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| KB3511 |
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 KINGBOR
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6 KB3511 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 SIMPLIFIED BLOC DIAGRAM OPERATION 1 2 9 10 8 3 4 11 5 – + – + – + – + EA UVDET OVDET 0.6V 7 0.65V 0.55V – + 0.35V UV OV ITH SWITCHING LOGIC AND BLANKING CIRCUIT S R Q Q RS LATCH Trickle ICOMP IRCMP ANTI SHOOT- THRU Trickle Clamp SLOPE COMP EN SLEEP POR COUNTER 0.6V REF OSC,2.2MHz OSC REGULATOR 2 (IDENTICAL TO REGULATOR 1) PGOOD1 PGOOD2 SHUTDOWN VIN VIN VIN 6 REGULATOR 1 SW1 GND POR GND SW2 5 Ω MODE/SYNC VFB1 RUN1 RUN2 VFB2 The KB3511 uses a constant frequency, current mode architecture. The operating frequency is set at 2.2MHz and can be synchronized to an external oscillator. Both chan- nels share the same clock and run in-phase. To suit a variety of applications, the selectable Mode pin allows the user to trade-off noise for efficiency. The output voltage is set by an external divider returned to the VFB pins. An error amplfier compares the divided output voltage with a reference voltage of 0.6V and adjusts the peak inductor current accordingly. Overvoltage and undervoltage comparators will pull the POR output low if the output voltage is not within ±8.5%. The POR output will go high after 262,144 clock cycles (about 120ms) of achieving regulation. Main Control Loop During normal operation, the top power switch (P-channel MOSFET) is turned on at the beginning of a clock cycle when the VFB voltage is below the the reference voltage. The current into the inductor and the load increases until the current limit is reached. The switch turns off and energy stored in the inductor flows through the bottom switch (N-channel MOSFET) into the load until the next clock cycle. The peak inductor current is controlled by the internally compensated ITH voltage, which is the output of the error amplifier.This amplifier compares the VFB pin to the 0.6V reference. When the load current increases, the VFB volt- age decreases slightly below the reference. This |
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