LM3525 Single Port USB Power Switch and Over-Current Protection General Description Features The LM3525 provides Universal Serial Bus standard power switch and over-current protection for all host port applications. The single port device is ideal for Notebook PC and Handheld PC applications that supply power to one port. A 1 ms delay on fault flag output prevents erroneous overcurrent reporting caused by inrush currents during the hot-plug events. The LM3525 accepts an input voltage between 2.7V and 5.5V allowing use as a device-based inrush current limiter for 3.3V USB peripherals, as well as Root and Self-Powered Hubs at 5.5V. The Enable input accepts both 3.3V and 5.0V logic thresholds. The small size, low RON, and 1 ms fault flag delay make the LM3525 a good choice for root hubs as well as ganged power control in space-critical self-powered hubs. n 1 ms Fault Flag Delay During Hot-Plug Events n Smooth Turn-On Eliminates Inrush Induced Voltage Drop n UL Recognized Component: REF # 205202 n 1A Nominal Short Circuit Output Current Protects Notebook PC Power Supplies n Thermal Shutdown Protects Device in Direct Short Condition n 500mA Minimum Continuous Load Current n Small SO-8 Package Minimizes Board Space n 2.7V to 5.5V Input Voltage Range n Switch Resistance ≤ 120 mΩ Max. at VIN = 5V n 1µA Max Standby Current n 100 µA Max Operating Current n Undervoltage Lockout (UVLO) Applications n Universal Serial Bus (USB) Root Hubs including Desktop and Notebook PC n USB Monitor Hubs n Other Self-Powered USB Hub Devices n High Power USB Devices Requiring Inrush Limiting n General Purpose High Side Switch Applications Typical Operating Circuit and Connection Diagram DS101055-2 LM3525M-L DS101055-1 DS101055-31 DS101055-30 LM3525M-H © 2000 National Semiconductor Corporation DS101055 www.national.com LM3525 Single Port USB Power Switch and Over-Current Protection January 2000 LM3525 Ordering Information Part Number www.national.com Enable, Delivery Option LM3525M-H Active High Enable, 95 units per rail LM3525M-L Active Low Enable, 95 units per rail LM3525MX-H Active High Enable, 2500 units per reel LM3525MX-L Active Low Enable, 2500 units per reel 2 Package Type SO-8, NS Package Number M08A Operating Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Range 2.7 to 5.5V Operating Ambient Range −40˚C to +85˚C Supply Voltage −0.3V to 6.0V Operating Junction Temperature Range −40˚C to +125˚C Output Voltage −0.3V to 6.0V Storage Temperature Range −65˚C to +150˚C Voltage at All Other Pins −0.3V to 5.5V Lead Temperature (Soldering, 5 seconds) Power Dissipation (TA = 25˚C) (Note 2) TJMAX (Note 2) 700 mW 260˚C ESD Rating (Note 3) 2 kV 150˚C DC Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = 5.0V, EN = 0V (LM3525-L) or EN = VIN (LM3525-H). Symbol Parameter RON On-Resistance IOUT OUT pins continuous output current Conditions Min IN to Out pins VIN = 5V VIN = 2.7V Typ Max Units 80 120 120 160 mΩ 0.5 ISC Short Circuit Output Current (Note 4) ILEAK OUT pins Output Leakage Current EN = VIN (LM3525-L) or EN = GND (LM3525-H), OCTHRESH Over-current Threshold 0.5 RFO FLAG Output Resistance IFO = 10 mA, VIN = 5V IFO = 10 mA, VIN = 2.7V IEN EN/EN Leakage Current EN/EN = 0V or EN/EN = VIN −0.5 VIH EN/EN Input Voltage (Note 5) 2.4 A 1.0 1.5 A 0.15 10 µA 2.25 3.2 A 6 25 8 40 Ω 0.5 1.9 VIL EN/EN Input Voltage VUVLO Under-Voltage Lockout (Note 5) VIN = Increasing VIN = Decreasing 1.9 1.8 1.7 µA V 0.8 V V IDDOFF Supply Current Switch OFF 0.05 1 µA IDDON Supply Current Switch ON 65 100 µA ThSD Overtemperature Shutdown Threshold (Note 4) 135 125 IFH Error Flag Leakage Current TJ Increasing TJ Decreasing VFLAG = 5V 3 0.1 ˚C ˚C 1 µA www.national.com LM3525 Absolute Maximum Ratings (Note 1) LM3525 AC Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = 5.0V. Symbol Parameter Conditions Min Typ Max Units tr OUT Rise Time RL = 10Ω 200 µs tf OUT Fall Time RL = 10Ω 20 µs tON Turn on Delay, EN to OUT RL = 10Ω 200 µs tOFF Turn off Delay, EN to OUT RL = 10Ω 20 µs tOC Over Current Flag Delay RL = 0 1 ms Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. Products are not tested under negative Absolute Maximum conditions. Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX (maximum junction temperature), θJA (junction to ambient thermal resistance), and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PDMAX = (TJMAX − TA)/θJA or the number given in the Absolute Maximum Ratings, which ever is lower. The thermal resistance θJA of the LM3525 in the SO-8 package is 150˚C/W. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 4: Thermal shutdown will protect the device from permanent damage. Note 5: For the LM3525-L, OFF is EN ≥ 2.4V and ON is EN ≤ 0.8V. For the LM3525-H, OFF is EN ≤ 0.8V and ON is EN ≥ 2.4V Pin Description Pin Number Pin Name 1 EN (LM3525-L) EN (LM3525-H) Pin Function 2 FLG Fault Flag (Output): Active-low, open-drain output. Indicates overcurrent, UVLO and thermal shutdown. 3 GND Ground 4, 5 NC Not internally connected. 7 IN Supply Input: This pin is the input to the power switch and the supply voltage for the IC. 6, 8 OUT Enable (Input): Logic-compatible enable input. Switch Output: This pin is the output of the high side switch. Pins 6 & 8 must be tied together. Typical Application Circuit DS101055-3 www.national.com 4 VIN = 5.0V, IL = 500 mA, TA = 25˚C unless otherwise specified. RDSON vs VIN RDSON vs Temperature DS101055-4 Current Limit vs Temperature DS101055-5 Over Current Threshold vs Temperature DS101055-6 Delay vs Temperature DS101055-7 UVLO Threshold DS101055-8 DS101055-9 5 www.national.com LM3525 Typical Performance Characteristics LM3525 Typical Performance Characteristics VIN = 5.0V, IL = 500 mA, TA = 25˚C unless otherwise specified. (Continued) Short Circuit Response Under Voltage Lock Out (UVLO) DS101055-10 Turn-ON/OFF Delay and Rise Time/Fall Time DS101055-11 Short Circuit Current DS101055-13 DS101055-12 www.national.com 6 The LM3525-H and LM3525-L are high side P-Channel switches with active-high and active-low enable inputs, respectively. Fault conditions turn off and inhibit turn-on of the output transistor and activate the open-drain error flag transistor sinking current to the ground. A 0.01 µF ceramic capacitor is recommended on each port directly between the Vbus and ground pins to prevent EMI damage to other components during the hot - detachment. Adequate capacitance must be connected to the input of the device to limit the input voltage drop during a hot-plug event to less than 330 mV. For a few tens of µs, the host must supply the inrush current to the peripheral, charging its bulk capacitance to Vbus. This current is initially supplied by the input capacitor. A 33 µF 16V tantalum capacitor is recommended. In choosing the capacitors, special attention must be paid to the Effective Series Resistance, ESR, of the capacitors to minimize the IR drop across the capacitor’s ESR. INPUT AND OUTPUT IN (Input) is the power supply connection to the control circuitry and the source of the output MOSFET. OUT (Output) is the drain of the output MOSFET. In a typical application circuit, current flows through the switch from IN to OUT towards the load. If VOUT is greater than VIN when the switch is enabled, current will flow from OUT to IN since the MOSFET is bidirectional. SOFT START To eliminate the upstream voltage droop caused by the high in-rush current drawn by the output capacitors, the inrush current is internally limited to 1.0A. THERMAL SHUTDOWN LM3525 is internally protected against excessive power dissipation. In the event of a shorted output or heavy loads that could elevate the die temperature to above approximately 135˚C, the thermal shutdown circuit of the LM3525 will be activated and the power switch turned off. The switch is turned on after die temperature drops by 10˚C. This built-in temperature hysteresis prevents undesirable oscillation of the thermal protection circuit and allows the device to reset itself after it is cooled down. TRANSIENT OVER-CURRENT DELAY In USB applications, it is required that output bulk capacitance is utilized to support hot-plug events. During hot-plug events, inrush currents