RT9711

Preliminary RT9711 80mΩ, 1.5A High-Side Power Switches with Flag General Description The RT9711 is a low voltage, single N-Channel MOSFET high-side power switch, optimized for self-powered and bus- powered Universal Serial Bus (USB) applications. The RT9711 equipped with a charge pump circuitry to drive the internal MOSFET switch; the switch's low RDS(ON), 80mΩ, meets USB voltage drop requirements; and a flag output is available to indicate fault conditions to the local USB controller. Additional features include soft-start to limit inrush current during plug-in, thermal shutdown to prevent catastrophic switch failure from high-current loads, under-voltage lockout (UVLO) to ensure that the device remains off unless there is a valid input voltage present. The maximum current is limited to typically 2.5A in dual ports in accordance with the USB power requirements, lower quiescent current as 25μA making this device ideal for portable battery-operated equipment. The RT9711 is available in SOT-23-5 and SOP-8 packages requiring minimum board space and smallest components. Features Compliant to USB Specifications Built-In N-Channel MOSFET Typical RDS(ON) : 80mΩ (SOT-23-5), 90mΩ (SOP-8) Output Can Be Forced Higher Than Input (Off-State) Low Supply Current : 25μA Typical at Switch On State 1μA Typical at Switch Off State Guaranteed 1.5A Continuous Load Current Wide Input Voltage Ranges : 2.5V to 5.5V Open-Drain Fault Flag Output Hot Plug-In Application (Soft-Start) 1.7V Typical Under-Voltage Lockout (UVLO) Current Limiting Protection Thermal Shutdown Protection Reverse Current Flow Blocking (no body diode) UL Approved−E219878 RoHS Compliant and 100% Lead (Pb)-Free Applications USB Bus/Self Powered Hubs USB Peripherals ACPI Power Distribution PC Card Hot Swap Notebook, Motherboard PCs Battery-Powered Equipment Hot-Plug Power Supplies Battery-Charger Circuits Ordering Information RT9711 Package Type B : SOT-23-5 S : SOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Note : RichTek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100% matte tin (Sn) plating. Pin Configurations (TOP VIEW) FLG GND EN 1 2 3 4 VIN 5 VOUT Marking Information For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail. GND VIN VIN EN SOT-23-5 8 2 3 4 7 6 5 VOUT VOUT VOUT FLG SOP-8 DS9711-04 March 2007 www.richtek.com 1 RT9711 Typical Application Circuit Pull-Up Resistor (10K to 100K) Supply Voltage 5V VIN 1uF OFF ON FLG RT9711 VOUT GND 10uF 150uF Preliminary Test Circuits RFG USB Controller Over -Current VIN CIN VIN FLG VFLG VOUT + + RT9711 VOUT GND COUT EN VBUS D+ DGND + OFF ON EN RL IL Ferrite Beads Data Note: A low-ESR 150μF aluminum electrolytic or tantalum between VOUT and GND is strongly recommended to meet the 330mV maximum droop requirement in the hub VBUS. (see Application Information Section for further details) Functional Pin Description Pin No. RT9711□B RT9711□S 1 2 3 4 5 5 1 4 2, 3 6, 7, 8 FLG GND EN VIN VOUT Open-Drain Fault Flag Output Ground Chip Enable (Active Low) Power Input Voltage Output Voltage Pin Name Pin Function Function Block Diagram VIN EN Bias UVLO Current Limiting Gate Control Output Voltage Detection Oscillator Charge Pump Thermal Protection VOUT FLG Delay GND www.richtek.com 2 DS9711-04 March 2007 Preliminary Absolute Maximum Ratings (Note 1) RT9711 Supply Voltage --------------------------------------------------------------------------------------------------------- 6.5V Chip Enable Input Voltage ------------------------------------------------------------------------------------------- −0.3V to 6.5V Flag Voltage ------------------------------------------------------------------------------------------------------------ 