DEMO MANUAL DC2254A
LTC2956
Wake-Up Timer
with Pushbutton Control
Description
Demonstration circuits 2254A-A and 2254A-B feature the
LTC2956-1 and LTC2956-2, respectively. The
LTC
®
2956
is a micropower, wide input voltage range, configurable
wake-up timer with pushbutton control. It periodically
wakes up and turns on a connected system to perform
tasks like monitoring temperature or capturing images.
After completing the task, the LTC2956 turns the system
off to conserve power. The wake-up timer period can be
adjusted from 250ms to 39 days.
The DC2254A allows easy access to all the pins necessary
to configure the device. Onboard jumpers, and an 8-pin
DIP switch provide a range of value options, to set the
wake-up timer, wake-up timer period and long power down
time. Turrets are also present, allowing direct access to all
the pins present on the LTC2956 to allow easy interfacing
with a system with arbitrary requirements.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2254A
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
BoarD photo
+
PSU
–
I/O TO
SCOPE OR
µP
Figure 1. Test Equipment Setup
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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.
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dc2254af
DEMO MANUAL DC2254A
operatinG principLes
Connect a 1.6V to 36V power supply to VIN. If VIN is
less than 5.5V then set the LDO_IN jumper to EXTERNAL
and connect a 5.5V to 35V supply to the LDO_IN turret.
The LTC2956 will still operate with no power applied to
LDO_IN, but monitor LEDs will not function.
RUN AND SHUTDOWN MODE
The LTC2956 has two modes of operation: RUN mode
and SHUTDOWN mode.
In RUN mode, the LTC2956 cycles between the Awake
state and the Sleep state with a period of t
PERIOD
which
is set by the RANGE TIME PERIOD jumper. During the
Awake state, the EN/EN pin is asserted to turn the system
on, and the t
ONMAX
timer runs. The t
ONMAX
timer can be
configured with the AWAKE TIMER jumper. The LTC2956
exits the Awake state when a falling edge is detected on
the
SLEEP
pin or if the t
ONMAX
timer expires. In the Sleep
state the EN/EN output stays de-asserted. The LTC2956
only returns to the Awake state when the t
PERIOD
time
is reached, pushbutton is pressed or if a logic high is
detected on the
SLEEP
pin. The LTC2956 can be put into
SHUTDOWN mode if the pushbutton is held low for longer
than a user defined t
LONG
period.
The SHUTDOWN mode is a very low power mode with the
timer disabled, entered through a press of the pushbut-
ton or a high pulse at the
SLEEP
input which lasts longer
than t
LONG
. A short press on the pushbutton brings the
LTC2956 back into RUN mode.
On power up, the LTC2956 can be initialized to either of
these two modes. SW1 provides 8 different options to
initialize the part as shown in Table 1.
Table 1. SW1 Configuration Table
SW1 POSITION
1
2
3
4
5
6
7
8
MODE
SHUTDOWN
SHUTDOWN
SHUTDOWN
SHUTDOWN
RUN
RUN
RUN
RUN
TLONG
0.128s
0.512s
1.024s
2.048s
0.128s
0.512s
1.024s
2.048s
ONALERT
AND
OFFALERT
SIGNALS
The
ONALERT
signal pulls low when the LTC2956 enters
RUN mode from SHUTDOWN. This signal is useful to allow
connected systems to run initialization tasks.
The
OFFALERT
signal pulls low when the LTC2956 enters
SHUTDOWN mode from RUN mode. When the
PB
pin is
held low for a time longer than t
LONG
during RUN mode, the
LTC2956 first pulls the
OFFALERT
pin low which lasts for
t
OFF
(1s typ). Once the t
OFF
timer completes, the LTC2956
transitions to the SHUTDOWN mode.
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DEMO MANUAL DC2254A
operatinG principLes
PBOUT
250ms TIME PERIOD
EN
20ms AWAKE TIME
Figure 2. LTC2956-1, Awake Time Set to 20ms, Time Period Set to 250ms
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dc2254af
DEMO MANUAL DC2254A
operatinG principLes
PBOUT
EN
ONALERT
Figure 3. LTC2956-1, Awake Time Set to 20ms, Time Period Set to 250ms, Showing Proper Turn On Sequence with
ONALERT
Signal
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