Vishay General Semiconductor - Diodes Division SM6T18CA-M3/5B

Overview

SM6T18CA-M3/5B from Vishay General Semiconductor is a bidirectional transient voltage suppressor (TVS) diode in SMB (DO-214AA) package, designed for clamping voltage transients on signal and power lines. It features 18 V standoff voltage (VWM), 25.2 V maximum clamping voltage at 24 A peak pulse current (10/1000 μs), 600 W peak pulse power rating, and operates from –65 °C to +150 °C. It is widely used for ESD and surge protection in automotive sensor interfaces.

For engineers reviewing the SM6T18CA-M3/5B datasheet, SM6T18CA-M3/5B pinout, SM6T18CA-M3/5B application, or SM6T18CA-M3/5B equivalent, key selection criteria include bidirectional clamping capability, low clamping ratio (25.2 V / 18 V = 1.4), halogen-free RoHS compliance (M3 suffix), AEC-Q101 qualification readiness, and compatibility with automated SMT placement on standard PCB pad layouts.

Technical Context

The SM6T18CA-M3/5B implements a silicon avalanche junction structure optimized for fast response (<1 ns) to transient overvoltages. Its bidirectional symmetry enables protection of AC-coupled or differential signal paths without polarity constraints.

It delivers 600 W peak pulse power handling per the 10/1000 μs waveform standard, with thermal resistance R_θJA = 100 °C/W and R_θJL = 20 °C/W, enabling reliable operation under repetitive surge conditions when mounted on minimum recommended 5.0 mm × 5.0 mm copper pads.

Key Specifications

Pinout & Package

SM6T18CA-M3/5B is housed in an SMB (DO-214AA) package with two terminals: anode and cathode. As a bidirectional device, it has no polarity marking and functions identically in either orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar transient voltage suppression applications.

Compared with SMAJ18CA and 1.5KE18CA, the SM6T18CA-M3/5B provides optimal balance of 600 W surge handling, SMB footprint density, low 1 μA leakage at 18 V, and MSL Level 1 reflow compatibility-making it preferred for modern automotive and industrial SMT platforms where space, reliability, and process compatibility are jointly constrained.

Availability

SM6T18CA-M3/5B is available at Aetrix Electronics and suitable for automotive sensor interfaces, industrial CAN bus nodes, consumer USB port protection, and telecom DSL line interfaces requiring stable component supply and halogen-free compliance.

Supply support for SM6T18CA-M3/5B 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

Vishay General Semiconductor is a global leader in discrete semiconductors, specializing in diodes, rectifiers, MOSFETs, and protection devices with emphasis on reliability, efficiency, and application-specific optimization.

The SM6T Series is engineered for high-reliability transient suppression in harsh environments, targeting automotive, industrial, and telecom applications where robustness against ESD, lightning, and inductive switching surges is mission-critical.

FAQ

What is the clamping voltage of SM6T18CA-M3/5B at its rated peak pulse current?

The SM6T18CA-M3/5B has a maximum clamping voltage (V_C) of 25.2 V when subjected to a 10/1000 μs waveform peak pulse current (I_PPM) of 24 A. This value is measured under standardized test conditions per JEDEC and IEC 61000-4-5, and reflects the actual voltage seen by protected circuitry during worst-case surge events. The SM6T18CA-M3/5B maintains this clamping performance across its full operating temperature range.

Is SM6T18CA-M3/5B suitable for automotive applications?

Yes, SM6T18CA-M3/5B is qualified for automotive use via the HM3 suffix variant (e.g., SM6T18CAHM3_B/I), which carries AEC-Q101 certification. While the base SM6T18CA-M3/5B is commercial-grade, its construction-including glass-passivated junction, MSL Level 1 rating, and –65 °C to +150 °C operating range-supports automotive deployment. Designers should specify the HM3 suffix version for production automotive programs requiring formal qualification evidence.

How does the "CA" suffix in SM6T18CA-M3/5B indicate device functionality?

The "CA" suffix in SM6T18CA-M3/5B explicitly denotes a bidirectional configuration, meaning the device provides symmetrical transient suppression for both polarities without requiring orientation during placement. Unlike unidirectional "A"-suffix parts, the CA variant has no cathode band marking and exhibits identical V_BR, V_C, and leakage characteristics in either direction-enabling simplified design for AC-coupled or differential signal lines. The SM6T18CA-M3/5B leverages this symmetry for robust protection in CAN, USB, and telecom interfaces.

What is the thermal resistance of SM6T18CA-M3/5B, and how does it affect PCB layout?

The SM6T18CA-M3/5B has a typical junction-to-ambient thermal resistance (R_θJA) of 100 °C/W when mounted on 0.2" × 0.2" (5.0 mm × 5.0 mm) copper pads per terminal. This value assumes minimal copper area; increasing pad size or adding internal ground planes reduces R_θJA and improves surge endurance. For repeated transient events, designers must ensure adequate copper area and avoid thermal bottlenecks near the SM6T18CA-M3/5B to prevent junction temperature exceeding 150 °C.

Does SM6T18CA-M3/5B require derating at elevated ambient temperatures?

Yes, SM6T18CA-M3/5B requires derating above 25 °C ambient temperature, as shown in Figure 2 of the Vishay datasheet (Doc. #88385). Its peak pulse power capability decreases linearly: at 85 °C ambient, PPPM drops to ~70 % of the 600 W rating at 25 °C. This derating applies to both single-pulse and repetitive surge conditions. Designers must verify worst-case ambient + self-heating stays within the SM6T18CA-M3/5B's 150 °C maximum junction temperature limit using the specified R_θJA and expected pulse duty cycle.