6.5V Power Dissipation, PD @ TA = 25°C SOT-23-5 ---------------------------------------------------------------------------------------------------------------- 0.4W SOP-8 -------------------------------------------------------------------------------------------------------------------- 0.625W Package Thermal Resistance (Note 5) SOT-23-5, θJA ---------------------------------------------------------------------------------------------------------- 250°C/W SOP-8, θJA -------------------------------------------------------------------------------------------------------------- 160°C/W Junction Temperature ------------------------------------------------------------------------------------------------- 125°C Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 2) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions (Note 3) Supply Input Voltage -------------------------------------------------------------------------------------------------- 2.5V to 5.5V Chip Enable Input Voltage ------------------------------------------------------------------------------------------- 0V to 5.5V Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 5V, CIN = COUT = 1μF, TA = 25°C, unless otherwise specified) Parameter Switch On Resistance Supply Current Symbol SOT23-5 RDS(ON) SOP-8 ISW_ON ISW_OFF Test Conditions VIN = 5V, IOUT = 1A switch on, VOUT = Open switch off, VOUT = Open VIN = 2V to 5.5V, switch on VIN = 2V to 5.5V, switch off VEN = 0V to 5.5V Min -----2.0 ---1.6 ---- Typ 80 90 25 0.1 --0.01 0.5 400 2.5 1.0 20 0.01 Max 100 110 45 1 0.8 --10 -3.2 -400 1 Units mΩ μA V V μA μA μs A A Ω μA EN Threshold Logic-Low Voltage VIL Logic-High Voltage VIH IEN EN Input Current Output Leakage Current Output Turn-On Rise Time Current Limit ILEAKAGE VEN = 5V, RLOAD = 0Ω TON_RISE 10% to 90% of VOUT rising ILIM Current Ramp (< 0.1A/ms) on VOUT VOUT = 0V, measured prior to thermal shutdown ISINK = 1mA VFLG = 5V Short Circuit Fold-Back Current ISC_FB (Hysteresis) FLAG Output Resistance FLAG Off Current RFLG IFLG_OFF To be continued DS9711-04 March 2007 www.richtek.com 3 RT9711 Parameter FLAG Delay Time (Note 4) Symbol tD VUVLO ΔVUVLO TSD ΔTSD Preliminary Test Conditions From fault condition to FLG VIN increasing VIN decreasing Min 5 1.3 ---Typ 12 1.7 0.1 130 20 Max 20 ----Units ms V V °C °C Under-Voltage Lockout Under-Voltage Hysteresis Thermal Shutdown Protection Thermal Shutdown Hysteresis Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. The FLAG delay time is input voltage dependent, see“ Typical Operating Characteristics” graph for further details. Note 5. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. www.richtek.com 4 DS9711-04 March 2007 Preliminary Typical Operating Characteristics Switch On Resistance vs. Temperature 0.25 RT9711 Switch On Resistance vs. Temperature 0.25 SOP-8, VIN = 5V, ILOAD = 1.5A CIN = 1μF/X7R, COUT = 10μF/X7R SOT-23-5, VIN = 5V, ILOAD = 1.5A CIN = 1μF/X7R, COUT = 10μF/X7R Switch On Resistance (Ω) Switch On Resistance (Ω) 0.2 0.2 0.15 0.15 0.1 0.1 0.05 0.05 0 -40 -20 0 20 40 60 80 100 120 0 -40 -20 0 20 40 60 80 100 120 Temperature (°C) Temperature (°C) Switch on Resistance vs. Input Voltage 140 Supply Current vs. Input Voltage 40 35 Switch on Resistance (mΩ) 120 100 80 60 40 20 2 SOT-23-5, ILOAD = 1.5A CIN = COUT = 33μF/Electrolytic SOT-23-5, VEN = 0V, RL = Open CIN = COUT = 33μF/Electrolytic Supply Current (uA) 30 25 20 15 10 5 0 2.5 3 3.5 4 4.5 5 5.5 2 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Input Voltage (V) Supply Current vs. Temperature 30 25 Current Limit vs. Input Voltage 3 2.5 SOT-23-5 VIN = 5V, VEN = 0V, RL = 2.2Ω CIN = 1μF/X7R, COUT = 10μF/X7R Supply Current (uA) Current