LTC4220 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC4220 Datasheet PDF : 36 Pages
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LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
APPLICATIONS INFORMATION
1
VTMRH
TIMER
2
5.8μA
" t*DRN
GATE
1
VTMRH
TIMER
GATE
CB TIMES OUT
2
" t*DRN
CB TIMES OUT
1
VTMRH
TIMER
2
34
5.8μA
" t*DRN
" t*DRN
GATE
SS
SENSE
VACL
VCB
SS
SENSE
VACL
VCB
SS
SENSE
VACL
VCB
VOUT
DRAIN
VOUT
DRAIN
VDRNCL
VOUT
DRAIN
VDRNCL
PWRGD
PWRGD
PWRGD
CB FAULT
(14a) Momentary Circuit-Breaker Fault
CB FAULT
(14b) Circuit-Breaker Time Out
CB FAULT
CB FAULT
425212 F14
(14c) Multiple Circuit-Breaker Fault
Figure 14. Circuit-Breaker Timing Behavior (All Waveforms Are Referenced to VEE)
the VTMRH threshold, TIMER is discharged by 5.8μA. In
Figure 14b, when TIMER exceeds VTMRH, GATE pulls down
immediately and the LTC4252 shuts down. In Figure 14c,
multiple momentary faults cause the TIMER capacitor to
integrate and reach VTMRH. GATE pull down follows and
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 VUVLO with a switch. Reset is also accomplished by
pulling the VIN pin momentarily below (VLKO – VLKH). A
third reset method involves pulling the TIMER pin below
VTMRL as shown in Figure 15. An initial timing cycle is
skipped if TIMER is used for reset. An initial timing cycle
is generated if reset by the UV pin or the VIN pin.
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
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 VTMRH, GATE pulls down
immediately and the LTC4252 shuts down. TIMER starts
a shutdown cooling cycle by discharging TIMER with
5.8μA to the VTMRL threshold. TIMER then charges with
5.8μA to the VTMRH threshold. There are four 5.8μA
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.
425212fd
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