ltc4221 Linear Technology Corporation, ltc4221 Datasheet - Page 17

• Manufacturer Part Number: ltc4221
• Description: Dual Hot Swap Controller/power Sequencer With Dual Speed, Dual Level Fault Protection
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
duty cycle of more than 1.8% will eventually trip the circuit
breaker. Figure 8 shows the circuit breaker response time
in seconds normalized to 1μF. The asymmetric charging and
discharging of FILTER is a fair gauge of MOSFET heating.
C
FILTER
t
0.01
SENSE n
0.1
FILTER
Figure 8. Circuit Breaker Filter Response
for Intermittent Overload
TIMER
GATE n
FAULT
( )
V
1
OUT n
μ
ON n
0
F
10 20 30 40 50 60 70 80 90 100
=
RESET
0.851V
OVERLOAD DUTY CYCLE, D (%)
(
U
105
1
μ
C
A D
FILTER
U
1 24
•
.
t
(μF)
)
V
– .
1.9μA
=
1 8
105 • D – 1.8
W
INITIAL TIMING
1.24V
μ
Figure 9. Fast Comparator Trip Timing Waveforms
A
4221 F08
V
U
TMR(H)
V
TMR(L)
(2)
2
3
ELECTRONIC CIRCUIT BREAKER ARMED
START-UP
20μA
CHANNEL
9.5μA
The fast comparators trip the circuit breaker to protect
against fast load overcurrents if V
V
comparator is fixed at 1μs nominal. The timing diagram in
Figure 9 illustrates the operation of the LTC4221 when the
load current conditions cause V
ceed 100mV for more than 1μs between time points 7 and
8. Figure 9 also illustrates when the LTC4221’s electronic
circuit breaker is armed. After the initial timing cycle, it is
armed at time point 3. Arming the circuit breaker at time
point 3 ensures that the system is protected against an over-
current condition during the channel start-up cycle. At time
point 4, the slow comparators are armed when the internal
control loop is disengaged.
Autoretry After a Fault
Once the LTC4221 circuit breaker is tripped, FAULT is
latched low and both GATE pins are pulled to ground. To
clear the internal FAULT latch and to restart the LTC4221,
its ON1 pin must be pulsed below its reset threshold
(V
SENSE(FC)
ON(RESET)
SLOW COMPARATORS ARMED
4 5
20μA
V
V
NORMAL
SENSE(SC)
SENSE(FC)
(100mV) for 1μs. The response time of each fast
= 0.4V) for at least 15μs.
105μA
6 7
8
V
FILTER(TH)
FAULT
1.8μA
RSENSE
RSENSE
0.4V
of channel 1 to ex-
9
RESET
LTC4221
4221 F09
is greater than
17
4221fa