19-1865; Rev 0; 11/00 Dual USB Switch with Fault Blanking Features ♦ Dual USB Switch in Tiny 10-Pin µMAX Package The MAX1812 has multiple 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 current-limiting circuitry to protect the input supply against both overload and short-circuit conditions. Independent fault signals (FAULTA and FAULTB) notify the microprocessor when a thermal-overload, current limit, undervoltage lockout, or short-circuit fault occurs. A 20ms fault-blanking feature enables the circuit to ignore momentary faults, such as those caused when hot-swapping a capacitive load, thereby preventing false alarms to the host system. The MAX1812 is available in a space-saving 10-pin µMAX package. For single versions of this device, refer to the MAX1693, MAX1694, and MAX1607 data sheets. ♦ +4.0V to +5.5V Input Voltage Range ♦ Guaranteed 500mA Load per Channel ♦ Built-In 20ms Fault Blanking ♦ Compliant to USB Specifications ♦ 45µA Quiescent Current ♦ 3µA Shutdown Current ♦ Independent Shutdown Control ♦ Independent FAULT Indicator Outputs ♦ Thermal-Overload Protection ♦ UL Listing Pending ________________________Applications USB Ports Ordering Information PART USB Hubs MAX1812EUB TEMP. RANGE PIN-PACKAGE -40°C to +85°C 10 µMAX Notebook Computers Desktop Computers PDAs and Palmtop Computers Docking Stations Typical Operating Circuit OUTA INA USB PORT A Pin Configuration TOP VIEW IN INPUT 4.0V TO 5.5V INB ONA 1 MAX1812 FAULTA OUTB FAULTB ONA ONB ONA ONB GND USB PORT B INA 2 IN 3 INB ONB 10 FAULTA 9 OUTA 8 GND 4 7 OUTB 5 6 FAULTB MAX1812 µMAX ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX1812 General Description The MAX1812 is a dual current-limited switch specifically made for USB applications. Each channel is guaranteed to supply 500mA and meets USB specifications. The MAX1812’s low quiescent supply current (45µA) and shutdown current (3µA) conserve battery power in portable applications. MAX1812 Dual USB Switch with Fault Blanking ABSOLUTE MAXIMUM RATINGS IN, INA, INB, ONA, ONB, OUTA, OUTB to GND......-0.3V to +6V FAULTA, FAULTB to GND .........................-0.3V to (VIN_ + 0.3V) INA, IN to OUTA; INB, IN to OUTB..........................-0.3V to +6V OUTA, OUTB Maximum Continuous Switch Current (per channel, internally limited) .........................................1.2A FAULTA, FAULTB Current .................................................20mA Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ............444mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°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 (VIN = VINA = VINB = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C) (Note 1) PARAMETER SYMBOL CONDITIONS Supply Voltage Range Switch On-Resistance MIN TYP 4.0 RON Standby Supply Current Quiescent Supply Current TA = +25°C, each switch 75 TA = -40°C to +85°C, each switch UVLO Short-Circuit Current Limit 2 105 10 µA Both switches enabled, IOUTA = IOUTB = 0 45 100 µA 0.002 1 µA Rising edge, 3% hysteresis 10 3.0 3.4 3.8 500 ILIM ISHORT mΩ 3 Continuous Load Current Continuous Current Limit V Both switches disabled Switches disabled, VOUTA = VOUTB = 0, TA = -40°C to 85°C Undervoltage Lockout