Kevin Parmenter, Director, Applications Engineering, Taiwan Semiconductor, NA
Protecting downstream automotive electronic system content vulnerable to “load dump” conditions is a major challenge in this market. Automotive systems require transient voltage suppressor (TVS) devices capable of shunting high-energy transients safely away from electronic circuits.
In addition to selecting TVS devices that can best handle load dump conditions, automotive systems designers must also comply with various industry standards – as well as the specifications many manufacturers demand for their own specific products.
This article explains the load dump condition that commonly occurs in vehicles, such as when the vehicle alternator is disconnected from the battery. It also describes a series of high-performance TVS devices. The wide selection of 52 devices can be tested and certified to meet industry standards and manufacturers’ specific requirements.
Protecting Against Load Dump
Overshoot and undershoot are not uncommon with any power electronics system. When a transient load is applied and removed, the response time to return to closed-loop control will depend on the feedback loop response of the system. The difference in an automotive system is that the amount of energy available during this recovery time can be extremely destructive if not clamped.
Vehicles, from cars to heavy construction equipment, are vulnerable to internally induced, excessively high energy transients. A “load dump” condition results when large loads are applied and removed, such as when a battery is repeatedly connected and disconnected from the alternator. When the battery is fully discharged, this transient overshoot voltage can reach over 100 volts and, with exceptionally low source impedance, the duration can last from 10s to 100s of milliseconds. These transients, if left undamped, can cause severe damage to the vehicle’s downstream electronic systems.
A load dump situation is not uncommon in a typical 12-volt automotive system. Corroded or loose battery cables, for example, can continually connect and disconnect due to vibration shock during driving. It can also be caused after jump starting. In this case, the jumper cables can connect-disconnect while the vehicle is running, causing overvoltage conditions to result from transient loading.
The most common fault conditions and resulting waveforms present in the automotive electrical system environment are shown in Figure 1. In addition to vehicles, OEM automotive electronic systems and aftermarket systems are subject to less-than-desirable electrical conditions. And transportation systems that use electrification, such as electric vehicles (EVs), can have similar use-case conditions that must be protected against.
Meeting Automotive Standards
Many automotive standards address how to test for the various fault conditions that automotive systems are subject to. Although well-intentioned, many of these specifications cannot meet the best estimates for energy levels and peak voltages of transients and surges. Electronic systems are becoming more and more sensitive as process geometries decrease and operating voltages are reduced. For this reason, transients and surges beyond the datasheet maximum operating specifications are more likely than ever to result in component or module failure.
There are numerous automotive-related specifications and test conditions for TVS device applications, often depending on the region, specific OEM and application use-case. Among the many modern automotive and transportation/equipment applications that need to adhere to protection specifications are marine, truck, bus, EVs/HEVs, aircraft, military, heavy-construction equipment, ATVs and others. The many industry specifications fall under EN, ISO and SAE automotive standards. Additionally, the many vehicle manufacturers who have created their own specifications include BMW, Chrysler, Nissan and Volvo, to name just a few.
Selecting TVS Devices
The load dump condition requires devices capable of safely dissipating this energy to prevent damage to downstream electronic systems. Designers need to choose protection devices that can meet a whole range of standard specifications and various automotive OEM requirements for a wide variety of applications for trucks and buses, heavy equipment, construction equipment, EVs, and many other transportation vehicles of various types and sizes.
The “closer in” the electrical system is to the battery, alternator, fuse block (wiring distribution systems), the higher the threat of the transient condition. The solution is to apply semiconductor TVS devices to conditions present in the vehicle systems. Transient voltage suppressor devices are essentially specialized Zener diodes optimized to clamp voltages. But unlike a typical Zener diode, which is used for regulation, TVS devices are designed to convert transient electrical energy to transient thermal energy, and are often used to assure that voltage overshoots do not exceed prescribed levels. Another key application of TVS devices are to protect against fast, high-voltage transients induced by lightning strikes and other external voltage disturbances in other types of electronic systems.
Figure 2 shows a typical TVS application in an automotive system. During a transient or surge event, the TVS device will clamp the voltage to a safe level that the rest of the electrical system can safely handle. It will also shunt the energy long enough to current-limit the source; or in some cases, it will clamp until an electronic circuit breaker or fuse can open, preventing further damage. Load dump TVS devices can withstand extremely high peak power (up to 6.6 KW), which makes them ideal for automotive load dump applications.
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Figure 2. TVS device protects against an automotive load dump condition
Benefits of Selecting TLD Series Devices
The TLD Series of TVS devices, by Taiwan Semiconductor, has been designed to protect onboard electronic devices from high-voltage surges emanating from the alternator when the battery becomes disconnected. In addition to being fully AEC-Q101 qualified, they meetISO7637-2 / ISO16750-2 surge specifications and IEC 61000-4-2 (Level: 4) / ISO 10605 (Level: L4) electrostatic discharge specifications. The devices in the series, with applicable standoff voltages, also meet Japan’s JASO A-1 (14V) and JASO D-1 (27V) load dump requirements.
The family of products in the TLD Series consists of 57 parts, offering designers a wide selection to choose from. Available in industry-standard DO-2018-AB packages, the devices are rated 3.6KW, 4.6KW and 6.6 KW and have a range of working standoff voltages (10 to 43V). To ensure performance during load dump conditions, they also have the industry-best clamping capability (17.0 to 69.4V). This offering of high-performance devices enable designers to cover the full range of automotive battery voltages they need to address.
Crucially for the designer, the TLD Series is available for testing to manufacturers’ specifications. Taiwan Semiconductor has invested in the necessary test equipment to be able to program the tester for simulation to each specification (Figure 3). When receiving requests from customers for testing to various specifications – and for all forms of transportation vehicles – the designer can work with the TVS supplier to find a device to meet the standard.
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Figure 3. Typical test showing pulse conditions present in an actual application use-case
Although most electronics systems need to be protected from transients and surges, automotive systems are particularly subject to fast, high-voltage transients from load dump conditions and external voltage disturbances. Not only do automotive designers need to protect vulnerable systems, they must also meet a confusing and stringent array of automotive standards and vehicle manufacturer specifications. High-performance TVS devices, such as the TLD Series, offer them the best choice for load dump applications. Working closely with the TVS device supplier, the designer can speed the component selection process for a wide range of automotive load dump applications.