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| 型号： | MAX8790ETP+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 19/24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
I OUT ( MAX ) ? V OUT ( MAX ) ? V IN ( MIN ) ?
R DS ( ON ) × L × f OSC × I PEAK 3
3 × V IN ( MIN )
0 . 1 Ω × 4 . 7 μ H × 750 kHz × 1 . 35 A 3
3 × 7 V
PD SW ( MAX ) = turn ? off PEAK OUT OSC
Output Capacitor Selection
The total output voltage ripple has two components: the
capacitive ripple caused by the charging and discharging
on the output capacitor, and the ohmic ripple due to the
capacitor’s equivalent series resistance (ESR):
V RIPPLE = V RIPPLE ( C ) + V RIPPLE ( ESR )
V RIPPLE ( C ) ≈ ? ?
C OUT ? V OUT ( MAX ) f OSC ?
and:
V RIPPLE ( ESR ) ≈ I PEAK R ESR ( COUT )
where I PEAK is the peak inductor current (see the
Inductor Selection section).
The output voltage-ripple voltage should be low
enough for the FB_ current-source regulation. The rip-
The MOSFET conduction loss or resistive loss is
caused by the MOSFET’s on-resistance (R DS(ON) ). This
power loss can be estimated as:
PD RES ( MAX ) =
For the above Si3458DV, the estimated conduction loss is:
PD RES ( MAX ) = = 0 . 04 W
The approximate maximum switching loss can be cal-
culated as:
t × I × V × f
2
For the above Si3458DV, the approximate switching
loss is:
ple voltage should be less than 200mV P-P . For ceramic
capacitors, the output-voltage ripple is typically domi-
nated by V RIPPLE(C) . The voltage rating and tempera-
ture characteristics of the output capacitor must also
PD SW ( MAX ) =
10ns × 1.35A × 28.72V × 750kHz
2
= 0 . 145 W
be considered.
External MOSFET Selection
The MAX8790 ’s step-up converter uses an external
MOSFET to enable applications with scalable output
voltage and output power. The boost switching architec-
ture is simple and ensures that the controller is never
exposed to high voltage. Only the external MOSFET,
diode, and inductor are exposed to the output voltage
plus one Schottky diode forward voltage:
V BV = N × V F _ LED + V F _ SCHOTTKY + V FB _
The MOSFET’s breakdown ratings should be higher
than V BV with sufficient margin to ensure long-term relia-
bility. A conservative rule of thumb, a minimum 30%
margin would be recommended for MOSFET break-
down voltage. The external MOSFET should have a cur-
rent rating of no less than the I PEAK derived from the
Inductor Selection section. To improve efficiency,
choose a MOSFET with low R DS(ON) . The MAX8790’s
gate-drive linear regulator can provide 10mA. Select the
external MOSFET with a total gate charge so the aver-
age current to drive the MOSFET at maximum switching
Rectifier Diode Selection
The MAX8790’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended
for most applications because of their fast recovery
time and low forward voltage. The diode should be
rated to handle the output voltage and the peak switch
current. Make sure that the diode’s peak current rating
is at least I PEAK calculated in the Inductor Selection
section and that its breakdown voltage exceeds the
output voltage.
Setting the Overvoltage Protection Limit
The OV protection circuit should ensure the circuit safe
operation; therefore, the controller should limit the out-
put voltage within the ratings of all MOSFET, diode, and
output capacitor components, while providing sufficient
output voltage for LED current regulation. The OV pin is
connected to the center tap of a resistive voltage-
divider (R1 and R2 in Figure 1) from the high-voltage
output. When the controller detects the OV pin voltage
reaching the threshold V OV_TH , typically 1.23V, OV pro-
tection is activated. Hence, the step-up converter out-
put overvoltage protection point is:
frequency is less than 10mA:
Q g ( MAX ) × f OSC < 10 mA
V OUT ( OVP ) = V OV _ TH × ( 1 +
R 1
R 2
)
For example, the Si3458DV is specified with 16nC of
In Figure 1, the output OVP voltage is set to:
max total gate charge at Vg = 10V. For 5V of gate
drive, the required gate charge is 8nC, which equates
to 8mA at 1MHz.
V OUT ( OVP ) = 1 . 23 V × ( 1 +
1 M Ω
37 . 4 k Ω
) = 34 . 1 V
______________________________________________________________________________________
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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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