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1.2A White LED Regulating Charge Pump for
Camera Flashes and Movie Lights
(Figure 2), the ballast resistors must be small enough to
prevent triggering the overvoltage protection:
R BALLAST < (5.1V - V F ) / I LED
where I LED is the current through each LED and V F is
the forward voltage of the LED at I LED . Within this limit,
larger values of R BALLAST improve LED-to-LED match-
ing but also increase the input voltage where the 2x
charge pump makes the transition to the more efficient
1x LDO mode.
When using voltage regulation (Figure 3), select the
ballast resistors based on the full brightness setting as
follows:
With EN1 high and EN2 high:
R BALLAST = (5.1V - V F ) / I LED
The LED current at the dimmed settings are calculated
as follows:
with EN1 high and EN2 low:
I LED = (4.6V - V F ) / R BALLAST
with EN1 low and EN2 high:
I LED = (3.4V - V F ) / R BALLAST
Note that V F varies as a function of I LED . Typically, LED
manufacturers provide a plot of forward voltage (V F ) vs.
forward current (I LED ) in the LED data sheet.
PC Board Layout and Routing
The MAX1577Y/MAX1577Z are high-frequency
switched-capacitor regulators. For best circuit perfor-
mance, use a solid ground plane and place C IN , C OUT ,
and C1 as close to the IC as possible. Connect the
exposed pad to GND directly under the IC and allow suf-
ficient copper area for cooling. Refer to the MAX1577Z
evaluation kit for an example PC board layout.
Chip Information
TRANSISTOR COUNT: 2482
PROCESS: BiCMOS
10
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相关代理商/技术参数
MAX1577ZETA-T 功能描述:电荷泵 RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube
MAX1577ZEVKIT 功能描述:电荷泵 Evaluation Kit for the MAX1577Y MAX1577Z RoHS:否 制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube
MAX1578ETG 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply 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
MAX1578ETG+ 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply 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
MAX1578ETG+T 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply 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
MAX1578ETG-T 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply 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
MAX1579ETG 功能描述:LED照明驱动器 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
MAX1579ETG+ 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply 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