POWER AND LINEAR IC SOLUTIONS

Multifunction Power Control with a Single Pushbutton

Today’s smart phones, PDAs (Personal Digital Assistants), laptops and PCs commonly feature power buttons that implement multiple functions, typically on/off as well as standby or hibernation. Pushbutton controllers, such as Linear Technology’s LTC2951 and LTC2954, support multiple function buttons in almost any electronic device.

The LTC2951 and LTC2954 are micro-power pushbutton on/off controllers with wide input voltage ranges between 2.7V and 26.4V to accommodate a variety of power supplies. Their very low quiescent currents, 6µA typical, perfectly suit battery powered applications. Designers can implement both power on/off and hibernation functionality using a single pushbutton and two pushbutton controllers.

The LTC2954’s enable output toggles system power, while an interrupt output provides de-bounced pushbutton status. In menu driven applications, the interrupt output can request a system power down and a power ‘kill’ input allows a microprocessor or system to reset the enable output, powering down the system. Independently adjustable On and Off timers allow dependable pushbutton control of the enable output and resistance to accidental toggling of system power.

Two versions of these devices are available to accommodate either positive or negative enable polarities.



In a typical LTC2951 application, its open-drain enable pin drives shut-down of the system’s DC/DC converter. The pin state toggles from a combination of pushbutton actuation and signals from the host microprocessor. To shut down the system when powered-up, the pushbutton needs to be held for the de-bounce time, either the controller’s 32ms default value or the period set using an external capacitor. An external capacitor can set the maximum allocated time for the processor to complete housekeeping tasks; alternatively, a designer can choose the LTC2951 default value of 128ms. To power up needs 128ms actuation.



The second illustration shows a circuit using two pushbutton controllers to provide power on/off and hibernation functionality using a single pushbutton.

The LTC2951's pushbutton input controls the toggling of an open-drain enable output. The pushbutton turn-off de-bounce time is externally programmable, while the turn-on de-bounce time is a fixed 128ms. A simple microprocessor interface allows proper system housekeeping before power down. Under system fault conditions, an adjustable ‘kill’ time-out delay ensures proper power down.

Features

• Adjustable pushbutton de-bounce, delay and power on/off timers
• Low supply current: 6µA
• Wide operating voltage range: 2.7V to 26.4V
• Options for circuit breakers or DC/DC converters
• Simple interface allows graceful MCU shut down
• High voltage pushbutton pin with internal pull-up
• ±10kV ESD human body model on pushbutton input
• Accurate 0.6V threshold on kill input
• Eight-pin 3mm × 2mm DFN and ThinSOT packages

Applications

• Pushbutton power path control
• Smart phones
• Portable instrumentation meters
• Blade servers
• PDAs
• Desktop and notebook computers

For further information, to register your interest in a Free Demo Board*, or to obtain a copy of the latest Altera/LTC Development Tools Brochure, please click here

* Free demo boards are limited to current or potential Arrow customers with valid opportunities and are at the discretion of local Arrow representatives.