Datasheet

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
V
EE
AND
DRAIN
20V/DIV
I
D
(Q1)
5A/DIV
500μs/DIV
4250 08
V
EE
V
DD
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%
43
21
D1
BAT85
V
EE
V
DD
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
43
21
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
pulled high and Q3 is turned on, pulling node 2 to V
EE
.
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
turns back on and quickly pulls node 2 back to V
EE
. Diode
D1 clamps node 3 one diode drop below V
EE
. The duty
cycle is set to 10% to prevent Q1 from overheating.