LT4356-3 Linear Technology Corporation, LT4356-3 Datasheet - Page 17

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

First, calculate the resistive divider value to limit V
16V during an overvoltage event:
Set the current through R1 and R2 during the overvoltage
condition to 250μA.
Choose 4.99kΩ for R2.
The closest standard value for R1 is 59kΩ.
Next calculate the sense resistor, R
C
The closest standard value for C
APPLICATIONS INFORMATION
TMR
R2 =
R1 =
R
C
V
REG
SNS
TMR
is then chosen for 1ms of early warning time:
=
(
250μA
=
1.25V
=
16V – 1.25V
1.25V • R1 + R2
50mV
1ms • 5μA
I
LIM
100mV
1.25V
= 5kΩ
R2
(
=
50mV
)
5A
= 50nF
• R2
)
= 10mΩ
= 16V
= 58.88kΩ
TMR
SNS
is 47nF .
, value:
OUT
to
Finally, calculate R4 and R5 for the 6V low battery threshold
detection:
Choose 100kΩ for R5.
Select 383kΩ for R4.
The pass transistor, Q1, should be chosen to withstand
the output short condition with V
The total overcurrent fault time is:
The power dissipation on Q1 equals to:
These conditions are well within the Safe Operating Area
of IRLR2908.
R4 =
P =
6V =
t
OC
=
14V • 50mV
1.25V • R4 + R5
(
6V – 1.25V
47nF • 0.85V
10mΩ
45.5μA
1.25V
R5
(
= 70W
)
• R5
= 0.878ms
)
= 380kΩ
CC
= 14V.
LT4356-3
17
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