LTC1642 Linear Technology, LTC1642 Datasheet - Page 7

• Manufacturer Part Number: LTC1642
• Description: Hot Swap Controller
• Manufacturer: Linear Technology

2.5A
APPLICATIO S I FOR ATIO
Automatic Restart After a Current Fault
The LTC1642 will automatically attempt to restart itself
after the circuit breaker opens if the FAULT output is tied
to the ON pin. The circuit is shown in Figure 5, and the
waveforms during a load short in Figure 6.
During a continuous current limit such as a load short, the
N-channel pass transistor’s duty cycle is equal to the
circuit breaker timer period, divided by the sum of the
circuit breaker and system timer periods. If FAULT is tied
to ON then open drain logic should be used to drive the
12V
0.1 F
V
IN
ALL RESISTORS 5% UNLESS NOTED
SHORT-CIRCUIT DUTY CYCLE =
C7
R5
0.33 F
C4
R1
Figure 5. Automatic Restart Circuit
4
6
9
2
ON
FAULT
OV
BRK TMR
RST TMR
V
CC
16
U
LTC1642
3
0.010
R2
C1
0.33 F
C4 + 10 • C1
SENSE
CRWBR
C4
U
GATE
GND
15
8
14
1
= 9%
FDR9410A
2.5A
THRESHOLD = 10.7V
12V
V
ALL RESISTORS 5% UNLESS NOTED
IN
Q1
UNDERVOLTAGE
W
R3
100
R4
330
C5
C2
0.047 F
Figure 7. Setting a Higher Undervoltage Lockout
2N2222
LOCKOUT
+
C7
0.1 F
Q2
C
LOAD
U
R1
464k
1%
R5
60.4k
1%
4
Q3
MCR
12DC
1642 F05
V
ON
RST TMR
OUT
V
CC
16
LTC1642
3
0.010
R2
C1
0.33 F
node. The external pull-up resistor at the ON pin may be
omitted because FAULT provides a weak pull-up.
Undervoltage Lockout
An internal undervoltage lockout circuit holds the charge
pump off until V
it turns off the charge pump and clears overvoltage and
current limit faults.
For higher lockout thresholds tie the ON pin to a resistor
divider driven from V
circuit keeps the charge pump off until V
(1+R1/R5)•1.34V, and also turns it off if V
(1+R1/R5)•1.23V.
SENSE
GATE
GND
15
8
BRK TMR
ON/FAULT
RST TMR
Figure 6. Automatic Retry Following a Load Short
14
FDR9410A
1
Q1
GATE
V
OUT
R3
100
R4
330
C2
0.047 F
CC
2
+
exceeds 2.73V. If V
1642 F07
C
LOAD
3
V
CC
OUT
4
, as shown in Figure 7. This
5
CC
6
LTC1642
falls below 2.5V,
CC
1642 F06
1.23V
1.23V
CC
falls below
exceeds
7