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ACE701D 参数 Datasheet PDF下载

ACE701D图片预览
型号: ACE701D
PDF下载: 下载PDF文件 查看货源
内容描述: PFM升压型DC /高效率和低噪声DC转换器 [PFM STEP-UP DC/DC Converter with High Efficiency and Low Noise]
分类和应用: 转换器
文件页数/大小: 14 页 / 1059 K
品牌: ACE [ ACE TECHNOLOGY CO., LTD. ]
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ACE701D  
PFM STEP-UP DC/DC Converter with High Efficiency and Low Noise  
Detailed Description  
The ACE701D series are boost structure, voltage-type pulse-frequency modulation(PFM) step-up  
DC-DC converter. Only three external components are necessary: an inductor, an output filter capacitor  
and a schottky diode. And the converters low noise and low ripple output voltage can be adjusted from  
2.5V to 5.0V, 0.1V step. By using the depletion technics, the quiescent current drawn from power source  
is lower than 7uA. The high efficiency device consists of resistors for output voltage detection and  
trimming, a start-up voltage circuit, an oscillator, a reference circuit, a PFM control circuit, a switch  
protection circuit and a driver transistor.  
The PFM control circuit is the core of the ACE701D IC. This block controls power switch on duty cycle to  
stabilize output voltage by calculating results of other blocks which sense input voltage, output voltage,  
output current and load conditions. In PFM modulation system, the frequency and pulse width is fixed.  
The duty cycle is adjusted by skipping pulses, so that switch on-time is changed based on the conditions  
such as input voltage, output current and load. The oscillate block inside ACE701D provides fixed  
frequency and pulse width wave.  
The reference circuit provides stable reference voltage to output stable output voltage. Because internal  
trimming technology is used, The chip output change less than ±2%. At the same timethe problem of  
temperature-drift coefficient of output voltage is considered in design, so temperature-drift coefficient of  
output voltage is less than 100ppm/℃。  
High-gain differential error amplifier guarantees stable output voltage at difference input voltage  
and load. In order to reduce ripple and noise, the error amplifier is designed with high band-with.  
Though at very low load condition, the quiescent current of chip do effect efficiency certainly. The four  
main energy loss of Boost structure DC-DC converter in full load are the ESR of inductor, the voltage of  
Schottky diode, on resistor of internal N-channel MOSFET and its driver. In order to improve the efficiency,  
ACE701D integrates low on-resistor N-channel MOSFET and well design driver circuits. The switch  
energy loss is limited at very low level.  
Selection of the External Components  
Thus it can be seen, the inductor and schottky diode affect the conversion efficiency greatly. The  
inductor and the capacitor also have great influence on the output voltage ripple of the converter. So it is  
necessary to choose a suitable inductor, a capacitor and a right schottky diode, to obtain high efficiency,  
low ripple and low noise.  
Before discussionwe define DVout-Vin / Vout  
(1) Inductor Selection  
Above all, we should define the minimum value of the inductor that can ensure the boost DC-DC to  
operate in the continuous current-mode condition.  
LminD(1-D)2RL / 2f  
The above expression is got under conditions of continuous current mode, neglect Schottky diodes  
voltage, ESR of both inductor and capacitor. The actual value is greater that it. If inductors value is less  
than Lminthe efficiency of DC-DC converter will drop greatly, and the DC-DC circuit will not be stable.  
Secondly, consider the ripple of the output voltage,  
ΔI=DVin / Lf  
Im ax=Vin / (1-D)2RL + DVin / 2Lf  
VER 1.3  
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