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| 型号： | MAX8790ETP+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 18/24页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR WHITE BCKLGT 20-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 拓扑： | PWM，升压（升压） |
| 输出数： | 6 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 1MHz |
| 电源电压： | 4.5 V ~ 5.5 V，5.5 V ~ 26 V |
| 输出电压： | 5V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WFQFN 裸露焊盘 |
| 供应商设备封装： | 20-TQFN-EP |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 85°C |
| 产品目录页面： | 1424 (CN2011-ZH PDF) |
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
where 51mV is a scale factor based on slope compen-
sation, and R S is the current-sense resistor. To deter-
mine the minimum inductor value, the R S can be
temporarily calculated using the following equation:
Considering the typical operating circuit, the maximum
load current (I OUT(MAX) ) is 120mA with a 28.72V output
and a minimal input voltage of 7V. Choosing a DCM
operating mode and estimating efficiency of 90% at this
L DCM ( MAX ) = ? 1 ?
?×
R S _ TMP =
100 mV
,
1 . 2 × I IN ( DCMAX )
operating point:
?
?
7 V ?
28 . 72 V + 0 . 4 V ?
where 100mV is the current-limit sense voltage.
The minimum inductor value should be recalculated
( 7 V ) 2 × 0 . 9
2 × 0 . 825 MHz × 28 . 72 V × 120 mA
= 5 . 8 μ H
after the R S is determined (see the Sense-Resistor
Selection section).
Choose an available inductor value from an appropriate
An inductance less than L DCM(MAX) is required, so a
4.7μH inductor is chosen. The peak inductor current at
minimum input voltage is calculated as follows:
inductor family. Calculate the maximum DC input cur-
rent at the minimum input voltage V IN(MIN), using con-
servation of energy and the expected efficiency at that
operating point ( η MIN ) taken from an appropriate curve
I PEAK =
120mA × 2 × 28.72V × ( 28.72V + 0.4V ? 7V )
4 . 7 μ H × 0 . 675 MHz × 0 . 9 × ( 28 . 72 V + 0 . 4 V )
= 1 . 35 A
in the Typical Operating Characteristics:
Sense-Resistor Selection
,
I IN ( DCMAX ) =
I OUT(MAX ) × V OUT
V IN ( MIN ) × η MIN
The detected signal is fed into the step-up converter
control compensation loop through the CS pin.
The MAX8790’s current-mode step-up converter senses
V IN ( MIN ) × ( V OUT ( MAX ) ? V IN ( MIN ) )
L × V OUT ( MAX ) × f OSC
Calculate the ripple current at that operating point and
the peak current required for the inductor:
I RIPPLE =
the switch current from CS to GND with an external
resistor, R S . The current-limit sense voltage is a fixed
100mV. The required resistance is calculated based
upon the peak inductor current at the end of the switch
on-time:
I PEAK = I IN ( DCMAX ) + RIPPLE
,
I
2
R S <
V CS _ EC + 25.6mV × ( 0.75 ? D MAX )
I PEAK
V OUT ( MAX ) + V DIODE ?
D MAX =
When DCM operating mode is chosen to minimize the
inductor value, the calculations are different from that in
the above CCM mode. The maximum inductor value for
DCM mode is calculated by the following equation:
? V IN ( MIN ) ?
L DCM ( MAX ) = ? 1 ? ?×
?
V IN ( MIN ) 2 × η
2 × f OSC ( MAX ) × V OUT ( MAX ) × I OUT ( MAX )
where 25.6mV is a scale factor from slope compensa-
tion, V CS_EC is the current-sense voltage listed in the
Electrical Characteristics table (85mV), and the D MAX is
the maximum duty cycle at minimum input voltage and
maximum output voltage. In DCM operating mode, it is
calculated by the following equation:
L × I LIM × f OSC
V IN ( MIN )
For the typical operating circuit as Figure 1:
The peak inductor current in DCM mode is calculated
using the following equation:
D MAX =
4.7 μ H × 1.35A × 0.75MHz
7 V
= 0 . 68
I PEAK =
I OUT(max) × 2 × V OUT(MAX ) × ( V OUT(MAX ) + V DIODE ? V IN(MIN) )
L × f OSC ( MIN ) × η × ( V OUT ( MAX ) + V DIODE )
R S <
85mV + 25.6mV × ( 0.75 ? 0.68 )
1 . 35 A
= 64 m Ω
The inductor’s saturation current rating should exceed
I PEAK and the inductor ’s DC current rating should
exceed I IN(DC,MAX) . For good efficiency, choose an
inductor with less than 0.1 Ω series resistance.
Again, R S is calculated as a maximum, so a 56m Ω cur-
rent-sense resistor is chosen.
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8790ETP+ | 功能描述:LED照明驱动器 Six-String White LED Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX8790ETP+T | 功能描述:LED照明驱动器 Six-String White LED Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX8790EVKIT+ | 功能描述:LED 照明开发工具 RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| MAX8791AGTA+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX8791AGTA+T | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
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