LTC2952 Linear Technology, LTC2952 Datasheet - Page 21

• Manufacturer Part Number: LTC2952
• Description: Pushbutton PowerPath Controller
• Manufacturer: Linear Technology

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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 (t
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 t
set low and this immediately causes the LTC2952 to pull
EN low, turning off the DC/DC converter.
ON/OFF SIGNAL
INTERNAL
KILL
EN
DON'T CARE
Figure 12. KILL Initiated Shutdown
Figure 13. Power-On/Power-Off Sequence with Extended Shutdown/Housekeeping Wait Time
ON/OFF SIGNAL
INTERNAL
t
KILL, ON BLANKING
WDE
KILL
EN
t
8
DON'T CARE
7
), the KILL
t
9
9
t
, KILL is
KILL, ON BLANKING
2952 F12
t
< t
10
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 t
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 t
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 t
again. Finally, the third 500ms timer which starts at t
expires without any further extension at t
EN pin to go low, shutting down the DC/DC converter.
KILL, OFF WAIT
ON/OFF SIGNAL
EXTENDED HOUSE KEEPING TIME
INTERNAL
KILL
EN
t
< t
11
KILL, OFF WAIT
Figure 11. Aborted Power-On Sequence
t
12
t
KILL, OFF WAIT
12
DON'T CARE
, causing the 500ms timer to reset
t
13
t
EN, LOCKOUT
DON'T CARE
10
, the internal ON/OFF signal
t
KILL, ON BLANKING
2952 F13
11
, the LTC2952 resets
LTC2952
t
7
13
t
EN, LOCKOUT
causing the
21
2952 F11
2952fa
12