This article provides a professional analysis of automotive load dump protection by a senior EMC protection expert from Leiditech (Shanghai Leimao Electronics). It focuses on the principles, industry standards, key component selection, and practical solutions for automotive load dump protection, offering a systematic approach to protection design for automotive electronics.

I. Unveiling Load Dump: The "Instant Killer" of Automotive Electronic Equipment

When the alternator is in a high-current charging state and the battery connection is suddenly interrupted (e.g., due to loose or corroded terminals), the magnetic field energy (E = ½LI², where L is the field inductance and I is the field current) stored in the alternator's internal field winding cannot be absorbed by the battery. This results in a destructive voltage spike on the power bus. This phenomenon is called load dump, which has three core high-level characteristics:

· High amplitude: The voltage instantly surges to tens or even hundreds of volts, far exceeding the normal operating range of 12V/24V automotive systems.

· High energy: The pulse duration ranges from 40ms to 400ms, and such long pulses can easily lead to the accumulation of significant thermal energy.

· High destructiveness: The energy is sufficient to cause permanent hard breakdown or thermal breakdown of downstream ECUs' components such as MCUs, transceivers, and logic chips.

II. Industry Standards: Core Comparison Between ISO 7637-2 (Old) and ISO 16750-2 (New)

The automotive electronics industry has now fully shifted toward the more stringent ISO 16750-2 standard, which is widely recognized as the "gold standard" for load dump protection. The key parameter comparisons between these two major standards are as follows:

Core conclusion: A solution that passes the 10 consecutive pulse tests required by the ISO 16750-2 standard has reliability that fully covers and exceeds the requirements of ISO 7637-2.

III. Protection Core: Operating Principle and Selection Criteria of TVS

Diodes

The TVS (Transient Voltage Suppression Diode) is the core component for handling load dump energy. Its protection process is divided into three stages, and engineers must focus on three key parameters when selecting the appropriate device.

(I) The "Three-Step" Working Logic of TVS Diodes

1. Standby Stage (High-Impedance State): When the circuit voltage is below VRWM (rated reverse stand-off voltage), the TVS remains in a silent state with only microampere-level leakage current, causing no interference with system operation.

2. Clamping Stage (Low-Impedance State): When the transient voltage exceeds VBR (breakdown voltage), the TVS quickly enters the avalanche breakdown region, its impedance drops sharply, diverting the surge current to ground and locking the residual voltage near the safe VC (clamping voltage).

3. Recovery Stage (Automatic Reset): After the load dump energy dissipates, the TVS automatically returns to the high-impedance state, allowing the circuit to continue operating without manual intervention.

(II) Three Essential "Benchmarks" for Engineer Component Selection

1. VRWM: Must be higher than the upper limit of the system's normal operating voltage to ensure the device does not trigger erroneously under normal conditions.

2. VBR: The threshold that distinguishes between the circuit's "normal operation" and "dangerous surge" states.

3. VC: The actual voltage that the downstream IC will withstand; it must be lower than the protected chip's absolute maximum rating voltage; otherwise, the protection will fail.

IV. Practical Guide: Precise Selection Method for Load Dump Protection Devices

Depending on whether the alternator has a built-in suppression circuit, a targeted protection strategy must be adopted. At the same time, common selection pitfalls should be avoided based on industry practices, and the current stress on the device should be estimated using formulas.

(I) Scenario-Based Protection Strategies

1. Strategy A (for Pulse 5a): The alternator has no suppression, resulting in the highest energy level. A high-power TVS (such as Leiditech's SM8S series) must be placed at the ECU input.

2. Strategy B (for Pulse 5b): The alternator has basic suppression, limiting the voltage to U_S. If this residual voltage is still higher than the MCU's withstand voltage, an additional TVS is required for "secondary clamping." In this case, the TVS's VRWM should be slightly higher than the suppressed U_S.

(II) Key Calculation Formula

Used to estimate the peak pulse current that the TVS will withstand, helping to determine the device's current stress:

IPP ≈ (US - VC) / Ri

Where:

· US = test voltage

· VC = TVS clamping voltage

· Ri = source impedance

(III) Industry Selection Practices and "Pitfall" Avoidance Guide

1. 12V systems: It is strongly recommended to select a TVS with a voltage rating greater than 24V. This accommodates scenarios such as jump starts or double battery voltage (24V) during vehicle maintenance. Selecting a device with too low a voltage rating (e.g., 14V) may cause the TVS to continuously conduct and burn out when 24V is forcibly applied.

2. 24V systems: A TVS rated at 33V or 36V is recommended.

(IV) The core of load dump testing is to simulate the high-energy transient overvoltage pulse generated when the battery and alternator (for fuel vehicles) or the output of the high-voltage to low-voltage DC-DC converter (for new energy vehicles) is accidentally disconnected. The core applicable principle is: all vehicle power ports that would be directly exposed to this transient pulse during a load dump event must undergo the corresponding test.

V. Advanced Protection: Series and Parallel Strategies of TVS Diodes

When a single TVS device cannot handle extreme energy levels or specific voltage requirements, series and/or parallel configurations can be used to enhance protection capability. The core value and potential risks of the two approaches are as follows:

VI. Leiditech Selection Recommendation: SM8S Series Automotive-Grade TVS Devices

Leiditech's SM8S series is a protection device specifically designed for automotive load dump protection. The entire series has passed AEC-Q101 automotive-grade certification and demonstrates excellent performance under the ISO 16750-2 standard. The key test results are as follows:

Key highlight: The SM8S24CA can continuously pass 10 consecutive tests under conditions of 0.5Ω low impedance and 400ms long pulses, demonstrating its thermal stability and chip consistency under extremely high current stress. This is a level of performance that many competing products — which claim to meet the standard but are only tested under 2Ω conditions — cannot achieve.

VII. Conclusion: A Systematic Engineering Approach to Automotive Load Dump Protection

Automotive load dump protection is not merely a matter of selecting a single component; it is a rigorous systematic engineering process. Practical verification through testing after theoretical calculations is a key step toward achieving mass production.

Leiditech, as a leading brand in EMC components and solutions, provides comprehensive support for automotive load dump protection:

1. Self-built professional EMC laboratory equipped with a complete load dump generator, offering free testing and rectification services to customers;

2. Fully adaptable solutions — from load dump protection to interface ESD protection — delivering one-stop customized reports;

3. All core devices are AEC-Q101 certified, ensuring high product reliability.

Take action now to put a "bulletproof vest" on your automotive electronic system! Please contact Leiditech to submit your circuit schematic for a free load dump analysis and device matching. See you at the Leiditech lab!