Datasheet RT1720 (Richtek) - 4

RT1720 Operation
̅̅̅̅̅̅̅ The RT1720 is an over-voltage and over-current charged by a 25A pull-up current and at 1.2V the FLT protection regulator that drives an external N-MOSFET output goes low, signaling a fault. The load switch load switch. If the input voltage rises above the voltage MOSFET remains on until VTMR reaches 1.4V, giving set-point (set by the voltage divider at FB) the RT1720 time for any system housekeeping to occur before the linear-regulates the load voltage using the external MOSFET turns off. load switch MOSFET, until the adjustable fault timer If the fault condition ends or the MOSFET switch is trips and turns the MOSFET off to prevent overheating. turned off (eliminating the fault), the capacitor at TMR is If the load draws more than the current set-point (set by slowly discharged by a 3.5A pull-down current. When the external sense resistor connected between SNS VTMR reaches 0.5V, GATE begins charging up and and VCC) the IC controls the load switch MOSFET as a turns on the load switch, restarting the load current source to limit the output current, until the fault automatically. The slower TMR discharge rate allows a timer trips and turns off the MOSFET. These functions low duty factor of operation, to prevent overheating the protect the load and system from faults and surges MOSFET or the load. while potentially allowing the load to operate through The RT1720 open-drain PGOOD output rises when the short-term voltage or current overloads. load switch turns on fully and the MOSFET’s source The RT1720 operates over a wide supply voltage approaches its drain voltage. This output signal can be range of 5V to 80V and can withstand reverse supply used to enable downstream devices or to signal a voltages up to 60V below ground without damage. system that normal operation can begin. Whenever it is enabled and no fault is detected, its The IC’s SH ̅̅̅̅D ̅̅ N ̅̅̅ input disables all functions and internal charge pump generates a gate-source voltage reduces the VCC quiescent current down to 7A. of about 12V, fully enhancing the load switch MOSFET to minimize dissipation and voltage loss. During a fault condition, an external capacitor (at TMR) is slowly Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS1720-01 November 2015 4