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
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
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
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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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