onsemi 1SMB33CAT3G

Overview

1SMB33CAT3G from ON Semiconductor is a bidirectional transient voltage suppressor (TVS) diode designed for high-energy surge protection in DC power lines and signal interfaces. It features a 33 V working peak reverse voltage (VRWM), 40.6 V maximum clamping voltage at 11.3 A peak pulse current, and 600 W peak pulse power dissipation for 1 ms. Used in industrial power supplies and automotive ECUs to safeguard sensitive ICs against ESD and lightning-induced transients.

For engineers reviewing the 1SMB33CAT3G datasheet, pinout, applications, or equivalent options, key selection criteria include clamping voltage margin relative to protected circuit's absolute maximum rating, peak pulse current capability under IEC 61000-4-5 waveform, UL 497B certification for isolated loop protection, and Pb-free SMB package compatibility with automated SMT assembly.

Technical Context

The 1SMB33CAT3G operates as a bidirectional Zener-based TVS, leveraging avalanche breakdown to clamp both positive and negative transients symmetrically. Its low zener impedance (< 1 Ω typical) and sub-1 ns response time ensure rapid voltage limiting before downstream components experience overstress.

It is rated for 5.0 µA max reverse leakage at VRWM and exhibits 265 pF typical junction capacitance at 0 V bias, making it suitable for DC and low-frequency AC protection but not high-speed data lines. Thermal design must account for 226 °C/W junction-to-ambient resistance on standard FR-4 PCBs.

Key Specifications

Pinout & Package

Package: SMB (Case 403C), surface-mount, void-free thermosetting plastic housing with modified L-bend leads. Dimensions: 4.57 mm × 3.81 mm × 2.41 mm (L × W × H). RoHS-compliant, Pb-free, UL 497B recognized.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ33CA and 1.5SMC33CA, the 1SMB33CAT3G offers optimal balance of compact SMB footprint, UL 497B certification for isolated loops, and proven reliability in industrial temperature ranges (−65 °C to +150 °C), making it preferred for space-constrained, safety-certified designs.

Availability

1SMB33CAT3G is available at Aetrix Electronics and suitable for industrial power supplies, automotive ECUs, medical equipment power inputs, and programmable logic controllers requiring stable component supply and long-term lifecycle support.

Supply support for 1SMB33CAT3G 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 for automotive, industrial, and cloud power applications.

The 1SMB33CAT3G belongs to the 1SMBxxCAT3 series of bidirectional TVS diodes engineered specifically for robust, cost-effective surge protection in harsh environments-emphasizing high peak power, fast response, and safety certifications like UL 497B.

FAQ

What is the clamping voltage of the 1SMB33CAT3G and how is it measured?

The 1SMB33CAT3G has a maximum clamping voltage (VC) of 53.3 V at 11.3 A peak pulse current (IPP), tested with a 10/1000 µs waveform per IEC 61000-4-5. This value is measured across the device terminals during surge conduction and represents the highest voltage seen by downstream circuitry. The 1SMB33CAT3G maintains this clamping performance consistently across its qualified temperature range (−65 °C to +150 °C).

Is the 1SMB33CAT3G suitable for protecting CAN bus power lines?

Yes, the 1SMB33CAT3G is widely used for CAN bus power line protection in automotive and industrial applications. Its 33 V VRWM aligns with 24 V nominal systems, and its 53.3 V clamping voltage stays safely below the 58 V absolute maximum rating of common CAN transceivers. The 1SMB33CAT3G's UL 497B recognition further validates its suitability for isolated communication interfaces.

Does the 1SMB33CAT3G have polarity markings on the package?

No, the 1SMB33CAT3G is a bidirectional TVS diode and does not require polarity marking. The datasheet explicitly states "Polarity band will not be indicated" for this series. Either terminal may be connected to the protected line or ground-the device clamps symmetrically for both positive and negative transients.

What is the junction capacitance of the 1SMB33CAT3G and how does it affect circuit design?

The 1SMB33CAT3G exhibits 265 pF typical junction capacitance at 0 V bias and 1 MHz. This value is low enough for DC power rails and low-frequency analog signals (e.g., sensor excitation, 4–20 mA loops) but unsuitable for high-speed data lines such as USB 2.0 or Ethernet. Designers must verify that 265 pF does not degrade signal rise/fall times or cause timing skew in the target application.

How does the 1SMB33CAT3G differ from unidirectional TVS diodes like 1SMB33AT3G?

The 1SMB33CAT3G is bidirectional and protects against transients of either polarity, while the unidirectional 1SMB33AT3G only clamps positive surges (anode grounded). The "C" suffix denotes bidirectional construction. For AC-coupled or floating DC circuits-such as RS-485 buses or transformer-isolated supplies-the 1SMB33CAT3G eliminates the need for dual-diode configurations, simplifying layout and reducing BOM count.