1A Current-Limited Switch for 2 USB Ports

Transcription

1 ; Rev 3; 4/9 1A Current-Limited Switch for 2 USB Ports General Description The current-limited 7mΩ switch with built-in fault blanking provides an accurate, preset 1.4A to 2.1A current limit, making it ideal for dual USB applications. Its low quiescent supply current (16µA) and standby current (1µA) conserve battery power in portable applications. The operates with inputs from 2.7V to 5., making it ideal for both 3V and systems. An overcurrent signal () notifies the microprocessor that the internal current limit has been reached. A 1ms overcurrent-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 blanking also prevents an signal from being issued when the device is powering up. The has several safety features to ensure that the USB port is protected. Built-in thermal-overload protection limits power dissipation and junction temperature. The device also has accurate internal currentlimiting circuitry to protect the input supply against overload. The is offered in a space-saving 8-pin SO package and a 1-pin TDFN package and operates over the extended (-4 C to +85 C) temperature range. Notebook Computers USB Ports USB Hubs Docking Stations Applications Features Accurate Current Limit (1.4A min, 2.1A max) 1ms Internal Blanking Timeout Blanking During Power-Up 125mΩ (max) High-Side MOSFET Short-Circuit and Thermal Protection with Overcurrent Logic Output Undervoltage Lockout 16µA Quiescent Supply Current 1µA (max) Standby Supply Current 2.7V to 5. Supply Range UL Recognized: UL# E PART Ordering Information TEMP RANGE P- PACKAGE TOP MARK ESA+ -4 C to +85 C 8 SO ETB+ -4 C to +85 C 1 TDFN-EP* AQQ *EP = Exposed paddle. +Denotes a lead(pb)-free/rohs-compliant package. Pin Configurations Typical Operating Circuit TOP VIEW PUT 2.7V TO 5. PUT OFF SO ON Pin Configurations continued at end of data sheet. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATGS,, to...-.3v to +6V to...-.3v to (V +.3V) Maximum Switch Current...2.3A (internally limited) Short-Circuit to...continuous Continuous Power Dissipation (T A = +7 C) 8-Pin SO (derate 5.88mW/ C above +7 C)...471mW 1-Pin TDFN (derate 18.5mW/ C above +7 C) mW Operating Temperature Range (extended)...-4 C to +85 C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s)...+3 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 (V =, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS OPERATG CONDITION Input Voltage V V POWER SWITCH T A = +25 C V = 4.4V to Switch Static Drain-Source On- R V = 4.4V to State Resistance DS(ON) mω T A = C to +85 C V = 3V Switch Turn-On Time t ON I LOAD = 4mA 8 2 µs Switch Turn-Off Time t OFF I LOAD = 4mA µs ABLE PUT () High-Level Input Voltage V IH V = 2.7V to 3.6V 2. V = 3.7V to V Low-Level Input Voltage V IL V = 2.7V to 5..8 V Input Current V = V or -1 1 µa Startup Time V =, C = 15µF from driven low to 5% full V 1 ms CURRT LIMIT Overload Output Current I LIMIT Force V to A Short-Circuit Output Current I SC shorted to A SUPPLY CURRT Supply Current, Low-Level Input V = V = V = µa Supply Current, High-Level Timer not running I Q V =, I = Input Timer running 35 µa Supply-Leakage Current UNDERVOLTAGE LK V = V = 5., T A = +25 C.1 2 V = T A = C to +85 C 15 Undervoltage Lockout UVLO Rising edge, 1mV hysteresis V OVERCURRT () Threshold 1.1 A Output Low Voltage V OL I SK = 1mA, V = 3V.4 V µa 2

