LTC2956
7
2956fa
For more information www.linear.com/LTC2956
PIN FUNCTIONS
EN: Enable Output (LTC2956-1). EN is an active high output
to control the turn-on/off of a load. Connect this pin to
the RUN or SHUTDOWN pin of a voltage regulator. The
LTC2956-1 pulls EN high through an internal 900k resis-
tor and Schottky diode to a 3.3V regulated supply when
the pushbutton is pressed or when the wake-up period
is reached. EN pulls low during the Sleep state. This pin
may be left open if unused.
EN: Inverted Enable Output (LTC2956-2). 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 directly.
In the Sleep state, the LTC2956-2 pulls this pin to V
IN
through an internal 900k resistor. The LTC2956-2 pulls
EN to GND when the pushbutton is pressed or when the
wake-up timer period is reached. This pin may be left
open if unused.
Exposed Pad (QFN only): Exposed Pad. Leave open or
connect to device ground.
GND: Device Ground.
LONG: Long Power Down Time Selection Input. Connect a
resistor from the LONG pin to GND. Together with the 100k
resistor between the RANGE and LONG pin, this adjusts
the t
LONG
power down time (t
LONG
can be adjusted from
128ms to 16.4s). If SLEEP is pulled high or PB is pulled
low longer than t
LONG
, the part goes into SHUTDOWN
mode. See Applications Information for details.
OFFALERT: Off Alert Open Drain Output. The LTC2956
pulls this pin low for 1 second (t
OFF
) whenever the part
goes from RUN mode to SHUTDOWN mode. This pin can
be connected to the interrupt input of the system (with a
pull-up resistor to the system supply) to alert the system
before shutdown. It can also be used to drive an external
LED to give a visual indication. This pin may be left open
if unused.
ONALERT: On Alert Open Drain Output. The LTC2956 pulls
this pin low whenever the part goes from SHUTDOWN
mode to RUN mode. The pin stays low while the EN pin
is high and it can be used as an input to the system to
request for initial boot up routine. This pin may be left
open if unused.
ONMAX: Maximum Awake Timer Capacitor Input. Connect
a capacitor from this pin to GND adjust the maximum
allowed awake time (t
ONMAX
) at 13.3ms/nF. If this pin is
left floating, the minimum awake time is limited to 8ms.
Tie this pin to GND if unused.
PB: Pushbutton Input. This is an active low input with a
900kΩ pull-up to an internal 3.3V regulated supply. Con-
nect one terminal of the pushbutton switch to this pin and
connect the other terminal of a pushbutton switch to GND.
The pin may be left open if unused.
PBOUT: Debounced Pushbutton Open Drain Output. This
pin follows the debounced PB input. This pin may be left
open if unused.
PERIOD: Wake-Up Timer Adjust Input. Connect a resistor
from the PERIOD pin to GND to adjust the wake-up timer
period. See the Application Section for resistor selection
information.
RANGE: Wake-Up Timer Range Selection Input. Connect a
resistor from the RANGE pin to GND and a
100k resistor
between the RANGE and LONG pin to choose the wake-
up timer period range setting. See Application Section for
information about the resistor selection.
SLEEP: SLEEP Input. The SLEEP input is active during
RUN mode. In the Awake state, a falling edge at the SLEEP
input will pull EN low (EN high) and put the system into
the Sleep state. If the SLEEP input goes high during the
Sleep state, the LTC2956 re-enters the Awake state and
pulls EN high (EN low) to turn on the system. Holding
SLEEP high for more than t
LONG
will force the system into
the SHUTDOWN mode. If unused, tie SLEEP to GND, and
use the ONMAX pin to control the awake time.
V
IN
: Power Supply Input (1.5V to 36V).
