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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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SP7662 데이터시트(PDF) 9 Page - Sipex Corporation |
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SP7662 데이터시트(HTML) 9 Page - Sipex Corporation |
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9 / 19 page  9 Nov3-06 Rev AE SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator © 2006 Sipex Corporation Error Amplifier and Voltage Loop The heart of the SP7662 voltage error loop is a high performance, wide bandwidth transconductance amplifier. Because of theamplifier’scurrentlimited(+/-150µA) transconductance, there are many ways to compensatethevoltagelooportocontrolthe COMPpinexternally.Ifasimple,single-pole, single-zero response is desired, then com- pensation can be as simple as an RC circuit toGround.Ifamorecomplexcompensation isrequired,thentheamplifierhasenough bandwidth(45°at4MHz),andenoughgain (60dB)torunTypeIIIcompensationschemes with adequate gain and phase margins at crossover frequencies greater than 50kHz. The common mode output of the error am- plifieris0.9Vto2.2V.Therefore,thePWM voltageramphasbeensetbetween.Vand 2.2V to ensure proper0% to 00% dutycycle capability. The voltage loop also includes two other very important features. One is a nonsynchronousstartupmode.Basically,the synchronousrectifiercannotturnonunless the high side switch has attempted to turn on or the SS pin has exceeded .7V. This featurepreventsthecontrollerfrom“dragging down” the output voltage during startup or in fault modes. GH Voltage GL Voltage V(VIN) 0V -0V -V(Diode) V V(VIN)+V(VCC) BST Voltage V(VCC) TIME SWN Voltage VBST VSWN V(VCC) The second feature is a 00% duty cycle timeout that ensures synchronized refresh- ing of the BST capacitor at very high duty ratios. In the event that the high side NFET is on for 20 continuous clock cycles, a reset isgiventothePWMflipflophalfwaythrough the 2stcycle.ThisforcesGLtoriseforthe cycle, in turn refreshing the BST capacitor. The boost capacitor is used to generate a high voltage drive supply for the high side switch, which is Vcc above ViN. Power MOSFETs The SP7662 contains a pair of integrated lowresistanceN-channelswitchesdesigned to drive up to 2A of output current. Care should be taken to de-rate the output cur- rent based on the thermal conditions in the systemsuchasambienttemperature,airflow andheatsinking.Maximumoutputcurrent could be limited by thermal limitations of a particular application by taking advantage of the integrated-over-temperature protec- tive scheme employed in the SP7662. The SP7662incorporatesabuilt-inovertemperature protection to prevent internal overheating. Setting Output Voltages The SP7662 can be set to different output voltages. The relationship in the following formula is based on a voltage divider from the output to the feedback pin VfB, which is set to an internal reference voltage of 0.80V. Standard1%metalfilmresistorsofsurface mount size 0603 are recommended. VOut = 0.80V [R / R2 + ] => R2 = R / [ ( VOut / 0.80V ) – ] WhereR1=10KΩandforVOut = 0.80V setting, simply remove R2 from the board. Furthermore, one could select the value of the R and R2 combination to meetthe exact output voltage setting by restricting the R resistance range such that 10KΩ < R1 < 100KΩforoverallsystemloopstability. APPLICATIONS INFORMATION |
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