I want to design 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.
Is this possible?
Electronic – How to implement a soft power switch controllable by microcontroller
designmicrocontrollerpower supply
Related Solutions
This is variation on my answer to this question. Like Mike, I am also using a P-channel MOSFET. The OP stated: "The Voltage regulator requires Vin +/- 0.3V on the Enable Pin", and "MicroController Output Pin High state is 2.7V Max". Therefore when the battery voltage is above 2.7v, the µC will be unable to supply the required voltage to meet the voltage spec for the Enable lead. So I am using the control lead of the µC to control the MOSFET, which in turn switches the battery voltage (or Vin) to the Enable lead.
Initially, the control lead from the µC is configured as an input. When the button is pressed, battery power is applied through a Schottky diode (keep Vf below 0.3v) to enable the regulator. The µC then configures the control lead as an output and grounds it, keeping the enable lead high through the MOSFET (which keeps the voltage at the battery level). Meanwhile, the button can be used as an input.
The circuit should draw very little power (less than 1 µA) when the µC is powered down, assuming the regulator shuts down completely when the Enable lead is low.
This eliminates the cost of the LTC2954 chip which runs over $2 in 500 unit quantities. This circuit should be under 10 cents in quantity (except for the switch and regulator).
Based on the circuit you provide, you could just add a diode in series right after the switch (S1) (cathode connected to the switch) and them you could use an input to detect if the switch was pressed again, if so, turn off PB3.
The zener diode protects the PIC input from the voltage coming from the power supply.
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Best Answer
This example uses a Maxim MAX1835 step-up regulator, but could be applied to others as well that have a shutdown pin.
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 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.