7

LTC1642

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

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

it turns off the charge pump and clears overvoltage and

current limit faults.

For higher lockout thresholds tie the ON pin to a resistor

(1+R1/R5)•1.23V.

GATE

14

SENSE

15

ON

4

16

R2

0.010

Ω

Q1

FDR9410A

GND

LTC1642

8

RST TMR

3

R1

464k

1%

R5

60.4k

1%

12V

2.5A

1642 F07

R3

100

Ω

R4

330

Ω

C2

0.047

µF

+

C7

0.1

µF

C1

0.33

µF

ALL RESISTORS

±5% UNLESS NOTED

UNDERVOLTAGE

LOCKOUT

THRESHOLD = 10.7V

Figure 7. Setting a Higher Undervoltage Lockout

6

5

4

3

2

1

BRK TMR

1.23V

1.23V

1642 F06

GATE

RST TMR

ON/FAULT

GATE

ON

14

SENSE

15

CRWBR

1

4

FAULT

6

OV

BRK TMR

2

9

16

R2

0.010

Ω

Q1

FDR9410A

GND

LTC1642

8

RST TMR

3

R5

1642 F05

R3

100

Ω

R4

330

Ω

C2

0.047

µF

+

C7

0.1

µF

C1

0.33

µF

C4

0.33

µF

ALL RESISTORS

±5% UNLESS NOTED

Q2

2N2222

Q3

MCR

12DC

C5

12V

2.5A

R1

C4

C4 + 10 • C1

SHORT-CIRCUIT DUTY CYCLE =

= 9%

Figure 5. Automatic Restart Circuit

Figure 6. Automatic Retry Following a Load Short