How to implement a soft power switch controllable by microcontroller

Posted on Feb 6, 2014

A circuit such that the microcontroller can toggle a GPIO pin and shut the whole system (including microcontroller itself) down. And when the user presses a momentary button, the power is brought back up again. The circuit is normally powered down. When the user presses the pushbutton, the battery is fed into the -SHDN pin, enabling the regulator and turning

How to implement a soft power switch controllable by microcontroller
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on the 3. 3V to the microcontroller. The microcontroller then puts a logic 1 on the POWER ON lead, holding the power on after the user releases the pushbutton. When the microcontroller wants to shut itself off, it sets the POWER ON lead to 0. @Kortuk, good point. I was assuming the micro would turn on fast enough that it could override the switch before the first bounce, assuming driving the pin high was the first thing the micro did. If that isn`t the case, one could add a capacitor on the -SHDN lead to create a time constant for the turn on (although this would also introduce a slight delay in turn off). The 10 nF one probably needs to be left in for noise suppression (it was included in a datasheet sample schematic). Or one could add additional RC circuit for just the switch. tcrosley Jan 14 `11 at 16:36 A bigger issue that switch bounce is processor behavior during power-down. In particular, it may be good to make sure that the processor can only turn the supply on when its VDD is above the point where correct operation is guaranteed. I`ve had to tweak some auto-power-down circuits that would occasionally fail as a consequence of the processor running random code when VDD fell below the valid operating voltage. The random code could set the "power on" output high, which would in turn power the device back up, running code at a random address. supercat May 30 `11 at 1:45

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