Today, simplicity and minimum controls is required for design of a handheld device. It will be very useful if a circuit allow us to turn the power on or of with a single push button. A single-pushbutton power control circuit that consist of only a few small components, and consumes little power is shown on circuit diagram below.
A debouncer (the MAX6816, IC1)is connected with a normally open (NO) single-contact pushbutton. This will guarantees a single output edge (rise or fall) each time the button is pushed or released. The clock input of a flip-flop (IC2) wired as a T-type 9toggle) flip-flop is driven by MAX6816’s output. A low-dropout (LDO) linear regulator (the MAX6484,IC3) is controlled by the flip-flop output. A handheld gadget is powered by MAX6484, which turns on or off each time that the pushbutton is operated. If the regulator features a logic-level power management input, the same circuit can also drive other types of power regulator.
To ensure that the circuit always powers up in the same state (OFF) when PWR_IN is connected firts, there is 1Mohm resistor and 100nF capacitor connected to the flip-flop’s CLR input. The operation range of the ON/OF control circuit (pushbutton, debouncer, and flip-flop) is 2V to 5.5V. When the supply voltage is 3.5 V, it draws about 3.5uA. You can buy MAX6816 in a4-pin SOT143 package, IC2 in an MO-187 package, and the MAX6484 in a 6-ball UCSP™ package. [Source: MAXIM Application Note]