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RT9715FGQW Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9715FGQW Datasheet(HTML) 8 Page - Richtek Technology Corporation |
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8 / 15 page  RT9715 8 DS9715-03 April 2011 www.richtek.com Fault Flag The RT9715 series provides a FLG signal pin which is an N-Channel open drain MOSFET output. This open drain output goes low when current limit or the die temperature exceeds 120 °C approximately. The FLG output is capable of sinking a 10mA load to typically 200mV above ground. The FLG pin requires a pull-up resistor, this resistor should be large in value to reduce energy drain. A 100k Ω pull-up resistor works well for most applications. In the case of an over-current condition, FLG will be asserted only after the flag response delay time, tD, has elapsed. This ensures that FLG is asserted only upon valid over-current conditions and that erroneous error reporting is eliminated. For example, false over-current conditions may occur during hot-plug events when extremely large capacitive loads are connected and causes a high transient inrush current that exceeds the current limit threshold. The FLG response delay time tD is typically 12ms. Under-Voltage Lockout Under-voltage lockout (UVLO) prevents the MOSFET switch from turning on until input the voltage exceeds approximately 1.7V. If input voltage drops below approximately 1.3V, UVLO turns off the MOSFET switch. Under-voltage detection functions only when the switch is enabled. Current Limiting and Short-Circuit Protection The current limit circuitry prevents damage to the MOSFET switch and the hub downstream port but can deliver load current up to the current limit threshold of typically 2A through the switch of the RT9715A/B, 1.5A for RT9715C/D, 1.1A for RT9715E/F and 0.7A for RT9715G/H respectively. When a heavy load or short circuit is applied to an enabled switch, a large transient current may flow until the current limit circuitry responds. Once this current limit threshold is exceeded, the device enters constant current mode until the thermal shutdown occurs or the fault is removed. Thermal Shutdown Thermal protection limits the power dissipation in RT9715. When the operation junction temperature exceeds 120 °C, the OTP circuit starts the thermal shutdown function and Applications Information The RT9715 is a single N-MOSFET high-side power switches with enable input, optimized for self-powered and bus-powered Universal Serial Bus (USB) applications. The RT9715 is equipped with a charge pump circuitry to drive the internal N-MOSFET switch; the switch's low RDS(ON), 90m Ω, meets USB voltage drop requirements; and a flag output is available to indicate fault conditions to the local USB controller. Input and Output VIN (input) is the power source connection to the internal circuitry and the drain of the MOSFET. VOUT (output) is the source of the MOSFET. In a typical application, current flows through the switch from VIN to VOUT toward the load. If VOUT is greater than VIN, current will flow from VOUT to VIN since the MOSFET is bidirectional when on. Unlike a normal MOSFET, there is no parasitic body diode between drain and source of the MOSFET, the RT9715 prevents reverse current flow if VOUT is externally forced to a higher voltage than VIN when the chip is disabled (VEN < 0.8V or VEN > 2V). D G S D G S Normal MOSFET RT9715 Chip Enable Input The switch will be disabled when the EN/EN pin is in a logic low/high condition. During this condition, the internal circuitry and MOSFET will be turned off, reducing the supply current to 0.1uA typical. Floating the EN/EN may cause unpredictable operation. EN should not be allowed to go negative with respect to GND. The EN/EN pin may be directly tied to VIN (GND) to keep the part on. Soft Start for Hot Plug-In Applications In order to eliminate the upstream voltage droop caused by the large inrush current during hot-plug events, the “soft- start” feature effectively isolates the power source from extremely large capacitive loads, satisfying the USB voltage droop requirements. |
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