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Always ON Power Design! 
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LQFP144 - On Top Of The Game
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Joined: Tue Mar 02, 2010 2:33 pm
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Could we maybe incorporate a 5v supervisory/monitoring IC to the CPU RESET pin perhaps? If our CPU doesnt have voltage monitors internally,etc.

Microchip have good ones, MCP120-450 is the one I have had good experience with.

http://au.element14.com/microchip/mcp12 ... dp/9758429


Thu Jul 14, 2011 3:52 am
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I'm pretty sure it's well behaved in this way. We can do some testing soon, we being someone, maybe even me, though someone with a variable supply would be a better candidate.

The CPU has a low V interrupt which I handle (and don't do much with other than count events). I've never seen it fail to come up, BUT, I've never had it be asleep when the power has gone low. If I leave that interrupt enabled when asleep, it should trigger a wake up also, I think. If that's true, then it will behave just the same as every other time.

So yes, 99.9999% sure it's a non-issue, but thanks for pointing it out, Marcos!

Fred.

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Thu Jul 14, 2011 7:35 am
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Why not to just use a built-in ignition switch controlled LDO such as LM9070 to wake up MCU first?
http://www.ti.com/lit/ds/symlink/lm9070.pdf
Then the MCU starts to control of the other actuator power.


Sat Jan 28, 2012 8:47 am
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That doesn't actually solve the problem, and offers a feature that we don't need, IE, controlled turn off. The idea is to _never_ turn off, and to just go to sleep and wake up. Resets can be performed through software to switch states and/or reset the device to give it a fresh start. That document, though, has an example circuit for the power input, which I've captured here:

Image

They clearly do not use something with hysteresis on the input to the micro, which is likely a good example to follow, for the aforementioned reasons of ending up locked out without a key cycle.

I'll be doing some testing on this circuit and code in the next month or so, just in time for RavAGE layout, so stay tuned.

Fred.

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Sat Jan 28, 2012 11:17 am
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As i know there are already good solutions for Power Supply.

I got a LM2984T on my OEM ECU pcb, i think it is very exotic but there should be similar solutions

Picture is stolen somewhere from the internet :lol:

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Thu Aug 01, 2013 7:34 am
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Fred wrote:
What I intended to convey was that the stuff INSIDE the ECU should be controlled by key and not by CPU. In the diagram there are 8 relays, in two banks. The two banks are: 1) is key switched and controls various power feeds to the ECU and accessories such as wideband etc 2) is ECU switched and controls fuel pumps and power to coils and injectors. Somewhere on the forum is a list of what all the fuses and items are and are for, hence the letter/number labeling scheme. I'm not trying to say that various external accessories can't/shouldn't be controlled by CPU. As noted there are valid cases for external CPU controlled power, such as cooling fans, pumps, etc that you want to keep working after shut down.

Fred.


You can also allow CPU to override for those 'key' controlled power like fan, pumps, etc. Just OR them together and have both.


Wed Dec 18, 2013 7:09 am
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