Limit (A) SOT-23-5 VIN = 5V, VEN = 0V, RL = Open CIN = COUT = 33μF/Electrolytic -40 -20 0 20 40 60 80 100 120 20 15 10 5 0 2 1.5 1 0.5 0 2 2.5 3 3.5 4 4.5 5 5.5 Temperature (°C) Input Voltage (V) DS9711-04 March 2007 www.richtek.com 5 RT9711 Preliminary Current Limit vs. Temperature 3.25 3 EN PinThreshold Voltage vs. Input Voltage 2 VIN = 5V, VEN = 0V, RL = 2.2Ω CIN = 1μF/X7R, COUT = 10μF/X7R EN Threshold Voltage (V) 1.6 SOT-23-5, Switch Off CIN = COUT = 33μF/Electrolytic ILOAD = 100mA Current Limit (A) 2.75 SOP-8 2.5 1.2 SOT-23-5 2.25 2 1.75 1.5 -40 -20 0 20 40 60 80 100 120 0.8 0.4 0 2 2.5 3 3.5 4 4.5 5 5.5 Temperature (°C) Input Voltage (V) EN Pin Threshold Voltage vs. Temperature 2.4 Turn-Off Leakage Current vs. Temperature 4 Turn-Off Leakage Current (uA) EN Pin Threshold Voltage (V) 2 1.6 1.2 0.8 0.4 0 SOT-23-5, VIN = 5V, ILOAD = 100mA CIN = COUT = 33μF/Electrolytic 3.5 3 2.5 2 1.5 1 0.5 0 SOT-23-5, VIN = VEN = 5V CIN = 33μF/Electrolytic COUT = 1uF/X7R RL = 0 Ω -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120 Temperature (°C) Temperature (°C) Turn-On Rising Time vs. Temperature 700 600 500 400 300 200 100 0 -40 -20 0 20 40 60 80 100 120 Turn-Off Falling Time vs. Temperature 100 Turn-On Rising Time (us) Turn-Off Falling Time (us) SOT-23-5, VIN = 5V, RL = 30Ω CIN = 33μF/Electrolytic COUT = 1μF/Electrolytic 80 SOT-23-5, VIN = 5V, RL = 30Ω CIN = 33μF/Electrolytic COUT = 1μF/Electrolytic 60 40 20 0 -40 -20 0 20 40 60 80 100 120 Temperature (°C) Temperature (°C) www.richtek.com 6 DS9711-04 March 2007 Preliminary RT9711 UVLO Threshold vs. Temperature 2.4 2 Swith Off Supply Current vs. Temperature 1 Swith Off Supply Current (uA) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 SOT-23-5, VIN = VEN = 5V CIN = COUT = 33μF/Electrolytic RL = Open UVLO Threshold (V) 1.6 1.2 0.8 0.4 0 SOT-23-5, VIN Increasing VEN = 0V, ILOAD = 15mA CIN = COUT = 33uF/Electrolytic -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120 Temperature (°C) Temperature (°C) FLAG Delay Time vs. Input Voltage 20 Flag Delay Time vs. Temperature 16 15 FLAG Delay Time (ms) Flag Delay Time (ms) 16 14 13 12 11 10 9 8 7 -40 -20 0 12 8 4 SOT-23-5, VEN = 0V CIN = COUT = 33uF/Electrolytic 0 2 2.5 3 3.5 4 4.5 5 5.5 SOT-23-5, VIN = 5V, VEN = 0V CIN = COUT = 33μF/Electrolytic 20 40 60 80 100 120 Input Voltage(V) Temperature Current Limit Transient Response SOT-23-5, VIN = 5V VEN = 0V, RL = 2Ω CIN = COUT = 33μF/Electrolytic Load Transient Response 4.8V 1.5A IOUT (1A/Div) VOUT (1V/Div) IOUT (1A/Div) Time (50μs/Div) SOT-23-5, VIN = 5V VEN = 0V, COUT = 1μF CIN = 33μF/Electrolytic RL = 1kΩ ≥ 2.2Ω Time (1ms/Div) DS9711-04 March 2007 www.richtek.com 7 RT9711 Turn On Response Preliminary Turn Off Response SOT-23-5, VIN = 5V, RL = 30Ω CIN = 33μF/Electrolytic COUT = 1μF/Electrolytic SOT-23-5, VIN = 5V, RL = 30Ω CIN = 33μF/Electrolytic COUT = 1μF/Electrolytic VEN (5V/Div) VEN (5V/Div) VOUT (5V/Div) VOUT (5V/Div) IOUT (200mA/Div) Time (100μs/Div) Time (100μs/Div) UVLO at Rising SOT-23-5, VIN = 5V, VEN = 0V CIN = 33μF/Electrolytic, COUT = 1μF RL = 30Ω UVLO at Falling SOT-23-5, VIN = 5V, VEN = 0V CIN = 33μF/Electrolytic, COUT = 1μF RL = 30Ω VIN (1V/Div) VOUT (1V/Div) Time (1ms/Div) VIN (1V/Div) VOUT (1V/Div) Time (5ms/Div) Flag Response during Short Circuit SOT-23-5, VIN = 5V, RL = 0Ω CIN = COUT = 33μF/Electrolytic Flag Response during Over Load SOT-23-5, VIN = 5V, RL = 2Ω CIN = COUT = 33μF/Electrolytic VEN (5V/Div) VFLG (5V/Div) IOUT (1A/Div) Time (5ms/Div) 10ms VOUT (5V/Div) VFLG (5V/Div) IOUT (1A/Div) Time (5ms/Div) 12ms www.richtek.com 8 DS9711-04 March 2007 Preliminary RT9711 Flag Response with Ramped Load SOT-23-5, VIN = 5V, VEN = 0V CIN = COUT = 33μF/Electrolytic VEN (5V/Div) VLAG (5V/Div) VOUT (5V/Div) IOUT (1A/Div) Time (2.5ms/Div) DS9711-04 March 2007 www.richtek.com 9 RT9711 Applications Information Preliminary The RT9711 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 RT9711 equipped with a charge pump circuitry to drive the internal NMOS switch; the switch's low RDS(ON), 80mΩ, 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 RT9711 prevents reverse current flow if VOUT being externally forced to a higher voltage than VIN when the output disabled (VEN > 2V). 