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atmega16 adc question

Discussion in '8bit Microcontrollers' started by Mark, Nov 9, 2005.

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  1. Mark

    Mark Guest

    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.

  2. Mark

    Mark Guest

    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.

  3. 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.

    Anthony C Smith MAES MinstSCE
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