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FSP3603TCAD Datasheet(PDF) 3 Page - FOSLINK SEMICONDUCTOR CO.,LTD |
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FSP3603TCAD Datasheet(HTML) 3 Page - FOSLINK SEMICONDUCTOR CO.,LTD |
3 / 9 page 1.2MHZ MICROPOWER SYNCHRONOUS STEP-UP CONVERTER 2007-4-19 3/9 FSP3603 FUNCTIONAL BLOCK DIAGRAM FUNCTION DESCROPTION Operation The FSP3603 is a synchronous step-up DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency over the full load current range. It operates at a fixed switching frequency of 1.2MHz, and uses the slope compensated current mode architecture. The device can operate with input voltage even below 1 V and the typical start-up voltage is 0.85V. Synchronous Rectification The FSP3603 integrates a synchronous rectifier to improve efficiency as well as to eliminate the external Schottky diode. The synchronous rectifier is used to reduce the conduction loss contributed by the forward voltage of Schottky diode. The synchronous rectifier is realized by a P-CH MOSFET with gate control circuitry that incorporates relatively complicated timing concerns. Low Voltage Start-Up The FSP3603 can start up at supply voltage down to 0.85V. During start-up, the internal low voltage start-up circuitry controls the NMOS switch to maximum peak inductor current. The device leaves the start-up mode once the VOUT exceeds 2.3V. A Comparator (VOUT GOOG Comp) monitors the output voltage and allows the chip into normal operation once the VOUT exceeds 2.3V. The device is biased by VIN during start-up while biased by VOUT once VOUT exceeds VIN then the operation will be independent of VIN. Current Mode PWM Control The FSP3603 is based on a slope compensated current mode control topology. It operates at a fixed frequency of 1.2MHz. At the beginning of each clock cycle, the main switch (NMOS) is turned on and the inductor current starts to ramp. After the maximum duty cycle or the sense current signal equals to the error amplifier(EA) output, the main switch is turned off and the synchronous switch (PMOS) is turn on. This control topology features cycle by cycle current limiting which can prevent the main switch from overstress and prevent external inductor from saturation. Pulse Skipping Mode At very light load, the FSP3603 automatically switches into Pulse Skipping Mode to improve efficiency. During this mode, the PWM control will skip some pulses to maintain regulation. If the load increases and the output voltage drops, the device will automatically switch back to normal PWM mode and maintain regulation. Antiringing Control An antiringing circuitry is included to remove the high frequency ringing that appears on the SW pin when the inductor current goes to zero. In this case, a ringing on the SW pin is induced due to remaining energy stored in parasitic components of switch and inductor. The antiringing circuitry clamps the voltage internally to battery voltage |
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