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One-shot ICs in an automotive environment

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Oct 12, 2009
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Hello, I am currently working on a small project that will use a dual one-shot IC (something like HCF4548B) and will be powered off a 12V automobile battery. I am not sure how I should power/connect the IC. Let me explain a little more about the project:

The HCF4548B has an absolute maximum rating for Vdd of up to 20V (I think), and it's trigger input is rated for Vdd+0.5V. I am planning to tap a momentary pushbutton switch for the one-shot triggers. When pressed, the switch connects 12V from the battery to the headlights. So basically what I want to do is take the battery (12v) side of the switch for the IC Vdd, and take the headlight side as the trigger input.

I am trying to design it so it will be protected from transient spikes, load dumps, and reverse battery connection. I know I could take an automotive regulator and use it for the IC Vdd, but I think (am not sure) that the delay when switching the regulator on would be too long to also use the regulator for the one-shot trigger. Consequently, since the one-shot trigger is rated for Vdd+0.5v, I can't use the regulator only for vdd and something else for the trigger.

Any ideas? Maybe I can get a dual automotive regulator (with enables). Connect both to the +12v side of the switch, one output to the IC vdd, the other to the IC trigger, and tie the other side of the pushbutton to the trigger regulator enable pin. Does that sound reasonable? How long should I expect the regulator to take to output after the enable pin is asserted?


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