Current-Limited Switch for Single USB Port

Transcription

1 9-57; Rev ; / Current-Limited Switch for Single USB Port General Description The is a current-limited, 6mΩ switch with built-in fault blanking. Its accurate preset current limit of.6a to.6a makes it ideally suited for USB applications. The device s low quiescent supply current () and shutdown current () conserve battery power in portable applications. The operates with inputs from.7 to 5.5, making it ideal for both and 5 systems. A fault signal notifies the microprocessor that the internal current limit has been reached. A ms fault-blanking feature allows momentary faults (such as those caused when hot-swapping into a capacitive load) to be ignored, thus preventing false alarms to the host system. This fault blanking also prevents a fault signal from being issued when the device is powering up. In the, an output overcurrent condition causes the switch to current limit at.6a to.6a and FAULT to go low after the ms blanking period. When the overcurrent condition is removed, FAULT returns to its high-impedance state. The has several safety features to ensure that the USB port is protected. Built-in thermal overload protection limits power dissipation and junction temperatures. The device has an accurate internal current-limiting circuitry to protect the input supply against overload. The is available in a space-saving -pin µmax package. USB Ports and Hubs Notebook Computers Portable Equipment Docking Stations Hot Plug-In Power Supplies Battery-Charger Circuits Applications.5A Guaranteed Output Current Guaranteed.75A Short-Circuit Protection ms Internal Fault-Blanking Timeout No Fault Signal During Power-Up Thermal Shutdown Protection.7 to 5.5 Supply Range Supply Current Small -Pin µmax Package TOP IEW PUT.7 TO FAULT 6 GND Features Ordering Information PART TEMP RANGE P-PACKAGE EUB - C to +85 C µmax Pin Configuration µmax Typical Operating Circuit PUT OFF FAULT GND Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATGS, (), FAULT to GND...-. to +6 to GND...-. to ( +.) Maximum Continuous Switch Current...A (internally limited) Short Circuit to GND...Continuous Continuous Power Dissipation (T A = +7 C) -Pin µmax (derate 5.6mW/ C above +7 C)...mW Operating Temperature Range...- C to +85 C Storage Temperature Range C to +5 C Lead Temperature (soldering, s)...+ C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and 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 affect device reliability. ELECTRICAL CHARACTERISTICS ( = 5, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +5 C.) PARAMETER Operating oltage Quiescent Current Off Supply Current Undervoltage Lockout Off Switch Leakage Continuous Short-Circuit Current Limit Input Logic Low oltage Input Logic High oltage Input Leakage FAULT Output Logic Low oltage SYMBOL Timer not running 5 I Q = GND, I = Timer running 5 ULO I SC IL IH OL = = = 5.5 Rising edge, m hysteresis = = 5.5, = GND shorted to GND =.7 to 5.5 =.7 to.6 = or GND I SK = ma, = CDITIS T A = +5 C T A = C to +85 C M TYP MAX T A = +5 C =. to On-Resistance R =. to T A = C to +85 C = 7 8 Current Limit I LIMIT = =.7 to ±. UNITS mω ma ma FAULT Output High Leakage Current Fault-Blanking Timeout Period Startup Time Switch Turn-On Time Switch Turn-Off Time Thermal Shutdown Threshold t FB t t OFF = FAULT = 5.5 From overcurrent condition to FAULT assertion = 5, C = 5µF, R L = 5Ω, from driven low to 5% full 6 I LOAD = ma 8 µs I LOAD = ma 6 µs 65 ms ms C

3 ELECTRICAL CHARACTERISTICS ( = 5, T A = - C to +85 C, unless otherwise noted.) (Note ) PARAMETER SYMBOL CDITIS M TYP MAX Operating oltage 5.5 Quiescent Current I Q = GND, I =, timer not running 5 Off Supply Current = = = 5.5 Undervoltage Lockout ULO Rising edge, m hysteresis..9 UNITS Off Switch Leakage = = 5.5, = GND On-Resistance R =. to 5.5 = 5 8 mω Current Limit I LIMIT =.5 6 ma Continuous Short-Circuit Current Limit shorted to GND 75 ma Input Logic Low oltage IL = to Input Logic High oltage IH = to.6 =.7 to 5.5. Input Leakage = or GND ± FAULT Output Logic Low oltage OL I SK = ma, =. FAULT Output High Leakage Current Fault-Blanking Timeout Period Switch Turn-On Time Switch Turn-Off Time t FB t t OFF = FAULT = 5.5 From overcurrent condition to FAULT assertion 6 I LOAD = ma µs I LOAD = ma µs ms Note : Specifications to - C are guaranteed by design, not production tested.

4 ( = 5, T A = +5 C, unless otherwise noted.) QUIESCENT CURRENT () QUIESCENT CURRENT vs. PUT OLTAGE 6 () = GND ( ) I = O 8 6 toc QUIESCENT CURRENT () QUIESCENT CURRENT vs. TEMPERATURE 6 = 5 5 Typical Operating Characteristics = toc OFF SUPPLY CURRENT (na). OFF SUPPLY CURRENT vs. TEMPERATURE () = (GND) toc PUT OLTAGE () OFF SWITCH CURRENT vs. TEMPERATURE NORMALIZED -RESISTANCE vs. TEMPERATURE NORMALIZED PUT CURRENT vs. PUT OLTAGE OFF SWITCH CURRENT (na). N () = (GND) toc NORMALIZED R I = 5mA toc5 NORMALIZED PUT CURRENT SHORT-CIRCUIT CURRENT I LIMIT toc PUT OLTAGE () TURN- TIME vs. TEMPERATURE TURN-OFF TIME vs. TEMPERATURE 6 I LOAD = 5mA = toc7 7 6 I LOAD = 5mA = 5 toc8 5 t (µs) 8 6 = 5 toff (µs) =

