LTC2954IDDB-1#TRMPBF Linear Technology, LTC2954IDDB-1#TRMPBF Datasheet - Page 11

• Manufacturer Part Number: LTC2954IDDB-1#TRMPBF
• Description: IC PUSH BUTTON ON/OFF CTRLR 8DFN
• Manufacturer: Linear Technology

Specifications of LTC2954IDDB-1#TRMPBF

• Applications: Push Button, On/Off Controller
• Voltage - Supply: 2.7 V ~ 26.4 V
• Current - Supply: 6µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Other names: LTC2954IDDB-1#TRMPBFTR

APPLICATIONS INFORMATION
low 512ms after it went high. Note that the LTC2954 does
not sample KILL and PB until after the 512ms internal timer
has expired. The reason PB is ignored is to ensure that
the system is not forced off while powering on. Once the
512ms timer expires (t
debounced with an internal 32ms timer. The system has
now properly powered on and the LTC2954 monitors PB
and KILL for a turn-off command while consuming only
6μA of supply current.
A high to low transition on PB (t
sequence debounce timer. In order to assert the interrupt
output (INT), PB must stay low continuously (PB high
resets debounce timer) for 32ms (t
tion of the power-down debounce timer (t
interrupt timer keeps the interrupt output low for at least
32ms, even if PB is released between t
low at the end of this 32ms internal timer (t
adjustable power-down timer is started. The capacitor
placed at the PDT pin will determine the time period of
this timer. If the pushbutton is released prior to 16 cycles
of the PDT pin, the interrupt output will go high (t
that the enable output is not directly changed by this
interrupt pulse. The function of the interrupt signal is to
initiate a software shutdown. At t
its power-down functions and asserted the KILL input
low. This releases the enable output, which in turn shuts
down system power. Note that if the pushbutton is held
long enough to count 16 cycles at the PDT pin, the enable
pin would be released immediately after the 16th cycle.
The system is now in its reset state where the LTC2954 is
in low power mode (6μA) and PB is monitored for a high
to low transition.
KILL
PB
EN
Figure 3. μP Turns Off Power (LTC2954-1)
XXX DON’T CARE
4
), the release of the PB pin is then
9
5
, the μP has performed
) starts the power-off
6
–t
5
). At the comple-
6
and t
7
6
), the external
KILL LOW
), an internal
μP SETS
TURNS OFF
t
7
KILL
DC/DC
. If PB is
8
2954 F03
). Note
PB BLANKING
(INTERNAL
SIGNAL)
Aborted Power-On Sequence
The power-on sequence is aborted when the KILL remains
low at the end of the 512ms blanking time. Figure 2 is a
simplified version of an aborted power-on sequence. At
time t
turning off the DC/DC converter).
μP Turns Off Power During Normal Operation
Once the system has powered on and is operating nor-
mally, the μP can turn off power by setting KILL low, as
shown in (Figure 3). At time t
μP . This immediately pulls EN low, thus turning off the
DC/DC converter.
DC/DC Turn Off Blanking
When the DC/DC converter is turned off, it can take a sig-
nificant amount of time for its output to decay to ground. It
is desirable to wait until the output of the DC/DC converter
is near ground before allowing the user (via PB) to restart
the converter. This condition guarantees that the μP has
always powered down completely before it is restarted.
Figure 4 shows the μP turning power off. After a low on
KILL releases enable, the internal 256ms timer ignores the
PB pin. This is shown as t
KILL
PB
EN
ABORT
Figure 4. DC/DC Turn-Off Blanking (LTC2954-1)
XXX DON’T CARE
, since KILL is still low, EN pulls low (thus
POWER ON
EN/EN, LOCKOUT
KILL
TURNS OFF
, KILL is set low by the
DC/DC
LTC2954
in (Figure 4).
t
EN/EN, LOCKOUT
PB IGNORED
256ms
μP SETS
KILL LOW
11
2954 F04
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