User manual

R10 = =
= 14.4 k:
1 + 1.95e
-8
x f
SW
1.40e
-10
x f
SW
1 + 1.95e
-8
x 500 kHz
1.40e
-10
x 500 kHz
D
MAX
==
677.0
=
V21
V10V21 +
V
O
VV
IN-MINO
+
21V
=
21V + 70V
= 0.231
D
MIN
=
V
O
+ V
IN-MAX
V
O
533.0467.01D1'D
=
-
=
-
=
D
==
467.0
=
V21
V24V21 +
V
O
VV
INO
+
:
=
:x
=
x
=
95.1m3256rNr
LEDD
V21V5.36VNV
LEDO
=
x
=
x
=
Design Procedure www.ti.com
8 Design Procedure
8.1 Specifications
N = 6
V
LED
= 3.5V
r
LED
= 325 mΩ
V
IN
= 24V
V
IN-MIN
= 10V
V
IN-MAX
= 70V
f
SW
= 500 kHz
V
SNS
= 100 mV
I
LED
= 1A
Δi
L-PP
= 700 mA
Δi
LED-PP
= 12 mA
Δv
IN-PP
= 100 mV
I
LIM
= 6A
V
TURN-ON
= 10V
V
HYS
= 3V
V
TURN-OFF
= 50V
V
HYSO
= 10V
T
BK
= 45°C
T
END
= 125°C
t
TSU
= 40 ms
8.2 Operating Point
Solve for V
O
and r
D
:
(1)
(2)
Solve for D, D', D
MAX
, and D
MIN
:
(3)
(4)
(5)
(6)
8.3 Switching Frequency
Solve for R
T
:
(7)
8
AN-1967 LM3424 Buck-Boost Evaluation Board SNVA397A–August 2009–Revised May 2013
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