LT4356CS-3 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT4356CS-3' PDF : 24 Pages View PDF
LT4356-3
APPLICATIONS INFORMATION
First, calculate the resistive divider value to limit VOUT to
16V during an overvoltage event:
VREG
=
1.25V
•
(R1
R2
+
R2)
=
16V
Set the current through R1 and R2 during the overvoltage
condition to 250µA.
R2 =
1.25V
250µA
= 5kΩ
Choose 4.99kΩ for R2.
R1
=
(16V – 1.25V)
1.25V
• R2
=
58.88kΩ
The closest standard value for R1 is 59kΩ.
Next calculate the sense resistor, RSNS, value:
RSNS
=
50mV
ILIM
=
50mV
5A
= 10mΩ
CTMR is then chosen for 1ms of early warning time:
CTMR
=
1ms • 5µA
100mV
= 50nF
The closest standard value for CTMR is 47nF.
Finally, calculate R4 and R5 for the 6V low battery thresh-
old detection:
6V = 1.25V • (R4 + R5)
R5
Choose 100kΩ for R5.
R4
=
(6V
– 1.25V)
1.25V
• R5
=
380kΩ
Select 383kΩ for R4.
The pass transistor, Q1, should be chosen to withstand
the output short condition with VCC = 14V.
The total overcurrent fault time is:
tOC
=
47nF • 0.85V
45.5µA
= 0.878ms
The power dissipation on Q1 equals to:
P = 14V • 50mV = 70W
10mΩ
These conditions are well within the Safe Operating Area
of IRLR2908.
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