STMicroelectronics SM4T28AY

Overview

SM4T28AY from STMicroelectronics is an AEC-Q101-qualified unidirectional automotive TVS diode in SMA package, designed to clamp transient surges up to 38.9 V (V_CL) at 10.3 A (I_PP, 10/1000 µs), with 400 W peak pulse power and 0.2 µA leakage at 25 °C. It protects CAN, LIN, and sensor interfaces in 12 V automotive systems against ISO 7637-2 pulses (Pulse 1: −150 V; Pulse 2a: +112 V) and ISO 10605 ESD (±30 kV).

For engineers reviewing the SM4T28AY datasheet, SM4T28AY pinout, SM4T28AY application, or SM4T28AY equivalent, this device delivers verified clamping performance for battery-supplied ECUs, junction temperature resilience up to 150 °C, low dynamic resistance (0.446 Ω), and JEDEC-compliant SMA footprint compatibility with IPC-7531 layout standards.

Technical Context

The SM4T28AY employs planar silicon technology to achieve stable breakdown voltage (V_BR = 26.7–29.5 V at I_BR = 1 mA) and low leakage across −55 °C to +150 °C operating junction range. Its unidirectional configuration enables asymmetric surge suppression on positive-rail lines without reverse conduction path.

Clamping behavior follows V_CL = V_BR(max) + R_D × I_PP, where R_D = 0.446 Ω ensures predictable voltage limiting under 10/1000 µs transients. The device meets UL94 V0 resin flammability and supports reflow soldering per IPC/JEDEC J-STD-020 with peak profile ≤245 °C.

Key Specifications

Pinout & Package

SM4T28AY uses the industry-standard SMA (DO-214AC) surface-mount package per JEDEC outline, with 2.25–2.90 mm body width (D), 4.80–5.35 mm length (E), and 0.75–1.50 mm lead length (L). The package features UL94 V0 compliant epoxy resin and is optimized for FR4 PCBs with 70 µm copper thickness.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ28A and SMBJ28A, SM4T28AY offers lower V_CL (38.9 V vs. 45.4 V) and tighter V_BR tolerance (26.7–29.5 V vs. 31.1–34.4 V), making it optimal for next-generation automotive nodes where voltage headroom is constrained by 3.3 V or 5 V logic rails.

Availability

SM4T28AY is available at Aetrix Electronics and suitable for engine control units, CAN bus nodes, body control modules, and automotive lighting drivers requiring stable component supply across extended temperature ranges and rigorous automotive qualification.

Supply support for SM4T28AY 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 management solutions with vertical manufacturing and broad IP portfolio.

The SM4TxxAY series belongs to ST's automotive-grade TVS diode product line, engineered specifically for robust transient immunity in 12 V and 24 V vehicle electrical architectures per ISO 7637-2 and ISO 10605 standards.

FAQ

What is the maximum clamping voltage of SM4T28AY under a 10/1000 µs surge?

The maximum clamping voltage (V_CL) is 38.9 V at 10.3 A for a 10/1000 µs waveform, measured at T_amb = 25 °C. This value increases with junction temperature per α_T = 9.6 × 10⁻⁴/°C, reaching ~41.2 V at T_j = 125 °C using the V_CL temperature coefficient formula provided in DS6927.

Is SM4T28AY compatible with lead-free reflow soldering processes?

Yes - SM4T28AY supports lead-free reflow per IPC/JEDEC J-STD-020, with a recommended peak temperature of 240–245 °C for ≤60 seconds. The device's ECOPACK-compliant SMA package has been validated for thermal profiles with ramp rates ≤3 °C/s and cooling rates ≥−2 °C/s.

How does SM4T28AY differ from SM4T28CAY?

SM4T28AY is unidirectional (anode-to-cathode only conduction), while SM4T28CAY is bidirectional (symmetrical clamping for AC-coupled lines like LIN or differential buses). Their V_BR, V_CL, and R_D values are identical, but SM4T28CAY exhibits matched forward and reverse breakdown characteristics and higher junction capacitance.

Can SM4T28AY be used in 24 V commercial vehicle systems?

No - SM4T28AY is rated for V_RM = 24 V and is intended for 12 V nominal systems. For 24 V applications, ST recommends SM4T47AY (V_RM = 40 V) or SM4T56AY (V_RM = 48 V), which meet ISO 7637-2 Pulse 1 requirements down to −200 V and provide appropriate voltage margin above 28 V battery float voltage.