参数资料
型号: LM3423MH/NOPB
厂商: National Semiconductor
文件页数: 31/67页
文件大小: 0K
描述: IC LED DRVR HP CONS CURR 20TSSOP
产品培训模块: PowerWise® Products and Technology
LED Design Solutions
特色产品: LM3421 and LM3423 Controllers
标准包装: 73
系列: PowerWise®
恒定电流:
拓扑: PWM,SEPIC,降压(降压),升压(升压)
输出数: 1
内部驱动器:
类型 - 主要: 车载
类型 - 次要: 高亮度 LED(HBLED)
频率: 2MHz
电源电压: 4.5 V ~ 75 V
输出电压: 3 V ~ 72 V
安装类型: 表面贴装
封装/外壳: 20-TSSOP(0.173",4.40mm 宽)裸露焊盘
供应商设备封装: 20-TSSOP-EP
包装: 管件
工作温度: -40°C ~ 125°C
产品目录页面: 1284 (CN2011-ZH PDF)
其它名称: *LM3423MH/NOPB
LM3423MH

SNVS574E – JULY 2008 – REVISED MAY 2013
Design Guide
Refer to the Basic Topology Schematics section.
SPECIFICATIONS
Number of series LEDs: N
Single LED forward voltage: V LED
Single LED dynamic resistance: r LED
Nominal input voltage: V IN
Input voltage range: V IN-MAX , V IN-MIN
Switching frequency: f SW
Current sense voltage: V SNS
Average LED current: I LED
Inductor current ripple: Δ i L-PP
LED current ripple: Δ i LED-PP
Peak current limit: I LIM
Input voltage ripple: Δ v IN-PP
Output OVLO characteristics: V TURN-OFF , V HYSO
Input UVLO characteristics: V TURN-ON , V HYS
1. OPERATING POINT
Given the number of series LEDs (N), the forward voltage (V LED ) and dynamic resistance (r LED ) for a single LED,
solve for the nominal output voltage (V O ) and the nominal LED string dynamic resistance (r D ):
V O = N x V LED
r D = N x r LED
Solve for the ideal nominal duty cycle (D):
Buck
(34)
(35)
D=
Boost
D=
V O
V IN
V O - V IN
V O
(36)
(37)
Buck-boost
D=
V O
V O + V IN
(38)
Using the same equations, find the minimum duty cycle (D MIN ) using maximum input voltage (V IN-MAX ) and the
maximum duty cycle (D MAX ) using the minimum input voltage (V IN-MIN ). Also, remember that D' = 1 - D.
2. SWITCHING FREQUENCY
Set the switching frequency (f SW ) by assuming a C T value of 1 nF and solving for R T :
Copyright ? 2008–2013, Texas Instruments Incorporated
31
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
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