5 ( = 5, T A = +5 C, unless otherwise noted.) FAULT-BLANKG TIME (ms) 8 6 FAULT-BLANKG TIME vs. TEMPERATURE I = 85mA = OR toc9 Typical Operating Characteristics (continued) CURRENT-LIMIT AND FAULT RESPSE ms/div CH =, m/div, AC-COUPLED; CH =, 5/div; CH = FAULT, 5/div; CH = I, 5mA/div toc CURRENT-LIMIT RESPSE µs/div CH =, m/div, AC-COUPLED; CH =, 5/div; CH = FAULT, 5/div; CH = I, A/div toc SWITCH TURN- TIME SWITCH TURN-OFF TIME STARTUP TIME (TYPICAL USB APPLICATI) toc toc C L = 5µF R L = 5Ω toc FULL CURRENT LIMIT CHARGES CAPACITOR µs/div CH =, 5/div; CH =, 5/div; CH = FAULT, 5/div; CH = I, ma/div µs/div CH =, 5/div; CH =, 5/div; CH = FAULT, 5/div; CH = I, ma/div FOLDBACK CURRENT LIMIT ms/div RESISTOR LOAD CURRENT CH =, 5/div; CH =, 5/div; CH = I, 5mA/div; CH = FAULT, 5/div 5

6 Pin Description P NAME FUNCTI,, 9 Input. P-channel MOSFET source. Connect all pins together and bypass with a µf ceramic capacitor to ground.,, 8, Switch Output. P-channel MOSFET drain. Connect all pins together and bypass with a.µf capacitor to ground. 5 Active-Low Switch On Input. A logic low turns the switch on. 6 GND Ground 7 FAULT Fault-Indicator Output. This open-drain output goes low when the device is in thermal shutdown, undervoltage lockout, or on a sustained (>ms) current-limit condition. FAULT N Figure. Functional Diagram P P REPLICA AMPLIFIER ms TIMER HOT CTROL CIRCUITRY P CURRENT-LIMIT AMPLIFIER. GND Continuous Short-Circuit Protection The is a foldback short-circuit-protected switch. In the event of an output short-circuit or currentoverload condition, the current through the switch is foldback-current-limited to 5mA continuous. Thermal Shutdown The features thermal shutdown. The switch turns off and the FAULT output goes low immediately (no fault blanking) when the junction temperature exceeds +65 C. When the cools C, the switch turns back on. If the fault short-circuit condition is not removed, the switch cycles on and off, resulting in a pulsed output. FAULT Indicator The provides a fault output (FAULT). A kω pullup resistor from FAULT to provides a logic control signal. This open-drain output goes low when any of the following conditions occur: The input voltage is below the undervoltage lockout (ULO) threshold. The die temperature exceeds the thermal shutdown temperature limit of +65 C. The device is in current limit and the ms faultblanking period is exceeded. Detailed Description The P-channel MOSFET power switch limits output current to.6a (min) to.6a (max). When the output current is increased beyond the current limit (ILIMIT), the current also increases through the replica switch (I / 65). The current-limit error amplifier compares the voltage to the internal. reference and regulates the current back to the I LIMIT. This switch is not bidirectional; therefore, the input voltage must be higher than the output voltage. Fault Blanking The features ms fault blanking. Fault blanking allows current-limit faults, including momentary short-circuit faults that occur when hot-swapping a capacitive load, and also ensures that no fault is issued during power-up. When a load transient causes the device to enter current limit, an internal counter starts. If the load fault persists beyond the ms fault-blanking timeout, the FAULT output asserts low. Ensure that the s input is adequately bypassed to prevent input glitches from triggering spurious FAULT outputs. Input voltage glitches less than 5m do not cause a 6

7 spurious FAULT output. Load-transient faults less than ms (typ) do not cause a FAULT output assertion. Only current-limit faults are blanked. Die overtemperature faults and input voltage droops below the ULO threshold cause an immediate fault output. Applications Information Input Capacitor To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from to GND. A µf ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce the voltage drop at the input (see Figure ). Output Capacitor Connect a.µf capacitor from to GND. This capacitor helps prevent inductive parasitics from pulling negative during turn-off. Layout and Thermal Dissipation To optimize the switch-response time to output shortcircuit conditions, it is very important to keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors as close to the device as possible (no more than 5mm). All and all pins must be connected with short traces to the power bus. Wide power bus planes provide superior heat dissipation through the switch and pins. Figure shows suggested pin connections for a single-layer board. Under normal operating conditions, the package can dissipate and channel heat away. Calculate the maximum power dissipation as follows: P = (I LIMIT ) R where ILIMIT is the preset current limit (.A max) and R is the on-resistance of the switch (5mΩ max). When the output is short-circuited, foldback-current-limiting activates and the voltage drop across the switch equals the input supply. The power dissipated across the switch increases, as does the die temperature. If the fault condition is not removed, the thermal-overload protection circuitry activates (see the Thermal Shutdown section). Wide power-bus planes connected to and and a ground plane in contact with the device help dissipate additional heat. TRANSISTOR COUNT: 75 Chip Information PUT.7 TO 5.5 PUT µf.µf* kω FAULT 9 OFF GND 5 FAULT GND *USB SPECIFICATIS REQUIRE A LARGER CAPACITOR Figure. Typical Application Circuit Figure. and Cross Connections for a Single-Layer Board 7

8 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to LUMAX.EPS Note: does not have an exposed pad. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.