onsemi NUP2105LT1G: CAN Bus ESD Protection and System Design Considerations

The robustness of a Controller Area Network (CAN) bus in harsh electrical environments is paramount for the reliability of modern automotive, industrial, and communication systems. A key component in safeguarding these networks is the NUP2105LT1G from onsemi, a bidirectional dual-line CAN bus protector designed to shield sensitive transceivers from Electrostatic Discharge (ESD) and other harmful transient voltage events.

This device integrates two series steering diodes and a Zener diode clamp in a single, compact SOT-23 package. Its primary function is to divert damaging transient currents away from the vulnerable CAN transceiver IC, thereby preventing latch-up and catastrophic failure. The NUP2105LT1G is engineered to meet stringent industry standards, offering robust ESD protection rated up to ±30 kV (IEC 61000-4-2, Air & Contact Discharge) and handling surge currents as defined by IEC 61000-4-5.

Critical System Design Considerations

While integrating the NUP2105LT1G is straightforward, its effectiveness depends on proper system design:

1. Placement and Layout: The protector must be placed as close as possible to the connector or the point of entry where ESD is likely to occur. This placement ensures transients are clamped before they can propagate into the printed circuit board (PCB) and reach the CAN transceiver. Keep the PCB traces between the connector and the protector short, direct, and wide to minimize parasitic inductance.

2. Grounding: A clean, low-impedance ground connection is vital. The ground pin of the NUP2105LT1G should be connected to the system ground plane with a short, low-inductance path to ensure fast and effective diversion of transient energy.

3. Matching the CAN Bus Common-Mode Choke: Many CAN designs include a common-mode choke (CMC) for electromagnetic compatibility (EMC). It is crucial to place the NUP2105LT1G on the line side of the common-mode choke (i.e., between the connector and the choke). Placing it after the choke on the transceiver side can cause reflected transients to damage the protection device or the transceiver itself, as the choke's impedance can prevent the transient from being properly clamped to ground.

4. Minimizing Loop Area: The loop area formed by the CANH, CANL, and ground traces should be kept as small as possible. A small loop area reduces parasitic inductance and minimizes the circuit's susceptibility to magnetic field coupling and radiated noise.

By addressing these design factors, engineers can create a hardened CAN interface. The NUP2105LT1G acts as a critical first line of defense, ensuring the network remains operational and data integrity is preserved when subjected to real-world ESD events and electrical fast transients (EFT).

ICGOO FIND: The onsemi NUP2105LT1G is an essential, space-efficient solution for achieving high-reliability CAN bus designs. Its superior bidirectional ESD protection capabilities, compliance with major immunity standards, and simple integration make it an optimal choice for protecting against transient threats in automotive and industrial applications.

Keywords: ESD Protection, CAN Bus, Bidirectional Diode, Transient Voltage Suppressor, System Hardening