参数资料
型号: AP8800FNG-7
厂商: Diodes Inc
文件页数: 4/13页
文件大小: 0K
描述: IC LED DRIVER HIGH BRIGHT 10DFN
特色产品: LED Driver Solutions
AP880X Series Step-Down DC/DC Converter
标准包装: 1
恒定电流:
拓扑: PWM,降压(降压)
输出数: 1
内部驱动器:
类型 - 主要: 背光
类型 - 次要: 高亮度 LED(HBLED)
频率: 600kHz
电源电压: 8 V ~ 28 V
输出电压: 28V
安装类型: 表面贴装
封装/外壳: 10-UFDFN 裸露焊盘
供应商设备封装: DFN3030-10
包装: 标准包装
工作温度: -40°C ~ 85°C
产品目录页面: 1138 (CN2011-ZH PDF)
其它名称: AP8800FNGDIDKR
AP8800
Application Information
AP8800 Operation
The AP8800 is a hysteretic LED current switching regulator sometimes known as an equal ripple switching regulator. In normal operation, when
voltage is applied at +V IN (See Figure 1), the AP8800 internal switch is turned on. Current starts to flow through sense resistor R 1 , inductor L1,
and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +V IN , and the inductor L1 (See Figure 2).
Figure 1 Typical Configuration
Figure 2 Typical Switching Waveform
This rising current produces a voltage ramp across R SET . The internal circuit of the AP8800 senses the voltage across R SET and applies a
proportional voltage to the input of the internal comparator.
When this voltage reaches an internally set upper threshold, the internal switch is turned off. The inductor current continues to flow through R SET ,
L1, the LEDs and the schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop
of the LEDs and the schottky diode.
This decaying current produces a falling voltage at R SET , which is sensed by the AP8800. A voltage proportional to the sense voltage across
R SET is applied at the input of the internal comparator. When this voltage falls to the internally set lower threshold, the internal switch is turned on
again. This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R SET, with a switching current
determined by the input voltage and LED chain voltage.
In normal operation the off time is relatively constant (determined mainly by the LED chain voltage) with only the on-time varying as the input
voltage changes. At duty cycles up to around 80% the ramp of the LED/switch current is very linear; however, as the duty cycle approaches 95%
the LED current ramp starts to become more exponential. This has two effects:
1.
2.
The overall on time starts to increase lowering the overall switching frequency.
The average LED current starts to increase – which may impact accuracy.
AP8800
Document number: DS31764 Rev. 7 - 2
4 of 13
www.diodes.com
August 2012
? Diodes Incorporated
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