Power Supply for Automotive Applications based on HC08 GP32 uC

[GCataldo]

Hi,

Do someone know some information with respect to design considerations in power supply for automotive application using microcontrolers?

ie. Power line filter estrategies, Isolations....

Thanks in advance.

Giancarlos Cataldo

gcataldo@usb.ve

Universidad Simón Bolivar

Caracas, Venezuela.

[glork]

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GCataldo wrote:

Hi,

Do someone know some information with respect to design considerations in power supply for automotive application using microcontrolers?

ie. Power line filter estrategies, Isolations....

Thanks in advance.

Giancarlos Cataldo

gcataldo@usb.ve

Universidad Simón Bolivar

Caracas, Venezuela.

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HI GCataldo.
I can offer a rough guide-line, as follows:
1. The first component in the + supply line should be a diode with the anode toward +Vbatt and the cathode toward your device.
2. Next should come a noise filter consisting of at least this: a series choke followed by a capacitor to ground followed by another series choke (higher freq) followed by another cap to ground. This is a common "pi" filter. You will have to work out component values, but the first choke might be 100uH, the first cap approx. 1uF, the second choke 10uH and the second cap 0.1uF.
3. Finally you will need a voltage regulator. Which ever one you choose you must remember to use the automotive rated part. This is because transients of up to approx. 60 Volts can occur in automotive power wiring. Standard 3-terminal regulators wont withstand that.
Hope this helps.
ron

[GCataldo]

glork.

Thanks a lot.

I am thinking something like that.

My device consumption is about 1.5A @ 5V

Basically as you comment:

Step 1. Inverse Polarity Protection.

Step 2. Line Filter. Does this PI Filter support my consumption needs?

Step 3. What do you thing about DC-DC acopling? Is a good idea to use a switching power supply in Microcontroler based devices?

Giancarlos Cataldo

gcataldo@usb.ve

Universidad Simón Bolivar

Caracas, Venezuela.

[rhinoceroshead]

Glork,

Do you really need a special voltage regulator even after the pi filter?  My gut feeling tells me that a 60 volt spike would be considerably tamed by the pi filter, and that a standard voltage regulator would work.  I'm only asking because I've done this and so far haven't had any problems.  Are you using the super regulator just in the event of some kind of failure in the ignition system - as a last line of defense?

GCataldo,

The pi filter itself is a general structure, and whether it will work with your requirements depends on the components you select - but not the component values.  So be sure the chokes you buy are rated for more than 1.5 amps and be sure the capacitors are rated for more than 5 volts.

As for switching regulators, you may want to consider it if you are using 1.5 amps.  A linear regulator dropping 12 volts to 5 volts will be dissipating 10.5 watts as heat.  A decent switching regulator will dissipate less than a watt.

[glork]

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rhinoceroshead wrote:

Glork,

Do you really need a special voltage regulator even after the pi filter? My gut feeling tells me that a 60 volt spike would be considerably tamed by the pi filter, and that a standard voltage regulator would work. I'm only asking because I've done this and so far haven't had any problems. Are you using the super regulator just in the event of some kind of failure in the ignition system - as a last line of defense?

GCataldo,

The pi filter itself is a general structure, and whether it will work with your requirements depends on the components you select - but not the component values. So be sure the chokes you buy are rated for more than 1.5 amps and be sure the capacitors are rated for more than 5 volts.

As for switching regulators, you may want to consider it if you are using 1.5 amps. A linear regulator dropping 12 volts to 5 volts will be dissipating 10.5 watts as heat. A decent switching regulator will dissipate less than a watt.

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Hi Rhino.
The 60V transient spec was something I read in an automotive document some time ago. Either it didn't say or I don't remember transient pulse-width information, so I just play it safe and assume most of it will go thru the filter. I could easily be wrong (depending, of course, on the specifics of said filter).

As for the regulator I agree with you completely. At 1.5A load this is no place for a linear. I use lowl-side (low-voltage) switchers all the time. Today's devices are highly integrated, well mannered and really easy to use.

Additionally, and I never vary this even for cost sensitive products, I use a 1.0uH smt inductor feeding 4.7uF || 0.1uF caps as close as I can get them to the Vdd pin(s) of the micro. I've never felt it is wasted.
ron