Power-On Initialize

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danlee58
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Joined: Thu Jan 17, 2013 2:29 am

Power-On Initialize

Post by danlee58 » Fri Dec 26, 2014 8:04 pm

My SuperPro board in my controller, doesn't always initialize when external power is applied to J4. It always works when powered through the USB dongle. I can't get to the reset button to reset it after power-on, I need to insure that the board initializes when power is applied.



AMDlloydsp
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Re: Power-On Initialize

Post by AMDlloydsp » Fri Dec 26, 2014 9:42 pm

Are you sure your power is coming up cleanly, and with a good fast rise-time?

Jittery supply switching can muck things up pretty bad. A mechanical switch on the DC leg is about the worst way to turn power on and off. Switching the AC side of a ac/dc power supply is usually fine.

Lloyd

danlee58
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Joined: Thu Jan 17, 2013 2:29 am

Re: Power-On Initialize

Post by danlee58 » Sun Dec 28, 2014 10:24 pm

The power is from a 12 Volt battery source through a DC-to-DC converter that regulates it to 7.0 Volts, and that is connected to the J4 connector. I experience the problem when I connect to a 12 Volt stack of AAs or switch on the 12 Volt vehicle power. There are some pull-up resistors on the 5 Volt line.

Do I need some Delay to the Reset line?

AMDlloydsp
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Re: Power-On Initialize

Post by AMDlloydsp » Mon Dec 29, 2014 12:55 am

Hmmm... I assume the 7V output is directly connected to J4 without a switch?

Did you put a de-glitching cap across that 7V line? Some high-frequency converters will issue a jittery spike upon power-up, and de-glitching is the solution. Probably something under 0.1uf will do the trick, but you might look at the specs on the converter to make sure. I have them on my mother boards, and they (for instance, MuRata converters) require an external output cap.

I have never used the reset line on the SuperPro. I just power it up (cleanly, of course), and it resets reliably.

AMDlloydsp
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Re: Power-On Initialize

Post by AMDlloydsp » Tue Dec 30, 2014 12:29 pm

I just saw your statement, "There are some pullups on the 5V line".

Pullups for what, drawing how much current? Are they just logic-level pullups, or are they driving loads? Are these references for inputs? If so, consider using the 3.3V supply for your logic level references. And don't forget that the LPC1756 has programmable pullups on-chip.

Have you checked the actual voltage on the board when it's fed from your converter, as opposed to that voltage when running off the USB supply? Check at the output of the 5V regulator on the SuperPro.

Could it be that your converter is running low under load?

Lloyd

basicchip
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Re: Power-On Initialize

Post by basicchip » Tue Dec 30, 2014 11:05 pm

I like the OKI-78SR for 12V battery operation, they have a wide range of input voltage 7-36V so they are pretty robust, and it wouldn't take a lot of protection in an auto environment. I know there are others out there using our controllers in automotive environments and can comment with first hand experience.

What size pullups and what are they pulling to, and what is the state of the power supply at the time. Many of these little micros can be "powered" from their inputs as there are parasitic diodes in most push pull IOs. It is possible the part is never really turning off and hence not getting a good reset. It might be experiencing a brown out which you can also detect.

Also if you have big caps on the supply it could take a long time to discharge, which can affect turn on.

We really need more details on you actual configuration. A scope to trace on the supply with a long measurement time might give you a clue. The LPC1756 does have a RESOUT pin (on pin 11), although I did not hook it to a via, it should still be probable.

AMDlloydsp
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Joined: Mon Apr 15, 2013 3:51 pm
Location: NE Central FL

Re: Power-On Initialize

Post by AMDlloydsp » Wed Dec 31, 2014 12:06 am

Many of these little micros can be "powered" from their inputs as there are parasitic diodes in most push pull IOs. It is possible the part is never really turning off and hence not getting a good reset.
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Wow... Bingo! And I completely forgot about that! Shucks! You can even power LS-TTL that way, if you're not careful!

LLoyd

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