onsemi 1SMA18AT3G

Overview

1SMA18AT3G from ON Semiconductor is a unidirectional 400 W peak power Zener transient voltage suppressor (TVS) in SMA package, with 18 V working peak reverse voltage (VRWM), 29.2 V clamping voltage at 13.7 A peak pulse current, and <1 ns response time. It protects sensitive electronics in power supplies and industrial controls against ESD and lightning-induced surges.

For engineers reviewing the 1SMA18AT3G datasheet, pinout, applications, or equivalent options, key selection criteria include VRWM ≥ circuit operating voltage, clamping voltage margin relative to IC absolute maximum ratings, surge current capability under 10/1000 µs waveform, and thermal derating above 75°C ambient.

Technical Context

The 1SMA18AT3G operates as a unidirectional avalanche diode, triggered when reverse voltage exceeds its 20–22.1 V breakdown range at 1 mA test current. Its low zener impedance and fast <1 ns response enable effective suppression of ESD transients per IEC 61000-4-2 (Class 3, >16 kV HBM).

Designed for surface-mount use in the SURMETIC® SMA (Case 403D) package, it supports top-slide or bottom-board mounting with flat handling surface and cathode polarity band. Thermal resistance is 50 °C/W junction-to-lead and 250 °C/W junction-to-ambient on FR-4 board.

Key Specifications

Pinout & Package

SMA package (Case 403D, JEDEC DO-214AC), Pb-free, surface-mount, with cathode indicated by molded polarity band. Dimensions: 4.06–4.57 mm length × 2.29–2.92 mm width × 1.97–2.20 mm height.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar unidirectional TVS applications.

Compared with 1SMA18AT3G, SZ1SMA18AT3G adds automotive qualification without electrical trade-offs, while 1.5SMC18A trades compact size for higher surge capacity and thermal robustness-making each optimal for distinct mechanical and compliance constraints.

Availability

1SMA18AT3G is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, medical auxiliary rails, and telecom adapter outputs requiring stable component supply and full traceability.

Supply support for 1SMA18AT3G 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

ON Semiconductor is a global semiconductor manufacturer specializing in power management, analog, sensors, and discrete devices, with focus on energy-efficient and reliable solutions for automotive, industrial, and cloud infrastructure markets.

The 1SMAxxAT3G series belongs to ON Semiconductor's transient voltage suppressor product line, engineered for robust, cost-effective overvoltage protection in space-constrained surface-mount applications across harsh environments.

FAQ

What is the clamping voltage of the 1SMA18AT3G under standard surge conditions?

The 1SMA18AT3G has a maximum clamping voltage (VC) of 29.2 V when subjected to its rated peak pulse current of 13.7 A under the standard 10/1000 µs waveform. This value is measured at TJ = 25°C and defines the upper voltage limit imposed on protected circuitry during transient events. The 1SMA18AT3G maintains this clamping performance across its specified operating temperature range, making it suitable for use in environments where voltage margin to downstream ICs is critical.

Is the 1SMA18AT3G RoHS-compliant and lead-free?

Yes, the 1SMA18AT3G is a Pb-free device compliant with RoHS Directive 2011/65/EU and meets ON Semiconductor's lead-free manufacturing standards. The "T3G" suffix explicitly denotes Pb-free packaging, and the device uses void-free transfer-molded plastic with corrosion-resistant, readily solderable leads. Reflow profiles follow J-STD-020 guidelines, with maximum soldering temperature of 260°C for 10 seconds, as validated in the official ON Semiconductor packaging specification.

How does the 1SMA18AT3G differ from bidirectional TVS diodes like the 1SMA18CAT3G?

The 1SMA18AT3G is unidirectional and functions only during reverse-biased overvoltage events, behaving as a low-impedance path from cathode to anode when VRWM is exceeded. In contrast, the 1SMA18CAT3G is bidirectional and clamps in both polarities, making it suitable for AC lines or differential data buses. The 1SMA18AT3G offers lower capacitance (645 pF vs. ~700 pF for the C-series) and is preferred for DC power rails or single-ended signal lines where polarity is fixed and ESD robustness is prioritized.

What is the thermal resistance and power derating behavior of the 1SMA18AT3G?

The 1SMA18AT3G has a thermal resistance of 50 °C/W junction-to-lead (RJL) and 250 °C/W junction-to-ambient (RJA) on FR-4 board with minimum recommended footprint. Its DC power dissipation is 1.5 W at TL = 75°C, derating linearly at 20 mW/°C above that temperature; at TA = 25°C, PD is 0.5 W, derating at 4.0 mW/°C. These values are verified per ON Semiconductor's Case 403D layout guidelines and must be applied in thermal design to avoid junction overheating during sustained surge duty cycles.

Can the 1SMA18AT3G be used in place of a Zener diode for voltage regulation?

No, the 1SMA18AT3G is not intended for steady-state voltage regulation. It is optimized for transient suppression with high peak power (400 W) and fast response (<1 ns), but its zener impedance is not characterized for precision regulation, and its leakage current (2.5 µA max at VRWM) and tolerance (±5% on VBR) do not meet regulator-grade specifications. For DC voltage reference or regulation, dedicated Zener diodes such as the MMBZ5245B or TL431-based circuits should be used instead of the 1SMA18AT3G.