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RT9204CS Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9204CS Datasheet(HTML) 8 Page - Richtek Technology Corporation |
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8 / 14 page  RT9204 Preliminary www.richtek-ic.com.tw DS9204-00 February 2002 8 Functional Description The RT9204 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 RT9204 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 RT9204 is powered by an external bootstrap circuit, as the Fig.1. The boot capacitor, CBOOT, generates a floating reference at the PHASE node. Typically a 0.1 µF CBOOT is enough for most of MOSFETs used with the RT9204. The voltage drop between BOOT and PHASE node is refreshed to a voltage of VCC – diode drop (VD) while the low side MOSFET turning on. Fig.1 Single 5V power Supply Operation Dual Power Operation The RT9204 was 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 RT9204 is ideal for higher current application due to the higher gate driving capability, VUGATE = 7V. A RC (10 Ω/1µF) filter is also recommended at BOOT pin to prevent the ringing induced from fast power on, as shown in Fig.2. Fig.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. Under Voltage and Over Voltage Protection The voltage at FB pin is monitored and protected against OC (over current), UV (under voltage), and OV (over voltage). The UV threshold is 0.5V and OV- threshold is 1.0V. Both UV/OV detection have 30 µS triggered delay. When OC or UV trigged, a hiccup re- start sequence will be initialized, as shown in Fig.3. Only 3 times of trigger are allowed to latch off. Hiccup is disabled during soft-start interval. + BOOT UGATE PHASE RT9204 D1 0.1 µF 5V R1 C2 1 µF VCC + BOOT UGATE 6.0V Regulator 5V R1 10 C2 1 µF C1 1 µF 12V VCC RT9204 |
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