally limited below I_H. The MMT08B350T3G is optimized for transient AC-coupled telecom line protection-not steady-state DC bus clamping.