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RT9202B Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT9202B Datasheet(HTML) 9 Page - Richtek Technology Corporation |
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9 / 14 page  RT9202B 9 DS9202B-03 March 2007 www.richtek.com Application Information The RT9202B operates at either single 5V power supply with a bootstrap UGATE driver or 5V/12V dual-power supply form the ATX SMPS. The dual- power supply is recommended for high current application, the RT9202B can deliver higher gate driving current while operating with ATX SMPS based on dual-power supply. The Bootstrap Operation In a single power supply system, the UGATE driver of RT9202B is powered by an external bootstrap circuit, as the Figure 1. The boot capacitor, CBOOT, generates a floating reference at the PHASE pin. Typically a 0.1 µF CBOOT is enough for most of MOSFETs used with the RT9202B. The voltage drop between BOOT and PHASE is refreshed to a voltage of VCC − diode drop (V D) while the low side MOSFET turning on. Dual Power Operation The RT9202B is designed to regulate a 6.0V at VCC pin automatically when BOOT pin is powered by 12V. In a system with ATX 5V/12V power supply, the RT9202B is ideal for higher current application due to the higher gate driving capability, VUGATE = 7V and VLGATE = 6.0V. A RC (10 Ω/1µF) filter is also recommended at BOOT pin to prevent the ringing induced from fast power on, as shown in Figure 2. 5V VCC LGATE PHASE UGATE BOOT R1 VCC C2 1uF RT9202B 0.1uF D1 5V VCC LGATE UGATE BOOT R1 C2 1uF 1uF 6.0V Regulation 10 C1 12V VCC 5V RT9202B Figure 1. Single 5V power Supply Operation Figure 2. Dual Power Supply Operation Power On Reset The Power-On Reset (POR) monitors the supply voltage (normal +5V) at the VCC pin and the input voltage at the OCSET pin. The VCC POR level is 4.1V with 0.5V hysteresis and the normal level at OCSET pin is 1.5V (see over-current protection). The POR function initiates soft-start operation after all supply voltages exceed their POR thresholds. Soft Start A built-in soft-start is used to prevent surge current from power supply input during power on. The soft-start voltage is controlled by an internal digital counter. It clamps the ramping of reference voltage at the input of error amplifier and the pulse-width of the output driver slowly. The typical soft-start duration is 2ms. Over-Current Protection The over current protection (OCP) function of the RT9202B is triggered when the voltage across the RDS(ON) of upper side MOSFET that developed by drain current exceeds over-current tripping level. An external resistor (ROCSET) programs the over-current tripping level of the PWM converter. As shown on Figure 3 the internal 20 µA current sink (IOCSET) develops a voltage across ROCSET (VSET) that is referenced to VIN. The DRIVE signal enables the over-current comparator (OC). When the voltage across the upper MOSFET (VDS(ON)) exceeds VSET, the over- current comparator trips to set the over-current latch. |
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