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info@ckmintech.com
Joined: 16 May 2006
Posts: 39
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| 12f629 power-on-reset |
 Posted: Fri Dec 08, 2006 9:20 am |
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A 12f629 is runing on 6V, 4Mhz internal oscillator and MCLR enabled and connected a 10K resistor to VDD (+6V ). I found that somtime it was not start to run after power up until MCLR was set to low to reset it.
I think setting power on reset can solve this problem but I am not sure how to do this. Is it fuse PUT?
Any advise?
Thanks |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Dec 08, 2006 11:09 am |
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It's likely that you need the BROWNOUT fuse.
Also, the 12F629 is not rated to run at 6.0 volts.
The data sheet shows that the Absolute Maximum Rating is 6.5v.
This is in section 12.0 of the data sheet.
http://ww1.microchip.com/downloads/en/DeviceDoc/41190c.pdf
There is+ a notice in a gray box, in that section:
| Quote: |
This is a stress rating only and functional operation of the device
at those or any other conditions above those indicated in the operation
listings of this specification is not implied. |
In section 12.1, DC Characteristics, the chip is only specified to
operate at a maximum of +5.5v for Vdd. So if you run it at 6v,
you're running it out of spec and there's no guarantee that it will
work properly. It may work. It may be OK in a hobby situation,
but I would never ship a product that way. |
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info@ckmintech.com
Joined: 16 May 2006
Posts: 39
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| Posted: Sat Dec 09, 2006 3:35 am |
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Thnaks for the advise.
BOD is not suitbale for my design because it will use 109 uA at 5V which is far too much for my power budget.
I put 2 1N4148 to drop the voltage from 6V to 4.8V. |
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