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ACE70330AN+ датащи(PDF) 6 Page - ACE Technology Co., LTD. |
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ACE70330AN+ датащи(HTML) 6 Page - ACE Technology Co., LTD. |
6 / 16 page ACE703 Technology White LED PFM Step-Up DC-DC Converter VER 1.2 6 Detailed description The ACE703 series are boost structure, voltage-type pulse-frequency modulation (PFM) step-up DC-DC converter. It can deliver constant current or constant voltage. In constant current application, only five external components are necessary to supply output current from 0 to 500mA:an inductor, an output filter capacitor, a shottky diode, a compensation capacitor and a resistor which adjusts the output current. In constant voltage application, to deliver adjustable and low noise output voltage from 2.5V to 6.0V, only six external components are necessary as well: an inductor, a output filter capacitor, a shottky diode, a compensation capacitor and two resistors for output voltage detect. The ACE703 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, a voltage limit protection circuit and a driver transistor. ● How to determine Rc in constant current application condition We define output current is IOUT ,then Rc can be determined by Rc=VIFB/IOUT For example, if we need Iout=100mA,and we choose the chip of VIFB=200mV,thus Rc=200mV/100mA=2Ω ● How to determine R1,R2 in constant voltage application We define output voltage is Vout, then R1/R2=VOUT/VIFB-1,R2 is in the range of 1KΩ~100KΩ.If we need Vout =3.3V,and we choose the ACE703 of VIFB=400mV and select R2=4KΩ,thus R1=29KΩ. In constant voltage application, we suggest using the high VIFB type ACE703,because there is voltage ripple in existence on feedback voltage. When VIFB is high, the infection of the ripple is less than that of low VIFB type, so the output is more stable. The PFM control circuit is the core of the ACE703 IC. This block controls power switch on/off 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 ACE703 provides fixed frequency and pulse width wave. 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 bandwidth. Though at very low load condition, the quiescent current of chip do affect 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, ACE703 integrates low on-resistor N-channel MOSFET and well designed driver circuits. The switch energy loss is limited at very low level. |
Аналогичный номер детали - ACE70330AN+ |
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Аналогичное описание - ACE70330AN+ |
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