LTC1642A
U
W
U U
APPLICATIO S I FOR ATIO
Q1
FDS6630A
Automatic Restart After the Circuit Breaker Opens
R2
0.015Ω
V
IN
12V
V
OUT
The LTC1642A 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. Diode D1
blockstheweakFAULTpull-upcurrentsourcefromunbal-
ancing the R6-R5 divider.
2.5A
+
16
15
SENSE
R6
464k
1%
C
LOAD
R3
V
CC
100Ω
4
6
14
ON
FAULT
LTC1642A
GATE
R4
330Ω
D2
1N4705
18V
D1
1N4148
During a continuous current limit such as a load short,
Q1’s duty cycle is equal to the circuit breaker timer period,
divided by the sum of the circuit breaker and system timer
periods:
C2
0.047µF
R5
60.4k
1%
2
BRK TMR
R10
30k
RST TMR
3
GND
8
C4
0.33µF
C1
0.33µF
C4
Short-Circuit Duty Cycle =
C4 + 10•C1
1642a F05
ALL RESISTORS ±5% UNLESS NOTED
Figure 5. Automatic Restart Circuit
The duty cycle is 9% for the Figure 5 circuit. Waveforms
during a load short are shown in Figure 6.
Undervoltage Lockout
VGATE
20V/DIV
An internal undervoltage lockout circuit holds the charge
pump off until VCC exceeds 2.73V. If VCC falls below 2.5V,
it turns off the charge pump and clears overvoltage and
current limit faults.
VOUT
10V/DIV
VBRKTMR
1V/DIV
For higher lockout thresholds tie the ON pin to a resistor
divider driven from VCC, as shown in Figure 7. This
circuit keeps the charge pump off until VCC exceeds
(1+R6/R5) • 1.34V, and also turns it off if VCC falls below
(1+R6/R5) • 1.22V.
VRSTTMR
1V/DIV
40ms/DIV
1642a F06
Figure 6. Automatic Retry Following a Load Short
R2
Q1
0.015Ω
FDS6630A
V
IN
V
12V
OUT
2.5A
+
16
15
SENSE
C
LOAD
V
R6
464k
1%
CC
R3
100Ω
LTC1642A
UNDERVOLTAGE
LOCKOUT
THRESHOLD = 10.7V
14
4
GATE
ON
D1
1N4705
18V
R4
330Ω
R5
60.4k
1%
RST TMR
3
GND
8
C1
0.33µF
C2
0.047µF
1642a F07
ALL RESISTORS ±5% UNLESS NOTED
Figure 7. Setting a Higher Undervoltage Lockout
1642af
11
Linear [ Linear ]
