Protection against automotive power supply hazards

I'm looking for a way to protect a small circuit which is to be used inside of a car or truck (12V or 24V power system). The circuit consumes about 12-15W. I use an isolated DC/DC converter module which can regulate 9-36V down to 3.3V.

I'm looking for recommended circuits or a controller IC that can take care of the usual hazards:

1. Load Dump Spikes


2. Reverse Voltage


3. OV/UV Protection


4. General noise on the power lines.



5. ... Anything I might have missed.

Currently I have my eye on the LTC4365 from Linear Technologies. I've thought about using it together with a bi-directional TVS, clamping the voltage to 32V and protecting everything with a fast blowing fuse.

Would this be a proper solution or did I miss something here?

Answer

Load-dump

... is a killer - your TVS has to turn a huge amount of energy into heat without going pop.

ISO7637 for a 12V system has a spike peaking at up to ~90V with a rise time of 5-10ms lasting up to 400ms from a source resistance as low as 0.5ohms. That's several hundred Joules of energy in less than half a second!

Not all of that has to go into the suppressor - only the excess above the clamping voltage (but still ~60V in your case)

On the bright side, load-dumps are pretty rare, so if it's a one-off and you don't mind the small risk, you could ignore it.

Fast transient spikes

These can reach 200V when the wipers switch off for example - provide a (high-voltage-rated) capacitive route for those to ground right near the input.

Longish-term over-voltage

Automotive electronics is often specified to survive 24V for several minutes (for when a car is jump-started off a 24V truck) and 48V for up to a minute (IIRC) as sometimes 2 truck batteries are used to provide a quick boost charge to get a car moving in extremis! Your spike suppressor may pop under those conditions.

Dropouts

Battery dropouts can also be significant, there's a test in the industry which involves a series of pulses battery voltage falling to 0V - you need to have enough internal capacitance to keep your supply rails up when that happens.

Real-world requirements specification

If you want an example of how gory this can get, Ford's electromagnetic compatibility (EMC), which includes transient testing, is available on the web:

Component EMC Specifications EMC-CS-2009

Search through it for "transient" and "dropout" to see what series-production designs are supposed to live up to!