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EN: Enable Output (LTC2955-1). EN is an active high output
to control the turn-on/off of the system power. Connect this
pin to the RUN or SHUTDOWN pin of the voltage regulator.
The LTC2955 asserts EN high when the pushbutton is
pressed or when ON goes high. The output high voltage
follows the internal LDO output which provides sufficient
margin for most SHUTDOWN pin thresholds.
EN: Inverted Enable Output (LTC2955-2). EN is an active
low output to control the turn-on/off of the system power.
It may drive a voltage regulator’s active low enable input,
or it may drive the gate of a P-channel MOSFET. In the
turn-off state, the LTC2955 pulls this pin to VIN through
an internal 900k resistor. The LTC2955 pulls EN to GND
when the pushbutton is pressed or when ON goes high.
Exposed Pad (DFN only): Exposed pad. Leave open or
connect to device ground.
GND: Device Ground.
INT: Open Drain Interrupt Output. Connect this pin to the
interrupt input of the system with a pull-up resistor to the
system supply. The LTC2955 asserts the INT pin low when
it receives the turn-off command from the pushbutton or
the ON pin. The minimum pulse width of the INT signal is
32ms and can be extended through the TMR pin.
KILL: Kill Input. A low at KILL releases the enable output
(EN/EN). This pin can be driven by the microprocessor or it
can be used as a voltage monitor input. Tie to the system
power supply or an external voltage of 1.2V~5V if unused.
ON: Monitor Input. Connect this pin to an external resistive
divider from the monitored voltage. This allows automatic
system turn-on when the monitored voltage transitions
high. For the DFN part, if the SEL pin is tied high, it also
allows automatic system turn-off when the monitored
voltage transitions low. Tie to GND if unused.
PB: Pushbutton Input. This is an active low input with a
900k pull-up to an internal LDO. Connect one terminal of
the pushbutton to this pin and connect the other terminal of
the pushbutton to GND. The pin may be left open if unused.
PGD (DFN only): ON Status Output. A high on this pin
indicates that the voltage at the ON pin is above the input
threshold of 0.8V. This pin can be used as a system input
to inform the system whether the turn-on was triggered by
the ON pin or the pushbutton pin. Leave open if unused.
SEL (DFN only): Mode Select Input. Connect SEL to GND
to block the ON pin falling edge from activating system
turn-off. Connect SEL to VIN to allow both the ON pin rising
and falling edges to activate system turn-on and turn-off
respectively. For the TSOT package, SEL is internally tied
to GND. Do not leave open.
TMR: Timer Pin. A capacitor to ground determines the
additional time (5.2 seconds/μF) beyond the default 64ms
that the pushbutton must be held low before immediately
releasing the EN/EN and INT outputs. The turn-off debounce
time defaults to 64ms if this pin is left open. To disable the
ability to force a system power-down with a pushbutton
press, ground the TMR pin.
VIN: Power Supply Input. For > 20V applications, connect
VIN to the power source through a 1k resistor and bypass
VIN to GND with a 10nF low ESR capacitor.