Automotive Circuit ProtectionThe automobiles being developed today are like mobile networks, interfacing a gamut of features/functions - embedded controls, mobile media and wireless options. The functioning of applications like infotainment, telematics, safety, and control need the utilization of many distinct networking standards (LIN, CAN, MOST, IDB-1394, Flex Ray, byte flight, Bluetooth for embedded control). Networking applications are linked through the wiring harness.
The embedded controllers, embedded/pluggable multimedia and wireless networked functions are operated either through the automobile battery or the ignition switch. The increasing range of critical automotive electronics could be affected by disturbances created by the electrical system, human interference and load dump pulses. Developing electronics for the automotive scenario is complex. Any change in temperature must be forecasted. Several applications can function in a temperature range of -40 to +85 °C. Under-hood applications would operate in severe conditions.
Electrostatic discharge can occur from various sources. Automobile users can lead to an increase in charge as they change positions internally. The process of plugging in a personal device to the automobile’s sound system can input ESD into the system. Dry air passing over an automobile can create ESD to build up on the radio inputs. Multi-Layer Varistor (MLV) devices are the most optimal ESD protection device. They have capacitance values in terms of hundreds of pF. Hence, they may not be relevant for high-speed data lines. Polymer ESD devices provide capacitance less than 1pF. The perfect low capacitance ESD devices operate an encapsulated air gap. The CG0402MLU series of devices (Bourns) is the most appropriate with a maximum capacitance (0.05pF). These technologies have large immediate “let through” voltages in excess of 100V during ESD events. Therefore, the use of silicon diode technology - Littelfuse SP3021 series can restrict the voltages. However, silicon technology devices can be expensive.
Load Dump Protection
Load dump power surges are distinct to automotive applications. Load dump pulses are temporary voltage spikes on the automobiles 12V power bus due to the gradual control of the alternator output voltage. The immediate eradication of a mega load on the power bus (such as a disconnected battery, a blown power fuse) will result in the alternator output to move to over 60 volts. In comparison to ESD pulses (measured in picoseconds), the long dump pulses are lengthy. The solutions for load dump may be metal oxide varistor (MOV) or transient voltage suppressor (TVS) diode devices.