Automotive-grade robustness
A device will plug into a vehicle's 12 V system. What do you do to make it survive?
| Level | ●● onsite technical |
| Track | Power |
| Really testing | Knowing the hostile environment. |
Going deeper
Extra explanation that is not in the book: worked numbers, where people go wrong, and how to say it in the room.
Name the standard and the numbers. For 12 V vehicles, ISO 16750-2 and ISO 7637-2 define the events. Typical figures to quote:
- Load dump: unsuppressed up to roughly 80–100 V for hundreds of ms; with central alternator clamping, about 35 V. Ask which test the customer's spec requires.
- Reverse battery: about −14 V for a minute.
- Jump start: about 24 V for a minute.
- Cold crank: down to about 4.5 V for tens of ms (some OEM profiles go lower).
Choosing the TVS. Its standoff voltage must sit above the jump-start voltage, or it will cook for a minute. Its clamping voltage at the test current must stay below the absolute maximum of everything behind it — which is why 40–60 V-rated regulators are common in this position.
Where people go wrong
- A series diode for reverse protection: 0.5–0.7 V lost and real heat at a few amps. An ideal-diode controller with a FET costs millivolts.
- Forgetting the cold-crank dip: the processor resets every time the engine starts.
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