LT4356-3 Linear Technology Corporation, LT4356-3 Datasheet - Page 12

• Manufacturer Part Number: LT4356-3
• Description: Surge Stopper With Fault Latchoff
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT4356-3
Fault Timer Current
The timer current starts at around 2μA with 0.5V or less
of V
ing an overvoltage fault (Figure 1). During an overcurrent
fault, it starts at 4μA with 0.5V or less of V
to 260μA with 80V across the MOSFET (Figure 2). This
arrangement allows the pass transistor to turn off faster
during an overcurrent event, since more power is dissipated
during this condition. Refer to the Typical Performance
Characteristics section for the timer current at different
V
12
DS
DS
in both overvoltage and overcurrent events.
, increasing linearly to 50μA with 75V of V
1.35
1.25
0.50
1.35
1.25
0.50
V
V
TMR(V)
TMR(V)
TOTAL FAULT TIMER = t
TOTAL FAULT TIMER = t
= 2.88ms/μF
= 15ms/μF
t
t
FLT
FLT
(I
TMR
V
Figure 1. Overvoltage Fault Timer Current
Figure 2. Overcurrent Fault Timer Current
DS
DS
(I
= 260μA)
= 80V
TMR
V
but increases
t
= 0.38ms/μF
DS
= 20ms/μF
t
WARNING
t
WARNING
FLT
t
= 50μA)
FLT
= 75V
FLT
= 21.43ms/μF
FLT
= 93.75ms/μF
DS
+ t
I
+ t
TMR
WARNING
WARNING
dur-
= 5μA
(I
TMR
V
When the voltage at the TMR pin, V
threshold, the FLT pin pulls low to indicate the detection
of a fault condition and provide warning to the load of
the impending power loss. In the case of an overvoltage
fault, the timer current then switches to a fi xed 5μA. The
interval between FLT asserting low and the MOSFET turn-
ing off is given by:
(I
DS
V
TMR
DS
= 35μA)
= 10V
t
= 10V
WARNING
= 8μA)
= 2.86ms/μF
t
WARNING
= 20ms/μF
t
WARNING
=
C
I
TMR
TMR
= 5μA
5μA
• 100mV
43563 F02
43563 F01
TIME
TIME
TMR
, reaches the 1.25V
43563f