STMicroelectronics SMA6T18AY

Overview

SMA6T18AY from STMicroelectronics is a unidirectional automotive-grade transient voltage suppressor (TVS) diode designed for ISO 7637-2 and ISO 10605 surge/ESD protection in 12 V/24 V vehicle power networks. It features a 18.0 V nominal breakdown voltage (V_BR), 25.2 V max clamping voltage (V_CL) at 24 A (10/1000 µs), 600 W peak pulse power, and 0.2 µA leakage at 25 °C - enabling robust protection of CAN, LIN, and sensor interface circuits in engine control units and body electronics.

For engineers reviewing the SMA6T18AY datasheet, SMA6T18AY pinout, SMA6T18AY application, or SMA6T18AY equivalent, this part supports high-reliability automotive designs requiring AEC-Q101 qualification, junction temperatures up to +150 °C, low-leakage planar construction, and compliance with IEC 61000-4-2 Level 4 (±30 kV contact/air), ISO 10605 (330 pF/330 Ω), and ISO 7637-2 Pulse 1/2a/3a/3b.

Technical Context

This TVS operates as a unidirectional clamping device in series with the protected line and ground, leveraging planar silicon technology to achieve stable V_BR temperature coefficient (α_T = 8.8 × 10⁻⁴/°C) and low dynamic resistance (R_D = 0.263 Ω at 10/1000 µs). Its response time is sub-nanosecond, ensuring suppression before downstream IC damage occurs during fast transients like load dump or ESD events.

The device is rated for bidirectional surge standards (e.g., ISO 10605) despite unidirectional polarity, due to its ability to clamp both positive surges (anode-to-cathode) and negative transients (cathode-to-anode reverse conduction under specified conditions), validated per IEC 61000-4-4 Level 4 (4 kV) and ISO 7637-2 Pulse 3b (+150 V).

Key Specifications

Pinout & Package

Package: SMA (JEDEC DO-214AC), surface-mount, matte tin-plated leads, MSL Level 1, footprint per IPC7531. Dimensions: 4.80–5.35 mm (E), 2.25–2.90 mm (D), 0.75–1.50 mm (L).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMA6T18A and SMBJ18A, SMA6T18AY delivers automotive-grade reliability in the smallest qualified footprint, with lower leakage and tighter V_BR tolerance - making it optimal for space-constrained, safety-critical vehicle networks where qualification and thermal performance are mandatory.

Availability

SMA6T18AY is available at Aetrix Electronics and suitable for engine control units, CAN/LIN bus nodes, automotive telematics modules, and body electronics requiring stable component supply across multi-year vehicle production cycles.

Supply support for SMA6T18AY 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, specializing in automotive, industrial, and power discrete technologies with vertical manufacturing and broad IP portfolio.

SMA6TY belongs to ST's Transil™ automotive TVS family, engineered specifically to meet stringent ISO 7637-2 and ISO 10605 requirements for 12 V/24 V vehicle electrical systems - prioritizing low leakage, high T_j, and AEC-Q101 compliance.

FAQ

What is the maximum clamping voltage of SMA6T18AY under a 10/1000 µs surge?

The maximum clamping voltage (V_CL) is 25.2 V at 24.0 A for a 10/1000 µs waveform, measured at T_amb = 25 °C. This value increases with junction temperature using α_T = 8.8 × 10⁻⁴/°C, reaching ~26.5 V at T_j = 125 °C - verified per DS6931 Rev 9 Table 2 and Figure 5.

Is SMA6T18AY bidirectional or unidirectional?

SMA6T18AY is unidirectional: it clamps positive transients on the cathode (K) relative to anode (A), and blocks reverse voltage up to −18.9 V (V_BR min). Its marking "6UHY" and ordering code "AY" (not "CAY") confirm unidirectional configuration per ST's ordering scheme in DS6931 Table 5.

Does SMA6T18AY require derating above 25 °C ambient?

Yes - peak pulse power must be derated linearly above 25 °C per Figure 3 in DS6931: at 85 °C, PPP drops to ~70% of 600 W (~420 W), and at 125 °C, it falls to ~45% (~270 W). Derating is based on junction temperature, not ambient, and depends on PCB copper area per Figure 12.

Can SMA6T18AY replace SMA6T18A in automotive production?

No - SMA6T18A lacks AEC-Q101 qualification and has not undergone automotive stress testing (HTOL, TCT, ESD). SMA6T18AY is the only version approved for OEM vehicle production; substituting SMA6T18A voids compliance and risks field failure under temperature cycling or vibration.