Power supply / logic in automotive

[Morcego]

Hi,

I have to design a microcontroler circuit to operate inside a car (in these case a BUS). Do I have to be extra carefull in designing the power supply (5v) and protect the logic? I have seen some automotive designs with a lot of ferrites. Is really necessary or a standard approach is good enough ? )Using only large local electrolitic capacitors).

Thanks in advance.

Joaquim

 

[VEBill]

Yes.

Search on alternator 'load dump' as a starting point.

 

[Morcego]

Thanks VE1BLL

Linear Technology as a switching regulator, the LM1977 that as load dump protection, reverse voltage and is specially design to automotive applications. Do you think it will do the job? I want to keep the design as simple as possible.

Thanks in advance.

 

[Warpspeed]

An automotive electrical system is about the most electrically hostile environment imaginable. Lots of relays in the system switching up to tens of amps creating fast inductive spikes and ringing well up into radio frequencies. Very high energy alternator load dumps. Then half asleep "Fred" with his hardware store jumper leads applying minus 12V to start the car on those cold mornings.

Then there are people that like to use electric welders to do car repairs. Pretty frightening stuff....

High speed digital circuitry absolutely must have a clean ground and supply, and all the inputs/outputs need to be noise free too. The RF tight enclosure with all those high frequency bypass capacitors and ferrites are definitely required.

Another defensive feature is robust software that can recover if the program does crash. Invalid opcode traps and watchdog timers are useful. Any large areas of unused memory should be filled with "no ops" and a jump to program start placed at the very end. An imaginative programmer should know lots of little tricks. But the hardware should be the first line of defense.

 

[InstruEngineer]

Hi
In case of Automotive circuits, the selection of components depends on the place of Installation
Like If the unit is to be kept in engine room then normal operating temperature range is -40C to +125C but if it is gona be kept in passenger compartment then range can be -40c to +65C or +85C
then there will be many others specs like surge ratings (you can refer different standards of automobile companies if your customer doesnot have one), emc/emi specification (thats y u will see ferrites in power supply ckt), alternator dump, load dump and many more
Normally if you design a circuit it will work fine logically in normal environment but when you consider all the above specifications your ckt may not work
so from start you shld consider all the specs to design the ckt




Instruite
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[IRstuff]

If your part is designed for automotive applications, then there should be an app note that describes the recommended connections and configurations.

TTFN