LT1640 Linear Technology, LT1640 Datasheet - Page 9

• Manufacturer Part Number: LT1640
• Description: Negative Voltage Hot Swap Controller
• Manufacturer: Linear Technology

APPLICATIONS
Under some conditions, a short circuit at the output can
cause the input supply to dip below the UV threshold,
resetting the circuit breaker immediately.
The LT1640 then cycles on and off repeatedly until the
short is removed. This can be minimized by adding a
deglitching delay to the UV pin with a capacitor from UV to
V
resistors at UV, allowing the input supply to recover before
the UV pin resets the circuit breaker.
A circuit that automatically resets the circuit breaker after
a current fault is shown in Figure 9.
Transistors Q2 and Q3 along with R7, R8, C4 and D1 form
a programmable one-shot circuit. Before a short occurs,
EE
. This capacitor forms an RC time constant with the
– 48V
GND
U
1N4148
D1
INFORMATION
2N2222
U
Q2
100V
1 F
C4
5%
1M
R7
3
R8
510k
5%
ZVN3310
W
2
Figure 9. Automatic Restart After Current Fault
Q3
9.09k
562k
10k
1%
1%
1%
U
R4
R5
R6
3
2
UV
OV
V
EE
4
0.02
5%
R1
SENSE
the GATE pin is pulled high and Q3 is turned on, pulling
node 2 to V
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
below V
overheating.
Undervoltage and Overvoltage Detection
The UV (Pin 3) and OV (Pin 2) pins can be used to detect
undervoltage and overvoltage conditions at the power
5
C1
0.033 F
24V
LT1640L
EE
V
. The duty cycle is set to 10% to prevent Q1 from
DD
IRF530
GATE
8
EE
Q1
EE
6
R2
10
5%
. Diode D1 clamps node 3 one diode drop
. Resistor R8 turns off Q2. When a short
10k
5%
R3
1640 F09b
3.3nF
100V
C2
PWRGD
DRAIN
LT1640L/LT1640H
7
1
+
1640 F09a
C3
100 F
100V
9