LTC4252-2 Linear Technology, LTC4252-2 Datasheet - Page 26

• Manufacturer Part Number: LTC4252-2
• Description: Negative Voltage Hot Swap Controllers
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
V
14b, when TIMER exceeds V
immediately and the LTC4252 shuts down. In Figure 14c,
multiple momentary faults cause the TIMER capacitor to
integrate and reach V
the LTC4252 shuts down. During shutdown, the LTC4252-1
latches TIMER high with a 5.8µA pull-up current source;
the LTC4252-2 activates a shutdown cooling cycle.
Resetting a Fault Latch (LTC4252-1)
The latched circuit breaker fault of LTC4252-1 benefits
from long cooling time. It is reset by pulling the UV pin
below V
pulling the V
third reset method involves pulling the TIMER pin below
V
skipped if TIMER is used for reset. An initial timing cycle
is generated if reset by the UV pin or the V
The duration of the TIMER reset pulse should be smaller
than the time taken to reach 0.2V at SS pin. With a single
26
TMRH
TMRL
(14a) Momentary Circuit-Breaker Fault
threshold, TIMER is discharged by 5.8µA. In Figure
as shown in Figure 15. An initial timing cycle is
UVLO
PWRGD
SENSE
TIMER
DRAIN
GATE
V
OUT
SS
V
IN
with a switch. Reset is also accomplished by
TMRH
pin momentarily below (V
CB FAULT
1
U
2
TMRH
Figure 14. Circuit-Breaker Timing Behavior (All Waveforms are Referenced to V
230µA + 8 • I
V
V
ACL
CB
U
. GATE pull down follows and
5.8µA
DRN
TMRH
W
, GATE pulls down
LKO
IN
pin.
(14b) Circuit-Breaker Time Out
– V
U
PWRGD
TIMER
SENSE
DRAIN
LKH
GATE
V
OUT
SS
V
TMRH
). A
1
CB FAULT
V
DRNCL
pole mechanical pushbutton switch, this may not be
feasible. A double pole, single throw pushbutton switch
removes this restriction by connecting the second switch
to the SS pin. With this method, both the SS and TIMER
pins are released at the same time (see Figure 24).
Shutdown Cooling Cycle (LTC4252-2)
Figure 16 shows the timer behavior of the LTC4252-2. At
time point 2, TIMER exceeds V
immediately and the LTC4252 shuts down. TIMER starts
a shutdown cooling cycle by discharging TIMER with
5.8µA to the V
5.8µA to the V
discharge phases and three 5.8µA charge phases in this
shutdown cooling cycle spanning time points 2 and 3. At
time point 3, the LTC4252 automatic retry occurs with a
start-up cycle. Good thermal management techniques are
highly recommended; power and thermal dissipation must
be carefully evaluated when implementing the automatic
retry scheme.
CB TIMES OUT
230µA + 8 • I
2
V
V
ACL
CB
DRN
TMRL
TMRH
(14c) Multiple Circuit-Breaker Fault
PWRGD
SENSE
TIMER
DRAIN
threshold. TIMER then charges with
GATE
V
OUT
SS
threshold. There are four 5.8µA
V
TMRH
CB FAULT
1
2
EE
TMRH
5.8µA
230µA + 8 • I
)
V
DRNCL
CB FAULT
3
4252-1/2 F14
, GATE pulls down
CB TIMES OUT
4
DRN
230µA + 8 • I
V
V
ACL
CB
DRN
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