Why needs overvoltage protection in Automotive ECU?
“Surge” means the voltage rise or fall abnormally in transient, especially in automotive. While the devices that need large power consumption, for example, automatic windows, motors switch on or power off, or switch on-off, circuit short etc. it will cause surge. The automotive electronic products are afraid to be damaged by surge, such as precise devices, audio or control computers. These devices are used lots of micro components inside, which are easy to be damaged by surge. Therefore, how to prevent these precise devices from damaging becomes an important issue.
ISO7637-2 Pulse 5a/5b
|Automotive Electronics System||Interface||SHA||MLA|
|System Power Supply||V|
How to Select Models
What are test criteria need to comply with?
- Is the circuit power less than or equal to working voltage of devices?
- Will the leakage current cause heat effect or other effects at normal working voltage?
- To calculate the maximum acceptable voltage of circuit.
- Test conditions of load dump.
Load Dump Circuit:
- C1 & C2: Electrostatic Capacitors. To consider capacitors fail and lead to short, the capacitance needs 1~47nF, rated voltage above 100V.
- R: Resistors, 0~22ohm. The main function is to share load dump. The resistance can’t be too large and needs to design base on actual current, due to I x R. The load dump energy of ISO7637 pulse 5 is absorbed by R and SHA mainly. It needs to do voltage test at low voltage. If R value is too large, the system is not sure to work at low voltage. If R value is too small, it’s not able to share load of SHA.
- SHA: the main device to clamp load dump.
- Diode: diodes.
- L4 & C3: for EMC purpose, to prevent current.
- C4: alike a battery between 100uF and 330uF, used in parallel. May add High Frequency filter behind capacitors in order to filter high frequency signal, for example Pulse 3a, 3b. Generally, the value is 1~47nF.
The automotive electronic products usually require the safety approval. Currently, it needs to pass test of ISO7637 pulse 5a. It also means “Load Dump Test”, which is a destroyed experiment. When the engine starts, the battery will be charged and cigarette plug will supply power 12V or 24V to electronic devices in car. Once the battery disconnected during driving, the engine will charge directly to these devices and will cause burned or damaged in safety. Therefore, all of famous automotive suppliers request the electronic devices must pass the safety requirements.