may also cause the flag to go active. Since these conditions are not valid over-current faults, the USB controller must ignore the flag during these events. High transient current is also generated when switch is enabled and large values of capacitance at the output have to be rapidly charged. The inrush currents created could exceed the short circuit current limit threshold of the device forcing it into the current limit mode. The capacitor is charged with the maximum available short circuit current set by the LM3525. The duration of the inrush current depends on the size of the output capacitance and load current. Since this is not a valid fault condition, the LM3525 delays the generation of the fault flag for 1 ms. If condition persists due to other causes such as a short, a fault flag is generated after a 1 ms delay has elapsed. The LM3525’s 1 ms delay in issuing the fault flag is adequate for most applications. If longer delays are required, an RC filter as shown in Figure 1 may be used. UNDERVOLTAGE LOCKOUT UVLO prevents the MOSFET switch from turning on until input voltage exceeds 1.9V. UVLO shuts off the MOSFET switch and signals the fault flag if input voltage drops below 1.8V. UVLO functions only when device is enabled. CURRENT LIMIT The current limit circuit is designed to protect the system supply, the MOSFET switches and the load from damage caused by excessive currents. The current limit threshold is set internally to allow a minimum of 500 mA through the MOSFET but limit the maximum current to 1.0A typical. FAULT FLAG The fault flag is an open-drain output capable of sinking 10 mA load current to typically 60 mV above ground. The fault flag is active (pulled low) when any of the following conditions are present: undervoltage, current limit, or thermal shutdown. A 1ms delay in reporting fault condition prevents erroneous fault flags and eliminates the need for external RC delay network. DS101055-24 FIGURE 1. Transient Fitter Application Information PCB LAYOUT CONSIDERATIONS In order to meet the USB requirements for voltage drop, droop and EMI, each component used in this circuit must be evaluated for its contribution to the circuit performance as shown in Figure 2. The PCB layout rules and guidelines must be followed. FILTERING The USB specification indicates that “no less than 120 µF tantalum capacitors” must be used on the output of each downstream port. This bulk capacitance provides the short-term transient current needed during a hot plug-in. Current surges caused by the input capacitance of the down stream device could generate undesirable EMI signals. Ferrite beads in series with all power and ground lines are recommended to eliminate or significantly reduce EMI. • 7 Place the switch as close to the USB connector as possible. Keep all Vbus traces as short as possible and use at least 50-mil, 1 ounce copper for all Vbus traces. Solder plating the traces will reduce the trace resistance. www.national.com LM3525 In selecting a ferrite bead, the DC resistance of the wire used must be kept to minimum to reduce the voltage drop. Functional Description LM3525 Application Information • (Continued) • Avoid vias as much as possible. If vias are used, use multiple vias in parallel and/or make them as large as possible. • Place the output capacitor and ferrite beads as close to the USB connector as possible. If ferrite beads are used, use wires with minimum resistance and large solder pads to minimize connection resistance. DS101055-23 FIGURE 2. Self-Powered Hub Per-Port Voltage Drop www.national.com 8 LM3525 Typical Applications DS101055-25 FIGURE 3. SIngle-Port USB Self-Powered Hub DS101055-26 FIGURE 4. Soft-Start Application DS101055-27 FIGURE 5. Inrush Current-limit Application 9 www.national.com LM3525 Single Port USB Power Switch and Over-Current Protection Physical Dimensions inches (millimeters) unless otherwise noted For Order Numbers , see Ordering Information Table NS Package Number M08A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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