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RT9259GS Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9259GS Datasheet(HTML) 8 Page - Richtek Technology Corporation |
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8 / 15 page  RT9259 8 DS9259-03T00 August 2007 www.richtek.com Figure 2 Application Information Introduction The RT9259 is a dual-channel DC/DC controller specifically designed to deliver high quality power where 12V power source is available. This part consists of a synchronous buck controller and an LDO controller. The synchronous buck controller integrates internal MOSFET drivers that support 12V+12V bootstrapped voltage for high efficiency power conversion. The bootstrap diode is built-in to simplify the circuit design and minimize external part count. The LDO controller drives an external N-MOSFET for lower power requirement. Internal 5VDD Regulator It is highly recommended to power the RT9259 with well- decoupled 12V to VCC12 pin. VCC12 powers the RT9259 control circuit, low side gate driver and bootstrap circuit for high side gate driver. A bootstrap diode is embedded to facilitates PCB design and reduce the total BOM cost. No external Schottky diode is required. The RT9259 integrates MOSFET gate drives that are powered from the VCC12 pin and support 12V + 12V driving capability. Converters that consist of RT9259 feature high efficiency without special consideration on the selection of MOSFETs. An internal linear regulator regulates VCC12 input to a 5VDD voltage for internal control logic circuit. No external bypass capacitor is required for filtering the 5VDD voltage. This further facilitates PCB design and reduces the total BOM cost. Power On Reset The RT9259 automatically initializes upon applying input power (at the VCC12) pin. The power on reset function (POR) continually monitors the input bias supply voltage at the VCC12 pin. The VCC12V POR level is typically 9.6V at VCC12V rising. Frequency Setting and Shut Down Connecting a resistor RRT from the RT_DIS pin to GND sets the operation frequency. The relation can be roughly expressed in the equation. When let open, the free running frequency is 230kHz typically. Figure 1 shows the operation frequency vs. RRT for quick reference. Figure 1. RT vs. fsw at Low Frequency Shorting the RT_DIS pin to GND with an external signal- level MOSFET shuts down the device. This allows flexible power sequence control for specified application. The RT_DIS pin threshold voltage is 0.4V typically. VIN1 Detection The RT9259 continuously generates a 10kHz pulse train with 1 μs pulse width to turn on the upper MOSFET for detecting the existence of VIN1 after VCC12V POR and RT_DIS enabled as shown in Figure 2. PHASE pin voltage is monitored during the detection duration. If the PHASE voltage crosses 1.5V four times, VIN1 existence is recognized and the RT9259 initiates its soft start cycle as described in next section. (kHz) R 7700 kHz 30 2 f RT OSC + ≅ 0 200 400 600 800 1000 1200 1400 10 100 1000 RRT (kohm) (k Ω) + - V IN1 POR_H PHASE UGATE PHASE_M 1.5V Internal Counter will count (V PHASE > 1.5V) four times (rising & falling) to recognize V IN1 is ready. 1st 2nd 3rd 4th PHASE waveform |
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Similar Description - RT9259GS |
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