Pushbutton On/Off Controller with Failsafe Voltage Monitoring：Have you had the exasperating experience of a laptop or
PDA defi antly not responding to your commands? You
frantically press key after key, but to no avail. As hope
turns to anger (but just before you throw the company’s
laptop through the window) you slam your fi nger against
the on/off power button. Ten seconds later, your laptop
fi nally surrenders and the screen goes black in a high
pitched whimper.
The unresponsive pushbutton was likely the result of an
unresponsive μP or system logic—as evidenced by the
crash. By pressing and holding the on/off pushbutton,
the LTC2953 provides the user with the ability to force
system power off, even under fault conditions. This long
pushbutton command works independently of system
logic and automatically shuts off power after the adjustable
timer expires. The length of time the pushbutton must
be held low in order to force a power down is adjustable
with an external capacitor on the PDT pin.