Datasheet LTC2951-1, LTC2951-2 (Linear Technology) - 10

LTC2951-1/LTC2951-2
APPLICATIONS INFORMATION Description Turn-Off
The LTC2951 is a low power (6µA), wide input voltage range To initiate a power-off sequence, PB must be held low for a (2.7V to 26.4V), pushbutton On/Off controller that can in- minimum of 32ms (tDB, OFF). Additional turn-off debounce terface to a µP and a power supply. The part incorporates time may be added via an optional capacitor connected all the flexible timing needed to debounce the pushbutton to the OFFT pin (tOFFT). The following equation describes input (PB). The LTC2951 also provides a simple interface the additional time that PB must be held low to initiate a (INT output, KILL input) to allow a system to power on and power-off sequence. COFFT is the OFFT external capacitor: power off in a controlled manner. The wide input voltage C range allows a system designer to operate from single cell OFFT = 1.56E-4 [µF/ms] • (tOFFT – 1ms) to multi-cell battery stacks. Very low quiescent current Once PB has been validly pressed, INT is switched low. makes the LTC2951 ideal for continuously monitoring the This alerts the µP to perform its power-down and house- on/off pushbutton of a handheld device. keeping tasks.
Turn-On KILL Turn-Off Delay
When power is first applied to the LTC2951, the part initial- The LTC2951 provides a failsafe feature that allows the izes the output pins. Any DC/DC converters connected to user to turn off system power (via PB) under system fault the EN/EN pin will, therefore, be off. To assert the enable conditions. During a normal power-down sequence, the output, PB must be held low for a minimum of 128ms LTC2951 first interrupts the µP by setting INT low. The (tDB, ON). µP then performs power-down and housekeeping tasks Once the enable output is asserted, any DC/DC converters and drives KILL low when done. The LTC2951 releases the connected to this pin are turned on. The KILL input from enable output, thus turning off system power. The KILL the µP is ignored during the succeeding 512ms blanking turn-off timer starts when INT is driven low. If the µP fails time (tKILL, ON BLANK). This blanking time represents the to respond during this timeout period, the enable output maximum time required to power up the DC/DC converter will automatically release. The default power-down timeout and the µP. If KILL is not brought high during this 512ms period is 128ms (tKILL, OFF DELAY), which can be extended time window, the enable output is released. The assumption by placing an optional capacitor on the KILLT pin (tKILL, is that 512ms is sufficient time for the system to power up. OFF DELAY, ADDITIONAL). The following equation describes the additional power-down timeout period. CKILLT is the KILLT external capacitor: CKILLT = 1.56e-4 [µF/ms] • (tKILL, OFF DELAY, ADDITIONAL – 1ms) Note that KILL can be driven low (thereby releasing the enable output) at any time after tKILL, ON BLANK period. 295112fb 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Timing Diagrams Applications Information Typical Applications Package Description Revision History Typical Application Related Parts