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 RT9711 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 100kΩ 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 voltage exceeds approximately 1.7V. If input voltage drops below approximately 1.6V, 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 2.5A through the switch of RT9711. 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. D S D S G G Normal MOSFET Chip Enable Input RT9711 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 0.1μA 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 RT9711 off. Floating the input may cause unpredictable operation. EN should not be allowed to go negative with respect to GND. www.richtek.com 10 DS9711-04 March 2007 Preliminary 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 shutdown is employed to protect the device from damage if the die temperature exceeds approximately 130°C. The power switch will auto-recover when the IC is coolng down. The thermal hysteresis temperature is about 20°C. Power Dissipation The device’ s junction temperature depends on several factors such as the load, PCB layout, ambient temperature and package type. The output pin of RT9711 can deliver a current up to 1.5A, respectively over the full operating junction temperature range. However, the maximum output current must be derated at higher ambient temperature to ensure the junction temperature does not exceed 125°C. With all possible conditions, the junction temperature must be within the range specified under operating conditions. Power dissipation can be calculated based on the output current and the RDS(ON) of switch as below. PD = RDS(ON) x (IOUT) 2 RT9711 PD(MAX) = ( 125°C − 25°C) / 160°C/W = 0.625 W for SOP-8 packages The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. For RT9711 packages, the Figure 1 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. 0.7 Maximum Power Dissipation (W) Single Layer PCB 0.6 0.5 0.4 0.3 0.2 0.1 0 0 25 50 75 100 125 SOP-8 SOT-23-5 Ambient Temperature (°C) Figure 1. Derating Curves for RT8008 Package Although the devices are rated for 1.5A of output current, but the application may limit the amount of output current based on the total power dissipation and the ambient temperature. The final operating junction temperature for any set of conditions can be estimated by the following thermal equation : PD (MAX) = ( TJ(MAX) − TA ) / θJA Where T J(MAX) i s the maximum operation junction temperature 125°C, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. The junction to ambient thermal resistance θJA is layout dependent. For SOT-23-5 packages, the thermal resistance θJA is 250°C/W on the standard JEDEC 51-3 single-layer thermal test board. And for SOP-8 packages, the thermal resistance θJA is 160°C/W. