LTC2952CF datasheet(21/30 Pages) LINER

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LTC2952

2952fa

Figure 11. Aborted Power-On Sequence

2952 F11

KILL

INTERNAL

ON/OFF SIGNAL

tKILL, ON BLANKING

DON'T CARE

tEN, LOCKOUT

2952 F12

KILL

INTERNAL

ON/OFF SIGNAL

tKILL, ON BLANKING

DON'T CARE

Figure 12. KILL Initiated Shutdown

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.

APPLICATIONS INFORMATION

Figure 13. Power-On/Power-Off Sequence with Extended Shutdown/Housekeeping Wait Time

2952 F13

KILL

INTERNAL

ON/OFF SIGNAL

tKILL, ON BLANKING < tKILL, OFF WAIT

WDE

t10

t11

t12

t13

DON'T CARE

EXTENDED HOUSE KEEPING TIME

tKILL, OFF WAIT

tEN, LOCKOUT

< tKILL, OFF WAIT

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.

LTC2952CF Datasheet(PDF) 21 Page - Linear Technology

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