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RT7259 Datasheet(PDF) 3 Page - Richtek Technology Corporation |
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RT7259 Datasheet(HTML) 3 Page - Richtek Technology Corporation |
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3 / 15 page  3 DS7259-00 January 2012 www.richtek.com RT7259 © Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Function Block Diagram Operation The RT7259 is a synchronous high voltage Buck Converter that can support the input voltage range from 4.5V to 24V and the output current can be up to 10A. The RT7259 uses a constant frequency, current mode architecture. In normal operation, the high side N-MOSFET is turned on when the Switch Controller is set by the oscillator (OSC) and is turned off when the current comparator resets the Switch Controller. While the N-MOSFET is turned off, the external low side N-MOSFET is turned on by BG Driver with 5V driving voltage from Internal Regulator (VCC) until next cycle begins. High side MOSFET peak current is measured by internal RSENSE. The Current Signal is where Slope Compensator works together with sensing voltage of RSENSE. The error amplifier EA adjusts COMP voltage by comparing the feedback signal (VFB) from the output voltage with the internal 0.808V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference, the COMP voltage then rises to allow higher inductor current to match the load current. UV Comparator : If the feedback voltage (VFB) is lower than threshold voltage 0.4V, the UV Comparator's output will go high and the Switch Controller will turn off the high side MOSFET. The output under voltage protection is designed to operate in Hiccup mode. Oscillator (OSC) : The internal oscillator runs at nominal frequency 600kHz and can be synchronized by an external clock in the range between 300kHz and 1.5MHz from EN/ SYNC pin. PGOOD Comparator : When the feedback voltage (VFB) is higher than threshold voltage 0.75V, the PGOOD open drain output will be high impedance. Enable Comparator : Internal 5k Ω resistor and Zener diode are used to clamp the input signal to 3V. A 1.7V reference voltage is for EN logic-high threshold voltage. The EN pin can be connected to VIN through a 100k Ω resistor for automatic startup. Foldback Control : When VFB is lower than 0.7V, the oscillation frequency will be proportional to the feedback voltage. Soft-Start (SS) : An internal current source charges an internal capacitor to build the soft-start ramp voltage (VSS). The VFB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 2ms. Internal Regulator + - Enable Comparator EN/SYNC 1.7V 5k 3V VIN OSC Foldback Control + - 1pF 54pF 300k + - EA 0.808V UV Comparator + - + - Current Comparator 0.4V FB BOOT 45m SW PGOOD GND Current Sense Amplifier Slope Compensator PGOOD Comparator BG Driver BG Switch Controller + - 0.75V VCC RSENSE VCC + OTP COMP VCC VSS VCC Current Signal |
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