LM3424 Datasheet, PDF (45/69 Pages) National Semiconductor (TI) – Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs

www.ti.com
LM3424, LM3424-Q1
SNVS603C – AUGUST 2009 – REVISED AUGUST 2015
Typical Applications (continued)
V_HYSO = R_OV2 x 20PA = 499 k: x 20 PA = 9.98V
Solve for R_OV1:
R_OV1 =
1.24Vx R_OV2
V_TURN-OFF- 0.62V
=
1.24V x 499 k:
40V - 0.62V
=
15.7 k:
The closest standard resistor is 15.8 kΩ making V_TURN-OFF:
( ) 1.24V x
V_TURN-OFF =
0.5 x R_OV1+ R_OV2
R_OV1
1.24V x(0.5 x15.8 k: + 499 k:)
V_TURN-OFF =
15.8 k:
= 39.8V
The chosen components from step 14 are:
R_OV1 = 15.8 k:
R_OV2 = 499 k:
(155)
(156)
(157)
(158)
8.2.2.2.15 Soft-Start
Solve for t_SU:
t_SU
=
168:
x
C_BYP
+ 36
k:
x
C_CMP
+
V_O
I_LED
x
C_O
t_SU
=
168:
x
2.2
PF
+
36
k:
x
0.33
PF
+
21V
1A
x
40
PF
t_SU = 13.1 ms
If t_SU is less than t_TSU, solve for t_SU-SS-BASE:
t_{SU- SS- BASE}
=
168:
x
C_BYP
+ 28
k:
x
C_CMP
+
V_O
I_LED
x
C_O
t _{SU SS}
BASE
=
168:
x
2.2
PF
+
28
k:
x
0.33
PF
+
21V
1A
x
40
PF
t_{SUSS BASE} = 10.5 ms
Solve for C_SS:
C_SS
( ) ₌ t_TSU - t_SU-SS-BASE
20 k:
(30
=
ms -10.5
20 k:
ms)
=
975
nF
The chosen component from step 15 is:
C_SS = 12F
(159)
(160)
(161)
(162)
QTY
1
1
2
1
4
4
1
1
PART ID
LM3424
C_BYP
C_CMP, C_NTC
C_FS
C_IN
C_O
C_OV
C_REF, C_SS
Table 1. Bill of Materials
PART VALUE
Boost controller
2.2 µF X7R 10% 16V
0.33 µF X7R 10% 25V
0.27 µF X7R 10% 25V
4.7 µF X7R 10% 100V
10 µF X7R 10% 50V
47 pF COG/NPO 5% 50V
1 µF X7R 10% 25V
MANUFACTURER
TI
MURATA
MURATA
MURATA
TDK
TDK
AVX
MURATA
PART NUMBER
LM3424MH
GRM21BR71C225KA12L
GRM21BR71E334KA01L
GRM21BR71E274KA01L
C5750X7R2A475K
C4532X7R1H106K
08055A470JAT2A
GRM21BR71E105KA01L
Copyright © 2009–2015, Texas Instruments Incorporated
Product Folder Links: LM3424 LM3424-Q1
Submit Documentation Feedback
45