LTC2952IFPBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2952IFPBF' PDF : 30 Pages View PDF
LTC2952
APPLICATIONS INFORMATION
Aborted Power-On Sequence
The power-on sequence is aborted when the μP fails to
set the KILL pin high before the 500ms KILL On Blanking
time expires, as shown in the timing diagram in Figure 11.
When the KILL On Blanking timer expires (t7), the KILL
pin is still low indicating that the μP/system has failed to
power on successfully. When the system failed to set the
KILL pin high within the specified 500ms time window,
the LTC2952 pulls the EN pin low (thus turning off the
DC/DC converter) and as a side effect resets the internal
ON/OFF signal.
KILL Power Turn-Off During Normal Operation
Once the system has powered on and is operating nor-
mally, the system can turn off power by setting KILL low,
as shown in the timing diagram in Figure 12. At t9, KILL is
set low and this immediately causes the LTC2952 to pull
EN low, turning off the DC/DC converter.
Extended Power During Turn-Off
In the shutdown process, the availability of power can be
extended by providing edges to the WDE pin during the
KILL Off Wait time. The timing diagram in Figure 13 is
similar to the power-on/power-off sequence timing diagram
(Figure 10) except for the edges on the WDE pin during the
shutdown process. At time t10, the internal ON/OFF signal
transitions low. When this happens, the DC/DC converter
providing power to the system will be shut off in 500ms
unless the WDE pin is toggled.
When the WDE pin transitions at t11, the LTC2952 resets
the 500ms KILL Off Wait timer. Before this second 500ms
wait time expires, the WDE pin transitions again (this time
from high to low) at t12, causing the 500ms timer to reset
again. Finally, the third 500ms timer which starts at t12
expires without any further extension at t13 causing the
EN pin to go low, shutting down the DC/DC converter.
INTERNAL
ON/OFF SIGNAL
KILL
DON'T CARE
EN
t8
t9
tKILL, ON BLANKING
Figure 12. KILL Initiated Shutdown
INTERNAL
ON/OFF SIGNAL
KILL
DON'T CARE
EN
2952 F12
t7
tKILL, ON BLANKING tEN, LOCKOUT 2952 F11
Figure 11. Aborted Power-On Sequence
INTERNAL
ON/OFF SIGNAL
KILL
DON'T CARE
EXTENDED HOUSE KEEPING TIME
DON'T CARE
EN
WDE
t10
t11
t12
t13
tKILL, ON BLANKING < tKILL, OFF WAIT
tKILL, OFF WAIT tEN, LOCKOUT 2952 F13
< tKILL, OFF WAIT
Figure 13. Power-On/Power-Off Sequence with Extended Shutdown/Housekeeping Wait Time
2952fa
21
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