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| 型号： | MAX8790ETP+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 20/24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
Input Capacitor Selection
The input capacitor (C IN ) filters the current peaks drawn
from the input supply and reduces noise injection into
the IC. A 10μF ceramic capacitor is used in the typical
operating circuit (Figure 1) because of the high source
impedance seen in typical lab setups. Actual applica-
tions usually have much lower source impe-dance since
the step-up regulator often runs directly from the output
of another regulated supply. In some applications, C IN
can be reduced below the values used in the typical
operating circuit. Ensure a low noise supply at IN by
using adequate C IN . Alternatively, greater voltage varia-
tion can be tolerated on C IN if IN is decoupled from C IN
using an RC lowpass filter.
Select C IN ’s RMS ripple current rating to ensure that its
thermal rise is less than approximately 10°C:
voltage drop is lower than the maximum input voltage,
the voltage drop across the current-sense inputs (FB_)
increases and causes excess heating in the IC.
Between 8 and 12 LEDs in series is ideal for input volt-
ages up to 20V.
Applications Information
LED V FB_ Variation
The MAX8790 has accurate (±1.5%) matching for each
current source. However, the forward voltage of each
white LED can vary up to ±5% from part to part. The
accumulated voltage difference in each string equates
to additional power loss within the IC. For the best effi-
ciency, the voltage difference between strings should
be minimized. The difference between lowest voltage
string and highest voltage string should be less than
I RMS =
dI L
2 × 3
4.5V. Otherwise, the internal LED short-circuit protection
shuts the part off.
Choosing the Appropriate Dimming Mode
LED Selection and Bias
The series/parallel configuration of the LED load and the
full-scale bias current have a significant effect on regu-
lator performance. LED characteristics vary significantly
from manufacturer to manufacturer. Consult the respec-
tive LED data sheets to determine the range of output
voltages for a given brightness and LED current. In ge-
neral, brightness increases as a function of bias current.
This suggests that the number of LEDs could be
decreased if higher bias current is chosen; however,
high current increases LED temperature and reduces
operating life. Improvements in LED technology are
resulting in devices with lower forward voltage while
increasing the bias current and light output.
LED manufacturers specify LED color at a given LED
current. With lower LED current, the color of the emitted
light tends to shift toward the blue range of the spec-
trum. A blue bias is often acceptable for business appli-
cations but not for high-image-quality applications such
as DVD players. Direct DPWM dimming is a viable solu-
tion for reducing power dissipation while maintaining
LED color integrity. Careful attention should be paid to
switching noise to avoid other display quality problems.
Using fewer LEDs in a string improves step-up
converter efficiency, and lowers breakdown voltage
requirements of the external MOSFET and diode. The
minimum number of LEDs in series should always be
greater than the maximum input voltage. If the diode
Analog dimming mode allows lower peak LED current
and results in higher converter efficiency and lower
noise compared to direct DPWM mode. Unfortunately,
the LED color spectrum can shift as a function of DC
current so DPWM mode is often used to achieve more
consistent display characteristics. (See the LED manu-
facturer ’s data sheet to determine the extent of the
color shift.) When the MAX8790 is configured with an
FSET resistor and CPLL capacitor, the ENA signal can
toggle between modes on the fly. Care should be exer-
cised when switching between modes to prevent the
current from becoming unstable during the PLL lock-in
time. To avoid such problems, force the controller into
DPWM mode between transitions.
LCD Panel Capacitance
Some LCD panels include a capacitor in parallel with
LED string to improve ESD immunity. Because of the
10μA pullup current source in each FB_ input for string
detection, the MAX8790 can start up with less than
470pF capacitance on each FB_ pin. If the string
capacitance C LED is greater than 470pF, a bank of
pullup resistors to V IN should be added to prevent
startup problems (see Figure 6). A delay of 3 x 1M Ω x
C LED should be added after V IN was settled before
enabling the MAX8790 to ensure the FB_ voltage
exceeds the 3V internal threshold. A similar delay
should be added after the part is shut down to ensure
proper restart.
20
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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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