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V
TURN-ON
=
R5
1.24V x (1.43 k: + 10 k:)
1.43 k:
1.24V x (R5 + R13)
= 9.91V
V
TURN-ON
=
1.24V x R13
V
TURN-ON
- 1.24V
= 1.42 k:
R5 = =
1.24V x 10 k:
10V - 1.24V
V
HYS
=
R5
20 PA x 17.4 k: x (1.43 k: + 10 k:)
1.43 k:
V
HYS
=
+ 20 PA x R13
20 PA x R4 x (R5 + R13)
+ 20 PA x 10 k: = 2.98V
R4 =
R5 x (V
HYS
- 20 PA x R13)
20 PA x (R5 + R13)
= 17.5 k:
R4 =
1.43 k: x (3V - 20 PA x 10 k:)
20 PA x (1.43 k: + 10 k:)
D1 o 12A, 100V, DPAK
mW600mV600A1VIP
FDDD
=
x
=
x
=
A1II
LEDMAXD
==
-
V91V21V70VVV
OMAXINMAXRD
=
+
=
+
=
--
Q1 o 32A, 100V, DPAK
mW82m50A28.1RIP
2
DSON
2
RMSTT
=
:x
=
x
=
-
x
I
RMST
=
-
I
LED
D
c
=
x
A28.1
=
0.467
A1
533.0
D
=
A2.1A1
=
x
677.01-
677.0
I
MAXT-
V91V21V70VVV
OMAXINMAXT
=+=+=
--
Design Procedure www.ti.com
8.12 NFET
Determine minimum Q1 voltage rating and current rating:
(40)
(41)
A 100V NFET is chosen with a current rating of 32A due to the low R
DS-ON
= 50 mΩ. Determine I
T-RMS
and
P
T
:
(42)
(43)
The chosen component from step 11 is:
(44)
8.13 Diode
Determine minimum D1 voltage rating and current rating:
(45)
(46)
A 100V diode is chosen with a current rating of 12A and V
D
= 600 mV. Determine P
D
:
(47)
The chosen component from step 12 is:
(48)
8.14 Input UVLO
Solve for R
UV2
:
(49)
The closest standard resistor is 150 kΩ therefore V
HYS
is:
(50)
Solve for R
UV1
:
(51)
The closest standard resistor is 21 kΩ making V
TURN-ON
:
(52)
12
AN-1967 LM3424 Buck-Boost Evaluation Board SNVA397A–August 2009–Revised May 2013
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