参数资料
型号: LM3423MHBKBSTEV/NOPB
厂商: National Semiconductor
文件页数: 41/67页
文件大小: 0K
描述: BOARD EVAL BUCK BOOST LM3423
标准包装: 1
系列: PowerWise®
电流 - 输出 / 通道: 1A
输出及类型: 1,非隔离
输出电压: 35V
特点: 可调光
输入电压: 4.5 ~ 35 V
已供物品:
已用 IC / 零件: LM3423
其它名称: LM3423MHBKBSTEV
2. SWITCHING FREQUENCY
Assume C T = 1 nF and solve for R T :
SNVS574E – JULY 2008 – REVISED MAY 2013
R T =
25
f SW x C T
=
25
500 kHz x 1 nF
= 50 k :
(101)
The closest standard resistor is 49.9 k ? therefore f SW is:
f SW =
25
R T x C T
=
25
49.9 k : x 1 nF
= 501 kHz
(102)
The chosen component from step 2 is:
C T = 1 nF
R T = 49.9 k :
3. AVERAGE LED CURRENT
Solve for R SNS :
(103)
R SNS = SNS =
V
I LED
100 mV
1A
= 0 . 1 :
(104)
Assume R CSH = 12.4 k ? and solve for R HSP :
I LED x R CSH x R SNS 1 A x 12.4 k : x 0.1 :
=
R HSP =
1.24V 1.24V
= 1 . 0 k :
(105)
The closest standard resistor for R SNS is actually 0.1 ? and for R HSP is actually 1 k ? therefore I LED is:
I LED =
1.24V x R HSP
R SNS x R CSH
=
1.24V x 1. 0 k :
0 . 1 : x 12 . 4 k :
= 1 . 0 A
(106)
The chosen components from step 3 are:
R S NS = 0.1 :
R CSH = 1 2 . 4 k :
R HSP = R HSN = 1 k :
4. INDUCTOR RIPPLE CURRENT
Solve for L1:
(107)
L 1 =
V IN x D
' i L - PP x f SW
=
2 4 V x 0 . 467
700 mA x 5 01 kHz
= 32 P H
(108)
The closest standard inductor is 33 μH therefore Δ i L-PP is:
' i L - PP =
V IN x D
L 1 x f SW
=
2 4 V x 0 . 467
33 P H x 5 01 kHz
= 678 mA
(109)
Determine minimum allowable RMS current rating:
I L - RMS = LED x 1 +
x D c ·
§ ' i
?
x ¨ ¨ L - PP
I LED
12 ?
I
D c
1
2
?
1
§ 678 mA x 0 . 533 ·
? ? = 1 . 89 A
x ¨ ¨
I L - RMS =
1 A
0 . 533
x 1 +
1
12 ? 1 A 1
2
(110)
The chosen component from step 4 is:
Copyright ? 2008–2013, Texas Instruments Incorporated
41
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
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