3 ELECTRICAL CHARACTERISTICS (continued) (V =, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Off-State Current V = V = 1 µa Blanking Timeout Period t BL From overcurrent condition to assertion ms THERMAL SHUTDOWN Thermal Shutdown Threshold 165 C ELECTRICAL CHARACTERISTICS (V =, T A = -4 C to +85 C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS OPERATG CONDITION Input Voltage V V POWER SWITCH Switch Static Drain-Source On-State Resistance V = 4.4V to R DS(ON) V = 3V 15 Switch Turn-On Time t ON I LOAD = 4mA 2 µs Switch Turn-Off Time t OFF I LOAD = 4mA 1 2 µs ABLE PUT () V = 3.V to 3.6V 2. High-Level Input Voltage V IH V = 3.7V to Low-Level Input Voltage V IL V = 3.V to 5..8 V Input Current V = V or -1 1 µa CURRT LIMIT Overload Output Current I LIMIT Force V to A Short-Circuit Output Current I SC shorted to 1.5 A SUPPLY CURRT Supply Current, Low-Level Input V = V = V = 5. 2 µa Supply Current, High-Level Input I Q V =, I =, timer not running 25 µa Supply Leakage Current V = V = 5., V = 15 µa UNDERVOLTAGE LK Undervoltage Lockout UVLO Rising edge, 1mV hysteresis V OVERCURRT () Threshold 1.1 A Output Low Voltage V OL I SK = 1mA, V = 3V.4 V Off-State Current V = V = 1 µa Blanking Timeout Period t BL From overcurrent condition to assertion 6 14 ms Note 1: Specifications to -4 C are guaranteed by design, not production tested. mω V 3

4 (Circuit of Figure 2, V =, T A = +25 C, unless otherwise noted.) QUIESCT CURRT (μa) QUIESCT CURRT vs. PUT VOLTAGE 2 V = 18 I = PUT VOLTAGE (V) toc1 QUIESCT CURRT (μa) QUIESCT CURRT vs. TEMPERATURE 18. I = V = V = 3V Typical Operating Characteristics toc2 OFF SUPPLY CURRT (na) = = OP OFF SUPPLY CURRT vs. TEMPERATURE toc3 OFF SWITCH CURRT vs. TEMPERATURE NORMALIZED ON-RESISTANCE vs. TEMPERATURE NORMALIZED PUT CURRT vs. PUT VOLTAGE OFF SWITCH CURRT (na) = V = toc4 NORMALIZED RON I = 85mA toc5 NORMALIZED PUT CURRT I LIMIT (1.75A) SHORT-CIRCUIT CURRT toc PUT VOLTAGE (V) TURN-ON TIME vs. TEMPERATURE TURN-OFF TIME vs. TEMPERATURE BLANKG TIME vs. TEMPERATURE TURN-ON TIME (μs) I = 85mA C =.1μF V = V = 3V toc7 TURN-OFF TIME (μs) I = 85mA C =.1μF V = V = 3V toc8 BLANKG TIME (ms) V = 3V OR I = 1.75A toc

5 Typical Operating Characteristics (continued) (Circuit of Figure 2, V =, T A = +25 C, unless otherwise noted.) CURRT-LIMIT AND RESPONSE toc1 V AC-COUPLED 1mV/div V, /div CURRT-LIMIT RESPONSE toc11 V AC-COUPLED 5mV/div V, /div V, /div V, /div 2ms/div I, 1A/div 4μs/div I, 2A/div SWITCH TURN-ON TIME toc12 SWITCH TURN-OFF TIME toc13 V, /div V, /div V, /div V, /div V, /div V, /div 2μs/div I, 5mA/div 1μs/div I, 5mA/div STARTUP TIME (TYPICAL USB APPLICATION) toc14 FULL CURRT LIMIT CHARGES CAPACITOR SHORT-CIRCUIT CURRT LIMIT RESISTOR LOAD CURRT 1ms/div V /div V /div I 1A/div V 5A/div 5

