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RT9706PB Datasheet(PDF) 10 Page - Richtek Technology Corporation |
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RT9706PB Datasheet(HTML) 10 Page - Richtek Technology Corporation |
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10 / 14 page  RT9706 10 DS9706-02 March 2007 www.richtek.com 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. Fault Flag The RT9706 provides a FLG signal pin which is an N-Channel open drain MOSFET output. This open drain output goes low when VOUT < VIN − 1V, current limit or the die temperature exceeds 130 °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. The FLG response delay time tD is typically 12ms. 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. Under-Voltage Lockout Under-voltage lockout (UVLO) prevents the MOSFET switch from turning on until input voltage exceeds approximately 1.7V. If input voltage drops below approximately 1.3V, UVLO turns off the MOSFET switch, FLG will be asserted accordingly. 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 800mA through the switch of RT9706. 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. Applications Information The RT9706 is a single N-Channel MOSFET high-side power switch with active-low enable input, optimized for self-powered and bus-powered Universal Serial Bus (USB) applications. The RT9706 equipped with a charge pump circuitry to drive the internal NMOS switch; the switch's low RDS(ON), 80m 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 a parasitic body diode between drain and source of the MOSFET, the RT9706 prevents reverse current flow if VOUT being externally forced to a higher voltage than VIN when the output disabled (VEN > 2V). Chip Enable Input The switch will be disabled when the EN pin is in a logic high condition. During this condition, the internal circuitry and MOSFET are turned off, reducing the supply current to 0.1 μA typical. The maximum guaranteed voltage for a logic low at the EN pin is 0.8V. A minimum guaranteed voltage of 2V at the EN pin will turn the RT9706 off. Floating the input may cause unpredictable operation. EN should not be allowed to go negative with respect to GND. D G S D G S Normal MOSFET RT9706 Figure 1 |
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Similar Description - RT9706PB |
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