atmega16 adc question

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Mark Contact options for registered users 's Avatar (by Gravatar) posted on
November 9, 2005, 11:20 pm
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I'm working on a project using an Atmega16 mcu. It's adc is being used to
measure the battery voltage via a divider. A potential problem is that when
the board is switched on there is a short time that the voltage is applied
to the adc pin before the switching power supply brings the mcu up. My
question is whether this is a problem, and if so how to solve it. Thanks for
your assistance.

Mark




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Mark Contact options for registered users 's Avatar (by Gravatar) posted on
November 9, 2005, 11:23 pm
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Re: atmega16 adc question



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I should have added that I'm using a pmos switch to turn the switcher on. A
pushbutton switch turns on the pmos switch, and a line from the mcu (via a
diode) latches it on.

Mark



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Christian Contact options for registered users 's Avatar (by Gravatar) posted on
December 6, 2005, 2:20 pm
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Re: atmega16 adc question


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Why should that be a problem? AD-conversion starts as you set the corresponding
bit. As long as you don't exceed the absolute maximum voltage and thus damage
the device I don't see any problem.

Christian

Anthony C Smith Contact options for registered users 's Avatar (by Gravatar) posted on
December 8, 2005, 8:16 am
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Re: atmega16 adc question



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to
applied
on. A
a
corresponding
damage

The problem is that the mega is a cmos device, and you can cause SCR
latchup, potentially killing the chip-
the mega has protection diodes from the pins to the supply rails, this is
sufficient if the top resistor of the divider is >100K ohms; if not maybe
add 2 schotkey diodes from the pin to the supply rails to help the small
internal diodes out.
regards

Anthony C Smith MAES MinstSCE



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