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SP7663 Datasheet(PDF) 9 Page - Sipex Corporation |
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SP7663 Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 19 page  9 Feb2-07 Rev O SP7663 Wide Input Voltage Range 6A, 600kHz Buck Regulator © 2007 Sipex Corporation 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 TheSP7663containsapairofintegratedlow resistance N-channel switches designed to drive up to 6Aof output current. Care should be taken to de-rate the output current based on the thermal conditions in the system such as ambient temperature, airflow and heat sinking.Maximumoutputcurrentcouldbe limited by thermal limitations of a particular application by taking advantage of the inte- grated-over-temperature protective scheme employed in the SP7663. The SP7663 incor- porates a built-in overtemperature protection to prevent internal overheating. Setting Output Voltages The SP7663 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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