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = ( 1 25 ° C − 2 5 °C) / 250 °C/W = 0.4 W for SOT-23-5 packages DS9711-04 March 2007 Universal Serial Bus (USB) & Power Distribution The goal of USB is to enable devices from different vendors to interoperate in an open architecture. USB features include ease of use for the end user, a wide range of workloads and applications, robustness, synergy with the PC industry, and low-cost implement- ation. Benefits include self-identifying peripherals, dynamically attachable and reconfigurable peripherals, multiple connections (support for concurrent operation of many devices), support for as many as 127 physical devices, and compatibility with PC Plug-and-Play architecture. The Universal Serial Bus connects USB devices with a USB host: each USB system has one USB host. USB devices are classified either as hubs, which provide additional attachment points to the USB, or as functions, which provide capabilities to the system (for example, a digital joystick). Hub devices are then classified as either Bus-Power Hubs or Self-Powered Hubs. www.richtek.com 11 RT9711 Preliminary Output Filter Capacitor A low-ESR 150μF aluminum electrolytic or tantalum between VOUT and GND is strongly recommended to meet the 330mV maximum droop requirement in the hub VBUS (Per USB 2.0, output ports must have a minimum 120μF of low-ESR bulk capacitance per hub). Standard bypass methods should be used to minimize inductance and resistance between the bypass capacitor and the downstream connector to reduce EMI and decouple voltage droop caused when downstream cables are hot-insertion transients. Ferrite beads in series with VBUS, the ground line and the 0.1 μF bypass capacitors at the power connector pins are recommended for EMI and ESD protection. The bypass capacitor itself should have a low dissipation factor to allow decoupling at higher frequencies. Voltage Drop The USB specification states a minimum port-output voltage in two locations on the bus, 4.75V out of a SelfPowered Hub port and 4.4V out of a Bus-Powered Hub port. As with the Self-Powered Hub, all resistive voltage drops for the Bus-Powered Hub must be accounted for to guarantee voltage regulation (see Figure 7-47 of Universal Serial Specification Revision 2.0 ). The following calculation determines VOUT (MIN) for multiple ports (NPORTS) ganged together through one switch (if using one switch per port, NPORTS is equal to 1) : VOUT (MIN) = 4.75V A Bus-Powered Hub draws all of the power to any internal functions and downstream ports from the USB connector power pins. The hub may draw up to 500mA from the upstream device. External ports in a Bus-Powered Hub can supply up to 100mA per port, with a maximum of four external ports. Self-Powered Hub power for the internal functions and downstream ports does not come from the USB, although the USB interface may draw up to 100mA from its upstream connect, to allow the interface to function when the remainder of the hub is powered down. The hub must be able to supply up to 500mA on all of its external downstream ports. Please refer to Universal Serial Specification Revision 2.0 for more details on designing compliant USB hub and host systems. Over-Current protection devices such as fuses and PTC resistors (also called polyfuse or polyswitch) have slow trip times, high on-resistance, and lack the necessary circuitry for USB-required fault reporting. The faster trip time of the RT9711 power distribution allow designers to design hubs that can operate through faults. The RT9711 have low on-resistance and internal faultreporting circuitry that help the designer to meet voltage regulation and fault notification requirements. Because the devices are also power switches, the designer of self-powered hubs has the flexibility to turn off power to output ports. Unlike a normal MOSFET, the devices have controlled rise and fall times to provide the needed inrush current limiting required for the bus-powered hub power switch. Supply Filter/Bypass Capacitor A 1μF low-ESR ceramic capacitor