Datasheet

LTC2951-1/LTC2951-2
12
295112fb
Figure 2. Aborted Power-On Sequence for LTC2951-1
and the external OFFT capacitor (t
6
–t
5
). At the completion
of the OFFT timing (t
6
), an interrupt (INT) is set, signify-
ing that EN will be switched low after the KILL turn-off
(t
KILL
,
OFF DELAY
+ t
KILL
,
OFF DELAY, ADDITIONAL
) timeout
period. Once a system has finished performing its power-
down operations, it can set KILL low (t
7
) and thus imme-
diately set EN low, terminating the KILL turn-off timer. The
release of the PB pin is then debounced with an internal
32ms timer.
The system is now in its reset state: where the LTC2951
is in low power mode (6µA). PB is monitored for a high
to low transition.
Figure 3. µP Turns Off Power (LTC2951-1)
APPLICATIONS INFORMATION
PB
KILL
POWER-ON
TIMING
EN
512ms
INTERNAL
TIMER
POWER
TURNED OFF
2951 F02
µP FAILED TO SET
KILL HIGH
t
DB, ON
t
ABORT
PB & KILL IGNORED
PB
EN
DC/DC
TURNS OFF
2951 F03
KILL
XXX DON’T CARE
µP SETS
KILL LOW
t
KILL
Aborted Power-On Sequence
The power-on sequence is aborted when the KILL remains
low after the end of the 512ms blanking time. Figure 2 is
a simplified version of an aborted power-on sequence.
At time t
ABORT
, since KILL is still low, EN pulls low (thus
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
KILL
, KILL is set low by the µP.
This immediately pulls EN low, thus turning off the DC/
DC converter.