[Efi332] HW Question (for JC)

[Paul Helmuth]

Jeff,

I managed to source a couple of National LM2940T (9volt output) regulators. I am hoping to use this part to power my Phytec development board from the car's 12v battery.

The "Typical Application" section of the data sheet shows only two external components. 

One is a .47 microfarad capacitor on V-in to ground. An asterisk note indicates that this is required if the regulator is located far from the "power supply filter". Which seems to imply that there should be some filtering in place between the battery and the regulator (though there is no diagram of what such a filter should look like).

The second external component is a 22 microfarad (minimum) capacitor on V-out to ground. The interesting note on the output capacitor is that the equivalent series resistance is critical. Reading the performance characteristics table relating to the output capacitor ESR, I see that I need to use a capacitor with an ESR between .1 and 1 ohm. I have never seen ESR given for capacitors. Can you give me any pointers as to how I can determine and arrive at an acceptable ESR for the output capacitor(s)?

Thanks,
-Paul
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