Automotive electronics designers are faced with many technical challenges during the system design process, foremost among those challenges is protecting buses and circuits from a variety of electrical hazards. Examples of these electrical hazards include: electrostatic discharge (ESD), switching spikes, starter crank, Load Dump, ignition coil interruption, and alternator field decay.
All of these pulses are included in the ISO7637-2 Standard, and are industry-defined transients. Overcoming these transient surges that have the ability to damage and disable the vehicle control units, infotainment electronics, sensors, injectors, valves and motors is one of the difficult challenges of the design process.
Communications between different components in vehicles have long relied upon a number of different buses to communicate information between systems, and Littelfuse has been the trusted supplier of transient voltage suppression (TVS) diodes and arrays to protect these systems for years. Among these buses are local interconnect network (LIN): a serial network protocol used for communication between components in vehicles and the control area network (CAN) bus: a vehicle standard designed to allow microcontrollers and devices to communicate with each other within a vehicle with no need for a host computer. Both are relatively low speed, 40 kbits/s and 1Mbit/s respectively. To enable multimedia capability and driver assistance cameras, a bus with greater speed was needed, which is where Ethernet (with some of the newest cars using 100Mbps Ethernet bus based upon the BroadR-Reach® platform), as well as the Universal Serial Bus (USB) data ports, which are used to provide “information” and “entertainment” (infotainment) to vehicle passengers, stepped in.
Ethernet advantages include reduced cabling costs, and they are better suited to the new high bandwidth requirements as mentioned above. Standards outlined in IEEE 802.1 and 802.3 define Ethernet technology and have enabled development of further standards and specifications (both physical layer and media access) that have allowed Ethernet protocols to evolve and to keep pace with the extensive demands of modern networks. Ethernet technology is well established and well understood outside of the automotive environment and it only makes sense to bring the technology to the automobile.
These new USB data ports, along with the adoption of Ethernet, are quickly accelerating in automotive electronic systems due to the rise in secure connected cars and the subsequent high demand for data transport. These buses have to be protected from the electrical environment of the automobile just as the older buses and ports needed protection from transient voltage spikes. Solutions will need to have characteristics including very fast response times and low RDYN values (leading to low clamp voltages), lower capacitance and low leakage current. Littelfuse transient voltage suppression (TVS) diodes and arrays are ideal solutions for protecting these new data ports and Ethernet buses from the various transient voltage threats enumerated above. TVS diodes and arrays can respond to over-voltage events faster than most other types of circuit protection devices and are offered in a variety of surface mount circuit board formats. Typically TVS devices are placed as close to the port connector as possible. When a transient event occurs, the TVS diode junction “avalanches”, providing a low impedance path to divert the transient current to ground without sustaining damage to the device and limits the voltage (often referred to as a “clamping” device) to a level that the circuit components and processors can survive. In addition to the need to protect against transient events, the signal integrity of the communication packet must be maintained, creating the need for these TVS devices to have a very low capacitance.
Littelfuse offers the broadest range of TVS diodes and arrays (that are AEC-Q101 qualified) on the market to help the automotive electronic system designers protect the circuits from transient events. As with earlier Littelfuse TVS protection diodes and array components, all of the offerings for the newer bus protection devices meet the industry quality standard for discrete semiconductors (AEC-Q101) and available to solve any transient problems. Specifically targeted for the newer Ethernet buses and USB data ports (Figure 1) in automobiles are the SP3012, SP3014, and SP3022 product lines.
Figure 1. Standard protection scheme for a USB 2.0 port
The low loading capacitance (sub 1pF) make them ideal for protecting high-speed signal lines such as USB2.0 and 1Gb Ethernet with an extremely low dynamic resistance (the SP3012 and SP3014 series offer the lowest dynamic resistance on the market producing the lowest clamping voltage for outstanding clamping performance) to protect the most sensitive, state of the art chipsets against ESD transients. Low leakage currents are also a plus and contact discharge ranges from +\- 12kV to +\- 20kV. Offerings come in a variety of industry standard surface mount devices (Figure 2) that enable efficient printed circuit board routing and placement.
Figure 2 Surface Mount Packages of TVS Components
When selecting TVS Diodes some important parameters to consider include reverse standoff voltage (VR), peak pulse current (IPP) and maximum clamping voltage (VC max). Example of the capabilities of Littelfuse TVS Diodes include low incremental surge resistance, the availability of unidirectional and bidirectional polarities, reverse standoff voltages ranging from 5 V to 495 V, and peak power ratings of 400 W to 30 KW. Consult the TVS diode selection guide , Automotive TVS Diode Application Note, and AEC-Q101 qualified TVS and Diode Arrays Selection Guide to learn more about how to select these devices and to view Littelfuse’s complete TVS diode offering in industry standard axial lead and surface mount packages. (Figure 3)
Figure 3 Automotive TVS Diodes in Industry Standard Packages
Littelfuse has long provided the automotive industry with trusted solutions to aid in the protection of sensitive automotive electronics in four main categories of vehicle systems: safety, performance and emissions, comfort and convenience and hybrid vehicles. Littelfuse backs its products with over 80 years of circuit protection expertise and application knowledge developed by collaborating and working with its industry-leading customers. Working with designers to provide transient voltage suppression (TVS) diodes and arrays with low clamping voltage, multiple package sizes and unlimited lifetime has solidified Littelfuse as the trusted provider of TVS products for many years to come.
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