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dc2254af
DEMO MANUAL DC2254A
Dc2254a tUrret anD JUMper DeFinitions
JUMPER AND SWITCH SETTINGS
RANGE TIME PERIOD (JP2):
Sets the time period between
enable signal assertions. The two available options pres-
ent on the board are 250ms and 1s. See Applications
Information in the LTC2956 data sheet and replace R11
and/or R12 if another time is desired.
AWAKE TIMER (JP1):
Sets the time the enable signal stays
asserted. The onboard capacitor can be used for an awake
time of 19.9ms or an external arbitrary capacitor can be
used to set a user defined enable time. The maximum
allowed awake time is set at 13.3ms/nF.
LDO_IN (JP3):
Choose the input to the onboard LT3060
regulator. It can either be set to INT to have it connected
to the VIN pin, or EXT in order to have it driven by the
LDO_IN turret. See the Operating Principles section. Only
for LED/Monitor circuitry.
SW1:
This 8 pin DIP switch can be used to initialize the
part in either RUN or SHUTDOWN mode and also allows
configuration of the t
LONG
time. See Applications Infor-
mation in the LTC2956 data sheet for more information.
SW2:
This pushbutton switch controls the input to the
PB
pin. This is an active low input with a 900kΩ pull up to an
internal 3.3V regulated supply. When the pushbutton is
pressed, EN/
EN
pin gets asserted after an initial debounce
time of 32ms.
EXTERNAL CONNECTIONS
Signal connections are made via the row of turret posts
along the edges of the board.
GND:
(3 Turrets) These turrets are connected directly to
the ground planes.
VIN:
Connect a 1.6V to 36V power supply to this turret.
ONMAX:
Connect a capacitor from this turret to GND if
an arbitrary awake time is desired. Use the relationship
t
AWAKETIME
= 13.3ms/nF. Set the AWAKE TIMER jumper
to EXTERNAL if using this turret.
PB
:
This turret is already driven by the pushbutton present
on the demoboard, however if needed it can be driven by
an external signal to simulate a pushbutton press.
LDO_IN:
Can be used to provide the LT3060 with power
when the LDO_IN jumper is set to EXT.
LDO_OUT:
Output from the LT3060. The state of this tur-
ret can be monitored by the LED labelled “LED SUPPLY”.
DIGITAL CONNECTIONS
EN/
EN
:
Active high (LTC2956-1) or active low (LTC2956-2)
signal. Should go active either with a debounced pushbut-
ton press or after a valid time period set by the RANGE
TIME PERIOD jumper.
ONALERT
:
This turret pulls low whenever the part goes
from SHUTDOWN mode to RUN mode. The signal stays
low while the EN/
EN
pin is asserted and it can be used as
an input to a system to request for initial boot up routine.
This turret may be left open if unused.
OFFALERT
:
This turret pulls low for 1 second whenever
the part goes from RUN mode to SHUTDOWN mode.
This pin can be connected to the interrupt input (with a
pullup resistor to the system supply) of a system to alert
the system before shutdown. This pin may be left open
if unused.
SLEEP
:
This turret is an input and is active during RUN
mode. In the Awake state, a falling edge at the
SLEEP
input
will de-assert EN/
EN
and put the system into the Sleep state.
If the
SLEEP
input goes high during the Sleep state, the
LTC2956 reenters the Awake state and re-asserts EN/
EN
to turn a system on. Holding this turret high for more
than t
LONG
(which is set by SW1) will force the LTC2956
into SHUTDOWN mode. See data sheet for more details.
PBOUT
:
This turret follows the debounced
PB
input. This
turret may be left open if unused.