from VIN to GND, located at the device is strongly recommended to prevent the input voltage drooping during hot-plug events. However, higher capacitor values will further reduce the voltage droop on the input. Furthermore, without the bypass capacitor, an output short may cause sufficient ringing on the input (from source lead inductance) to destroy the internal control circuitry. The input transient must not exceed 6.5V of the absolute maximum supply voltage even for a short duration. − [ II x ( 4 x RCONN + 2 x RCABLE ) ] − − VPCB (0.1A x NPORTS x RSWITCH ) Where RCONN : Resistance of connector contacts (two contacts per connector) RCABLE : Resistance of upstream cable wires (one 5V and one GND) RSWITCH : Resistance of power switch (80mΩ typical for RT9711) VPCB : PCB voltage drop www.richtek.com 12 DS9711-04 March 2007 Preliminary The USB specification defines the maximum resistance per contact (RCONN) of the USB connector to be 30mΩ and the drop across the PCB and switch to be 100mV. This basically leaves two variables in the equation : the resistance of the switch and the resistance of the cable. If the hub consumes the maximum current (II) of 500mA, the maximum resistance of the cable is 90mΩ. The resistance of the switch is defined as follows : RSWITCH = { 4.75V VBUS VOUT RT9711 VIN EN GND_BUS FLG GND − 4.4V − [ 0.5A x ( 4 x 30mΩ + 2 x − VPCB } ÷ ( 0.1A x NPORTS ) 90mΩ) ] = (200mV − VPCB ) ÷ ( 0.1A x NPORTS ) If the voltage drop across the PCB is limited to 100mV, the maximum resistance for the switch is 250mΩ for four ports ganged together. The RT9711, with its maximum 100mΩ on-resistance over temperature, easily meets this requirement. PCB Layout In order to meet the voltage drop, droop, and EMI requirements, careful PCB layout is necessary. The following guidelines must be considered : Keep all VBUS traces as short as possible and use at least 50-mil, 2 ounce copper for all VBUS traces. Avoid vias as much as possible. If vias are necessary, make them as large as feasible. Place a ground plane under all circuitry to lower both resistance and inductance and improve DC and transient performance (Use a separate ground and power plans if possible). Place cuts in the ground plane between ports to help reduce the coupling of transients between ports. Locate the output capacitor and ferrite beads as close to the USB connectors as possible to lower impedance (mainly inductance) between the port and the capacitor and improve transient load performance. Locate the RT9711 as close as possible to the output port to limit switching noise. Locate the ceramic bypass capacitors as close as possible to the VIN pins of the RT9711. Board Layout DS9711-04 March 2007 www.richtek.com 13 RT9711 Outline Dimension Preliminary H D L C B b A A1 e Symbol A A1 B b C D e H L Dimensions In Millimeters Min 0.889 0.000 1.397 0.356 2.591 2.692 0.838 0.080 0.300 Max 1.295 0.152 1.803 0.559 2.997 3.099 1.041 0.254 0.610 Dimensions In Inches Min 0.035 0.000 0.055 0.014 0.102 0.106 0.033 0.003 0.012 Max 0.051 0.006 0.071 0.022 0.118 0.122 0.041 0.010 0.024 SOT-23-5 Surface Mount Package www.richtek.com 14 DS9711-04 March 2007 Preliminary RT9711 A H M J B F C I D Dimensions In Millimeters Symbol Min A B C D F H I J M 4.801 3.810 1.346 0.330 1.194 0.170 0.050 5.791 0.400 Max 5.004 3.988 1.753 0.508 1.346 0.254 0.254 6.200 1.270 Dimensions In Inches Min 0.189 0.150 0.053 0.013 0.047 0.007 0.002 0.228 0.016 Max 0.197 0.157 0.069 0.020 0.053 0.010 0.010 0.244 0.050 8-Lead SOP Plastic Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Richtek Technology Corporation Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com DS9711-04 March 2007 www.richtek.com 15