6 PACKAGE TDFN SO NAME 6 1 Ground FUNCTION Pin Description 1, 3, 9 2, 3 Inp ut. p - channel M O S FE T sour ce connect al l p i ns tog ether and b yp ass w i th a 1µF cap aci tor g r ound. 5 4 Active-Low Switch Enable Input. A logic-low turns on the switch , 4, 8, 1 6, 7, 8 EP Overcurrent-Indicator Output. This open-drain output goes low when the device is in thermal shutdown or undervoltage lockout, or during a sustained (1ms) current-limit condition. Switch Output. p-channel MOSFET drain connect all pins together and bypass with a.1µf capacitor to ground. TDFN Only. Exposed paddle. Connect to the plane for optimum thermal dissipation. This does not remove the requirement for a proper ground. N P P REPLICA AMPLIFIER 1ms TIMER HOT ON ON 1.24V P CURRT-LIMIT AMPLIFIER Continuous Short-Circuit Protection The is a short-circuit-protected switch. In the event of an output short-circuit condition, the current through the switch is foldback-current-limited to 1A continuous. Thermal Shutdown The has a thermal shutdown feature. The switch turns off and the output goes low immediately (no overcurrent blanking) when the junction temperature exceeds +165 C. When the cools 2 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. Indicator The provides an overcurrent output (). A 1kΩ pullup resistor from 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 2.4V undervoltage lockout (UVLO) threshold. The die temperature exceeds the thermal shutdown temperature limit of +165 C. The device is in current limit for greater than 1ms. CONTROL CIRCUITRY Figure 1. Functional Diagram Detailed Description The p-channel MOSFET power switch limits output current to 1.4A min and 2.1A max. When the output current increases beyond the current limit (I LIMIT ), the current also increases through the replica switch (I / 13). The current-limit error amplifier compares the voltage to the internal 1.24V reference and regulates the current back to the I LIMIT (Figure 1). These switches are not bidirectional; therefore, the input voltage must be higher than the output voltage. Blanking The features 1ms overcurrent blanking. Blanking allows brief current-limit faults, including momentary short-circuit faults that occur when hotswapping a capacitive load, and ensures that no 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 1ms overcurrent blanking timeout, the output asserts low. Ensure that the input is adequately bypassed to prevent input glitches from triggering spurious 6

7 outputs. Input voltage glitches less than 15mV do not cause a spurious output. Load-transient faults less than 1ms (typ) will not cause an output assertion. Only current-limit faults are blanked. Die overtemperature faults and input voltage droops below the UVLO threshold will cause an immediate output. Applications Information Input Capacitor To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from to. A 1µF ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce the voltage drop at the input (Figure 2). PUT 1μF OVERCURRT PUT ON 1kΩ OFF Figure 2. Typical Application Circuit *USB SPECIFICATIONS REQUIRE A HIGHER VALUE CAPACITOR. PUT Output Capacitor Connect a.1µf capacitor from to. This capacitor helps to prevent inductive parasitics from pulling negative during turn-off..1μf* Layout and Thermal Dissipation Important: Optimize the switch response time to output short-circuit conditions by keeping all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors as close as possible to the device (no more than 5mm away). All and pins must be connected with short traces to the power bus. Wide power-bus planes provide superior heat dissipation through the s and pins. Under normal operating conditions, the package can dissipate and channel heat away. Calculate the maximum power dissipation as follows: P = (I LIMIT ) 2 R ON where I LIMIT is the preset current limit (2.1A max) and R ON is the on-resistance of the switch (125mΩ max). When the output is short circuited, foldback-current limiting activates and the voltage drop across the switch equals the input supply voltage. The power dissipated across the switch increases, as does the die temperature. If the fault condition is not removed, the thermaloverload protection circuitry activates (see Thermal Shutdown section). Wide power-bus planes connected to and and a ground plane in contact with the device help dissipate additional heat. Driving Inductive Loads A wide variety of devices (mice, keyboards, cameras, and printers) can load the USB port. These devices commonly connect to the port with cables, which can add an inductive component to the load. This inductance causes the output voltage at the USB port to ring during a load step. The is capable of driving inductive loads, but avoid exceeding the device s absolute maximum ratings. Usually the load inductance is relatively small, and the input includes a substantial bulk capacitance from an upstream regulator as well as local bypass capacitors, limiting overshoot. If severe ringing occurs due to large load inductance, clamp the output below 6V and above -.3V. 7

8 Pin Configurations (continued) TOP VIEW PRESS: BiCMOS Chip Information Package Information For the latest package outline information and land patterns, go to PACKAGE TYPE PACKAGE CODE DUMT NO. 8 SO S TDFN-EP T TDFN 8

9 REVISION NUMBER REVISION DATE DESCRIPTION Revision History PAGES CHANGED 3 4/9 Fixed typo in UL # 1 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, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.