LT4250L/LT4250H

10

4250lhfa

Figure 8. Voltage Step on Input Supply Waveforms

APPLICATIONS INFORMATION

Figure 9. Circuit for Input Steps with Small C2 (<10nF)

Figure 10. Automatic Restart After Current Fault

DRAIN

20V/DIV

5A/DIV

500μs/DIV

4250 08

LT4250H

PWRGD

SENSE

C1

150nF

25V

C3

0.1μF

100V

C4

22μF

100V

Q1

IRF530

R2

10Ω

5%

R3

1k

5%

C2

3.3nF

100V

R4

549k

1%

R5

6.49k

1%

R6

10k

1%

R1

0.02Ω

5%

4

3

2

–48V RTN

–48V

OV

UV

56

8

1

GATE

DRAIN

4250 F09

+

7

–48V RTN

(SHORT PIN)

*

* DIODES INC. SMAT70A

R7

220Ω

5%

4

3

2

1

D1

BAT85

LT4250L

PWRGD

SENSE

C1

470nF

25V

C4

1μF

100V

C3

100μF

100V

Q1

IRF530

R2

10Ω

5%

R8

510k

5%

R3

1k, 5%

C2

15nF

100V

R4

549k

1%

R7

1M

5%

R5

16.5k

1%

R9

10k

1%

R6

549k

1%

Q3

ZVN3310

Q2

2N2222

D1

1N4148

R1

0.02Ω

5%

4

3

2

OV

–48V

UV

56

8

7

1

GATE

DRAIN

4250 F10a

3

2

+

–48V RTN

–48V RTN

(SHORT PIN)

*

* DIODES INC. SMAT70A

4

3

2

1

NODE 2

50V/DIV

GATE

2V/DIV

1s/DIV

4250 F10

A circuit that automatically resets the circuit breaker after

a current fault is shown in Figure 10. Transistors Q2 and

Q3 along with R7, R8, C4 and D1 form a programmable

one-shot circuit. Before a short occurs, the GATE pin is

Resistor R8 turns off Q2. When a short occurs, the GATE

pin is pulled low and Q3 turns off. Node 2 starts to charge

C4 and Q2 turns on, pulling the UV pin low and resetting

the circuit breaker. As soon as C4 is fully charged, R8 turns

off Q2, UV goes high and the GATE starts to ramp up. Q3

cycle is set to 10% to prevent Q1 from overheating.