STMicroelectronics SMBJ40A-TR

Overview

SMBJ40A-TR from STMicroelectronics is a unidirectional transient voltage suppression (TVS) diode designed for primary-level surge protection on DC power rails and signal lines. It features a 40 V stand-off voltage (VRM), 64.5 V clamping voltage at 9.7 A (10/1000 µs), 600 W peak pulse power rating, 0.2 µA max leakage at 25 °C, and SMB package with matte tin-plated leads - deployed in industrial power supplies and automotive body control modules.

For engineers reviewing the SMBJ40A-TR datasheet, SMBJ40A-TR pinout, SMBJ40A-TR application, or SMBJ40A-TR equivalent, key selection criteria include clamping voltage margin vs. protected IC V_DD, junction temperature derating above 25 °C, IEC 61000-4-2/4-4 compliance level, and thermal resistance under PCB copper area constraints.

Technical Context

This TVS diode operates as a voltage-clamped shunt protector: when transient voltage exceeds its breakdown threshold (44.4–46.7 V at 1 mA), it avalanches into low-impedance conduction to divert surge current away from downstream circuitry. Its planar silicon construction enables stable leakage performance up to 150 °C junction temperature and supports high-reliability SMPS and motor drive applications.

The device meets UL497B recognition (E136224) for isolated loop circuit protection and exceeds IEC 61000-4-2 Level 4 (±30 kV air/contact discharge) and IEC 61000-4-4 Level 4 (4 kV). Dynamic resistance is 1.59 Ω at 10/1000 µs, ensuring predictable clamping behavior across surge amplitudes.

Key Specifications

Pinout & Package

Package: SMB (DO-214AA), surface-mount, 2-terminal configuration with cathode band marking. Dimensions: 3.30–3.95 mm length × 5.10–5.60 mm width × 1.90–2.45 mm height (JEDEC registered outline).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ40CA-TR, SMBJ40A-TR provides lower leakage and simpler layout for DC rails; versus SMCJ40A, it trades peak power for compactness and faster response-critical in space-constrained 40 V power management designs.

Availability

SMBJ40A-TR is available at Aetrix Electronics and suitable for industrial power supplies, automotive body control modules, telecom remote power feeds, and renewable energy charge controllers requiring stable component supply across multi-year production cycles.

Supply support for SMBJ40A-TR 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, delivering intelligent power, sensing, and control solutions for automotive, industrial, and consumer markets.

The SMBJ series belongs to ST's transient protection portfolio, engineered specifically for high-reliability DC rail and interface protection where low leakage, precise clamping, and UL/IEC compliance are mandatory in harsh environments.

FAQ

What is the maximum allowable surge current for SMBJ40A-TR under IEC 61000-4-4 conditions?

The SMBJ40A-TR sustains 9.7 A peak pulse current (IPP) at 64.5 V clamping for 10/1000 µs waveform, and 48 A at 84 V for 8/20 µs. Its dynamic resistance of 1.59 Ω ensures predictable voltage rise per additional amp, enabling accurate system-level surge margin calculation.

Does SMBJ40A-TR require heatsinking in typical PCB layouts?

No dedicated heatsink is required. With R_th(j-a) ≈ 120 °C/W on standard FR4 (70 µm Cu, recommended footprint), and T_j(max) = 150 °C, the device safely handles 600 W pulses at 25 °C ambient. Thermal performance improves with ≥2 cm² copper area per lead, per Figure 12 in DS1283.

How does SMBJ40A-TR perform at elevated ambient temperatures?

At 85 °C ambient, leakage remains ≤1 µA, and clamping voltage increases linearly with junction temperature using α_T = 10.1 × 10⁻⁴/°C. Derated peak power drops to ~450 W at 100 °C T_j, per Figure 3 - design must account for this using actual board-level thermal modeling.

Can SMBJ40A-TR be used in place of SMBJ40CA-TR for bidirectional protection?

No - SMBJ40A-TR is unidirectional and conducts only in reverse avalanche; forward bias yields ~1.5 V drop (Figure 10), offering no clamping for negative transients. For true bidirectional protection, SMBJ40CA-TR or external series diode pairing is required.