Threshold UNITS 5.5 135 Switches disabled, VOUTA = VOUTB = 0, TA = +25°C OUT_ Leakage Current MAX VIN_ - VOUT_ = 0.5V VOUT_ = 0 (IOUT pulsing) V mA 0.6 0.9 1.2 A 0.8 1.2 1.6 A(peak) 0.35 ARMS 1 V Short-Circuit Detect Threshold (Note 2) Continuous Current-Limit Blanking Timeout Period From continuous current-limit condition to FAULT_ assertion 10 20 35 ms Short-Circuit Blanking Timeout Period From short-circuit current-limit condition to FAULT_ assertion 7.5 18 35 ms Turn-On Delay ROUT = 10Ω, COUT = 1µF does not include rise time (from ON_ to 10% of VOUT) 0.5 1.2 4.0 ms Output Rise Time ROUT = 10Ω, COUT = 1µF, from 10% to 90% of VOUT 2.5 Turn-Off Delay from ON ROUT = 10Ω, COUT = 1µF does not include fall time (from ON_ to 90% of VOUT) 0.8 Output Fall Time COUT = 1µF, ROUT = 10Ω, from 90% to 10% of VOUT 2.5 ms Thermal Shutdown Threshold 15°C hysteresis 160 °C _______________________________________________________________________________________ ms 3 ms Dual USB Switch with Fault Blanking (VIN = VINA = VINB = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS Logic Input High Voltage VIN_ = +4V to +5.5V Logic Input Low Voltage VIN_ = +4V to +5.5V MIN TYP MAX UNITS 2 V 0.8 V Logic Input Current V ON_ = 0 or VIN_ 1 µA FAULT_ Output Low Voltage ISINK = 1mA, VIN_ = 4V 0.4 V FAULT_ Output High Leakage Current VIN_ = V FAULT_ = 5.5V 1 µA -1 Note 1: Specifications to -40°C are guaranteed by design, not production tested. Note 2: The output voltage at which the device transitions from short-circuit current limit to continuous current limit. Typical Operating Characteristics (VIN = VINA = VINB = 5V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) 75 50 25 VIN = 5.5V 50 VIN = 5V 45 VIN = 4.5V 40 0 0 1 2 3 4 INPUT VOLTAGE (V) 5 6 5 SHUTDOWN SUPPLY CURRENT (µA) QUIESCENT CURRENT (µA) VONA = VONB = 0V MAX1812 toc02 55 MAX1812 toc01 100 QUIESCENT CURRENT (µA) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE QUIESCENT CURRENT vs. TEMPERATURE MAX1812 toc03 QUIESCENT CURRENT vs. INPUT VOLTAGE VONA = VONB = VIN 4 3 2 1 0 -40 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX1812 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = VINA = VINB = 5V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) VONA = VONB = 0V 1.25 NORMALIZED RON 100 10 1.00 0.75 1 900 VIN = 5V 890 CONTINUOUS CURRENT LIMIT (mA) MAX 1812 toc05 VONA = VONB = VIN LEAKAGE CURRENT (nA) 1.50 MAX1812 toc04 1000 CONTINUOUS CURRENT LIMIT vs. TEMPERATURE NORMALIZED RON vs. TEMPERATURE MAX1812 toc06 OUT_ LEAKAGE CURRENT vs. TEMPERATURE 880 870 860 850 840 830 820 810 0.1 -15 10 35 60 85 -15 10 35 60 -40 85 35 60 TOTAL TURN-ON TIME vs. TEMPERATURE TOTAL TURN-OFF TIME vs. TEMPERATURE FAULT-BLANKING TIME vs. TEMPERATURE 3.4 3.3 VIN = 5.5V 3.4 VIN = 5.5V 3.3 3.2 VIN = 5V 3.1 3.0 2.9 VIN = 4.5V 2.8 3.2 TOTAL TURN-ON TIME = RISE TIME + DELAY TIME 2.7 -15 10 35 60 -15 10 35 60 FAULT OUTPUT LOW VOLTAGE vs. TEMPERATURE OVERLOAD RESPONSE INTO 2.5Ω LOAD 20.5 -40 0 VIN = 4.5V 10 35 60 5V A B 0 FAULT RECOVERS 0.175 C C 0 0.150 0 LOAD REMOVED VIN = 5.5V D 0.125 0 D 0 0.100 -40 -15 10 35 TEMPERATURE (°C) 4 85 MAX1812-12 5V A B 0.200 -15 OVERLOAD RESPONSE INTO 2.5Ω LOAD (EXPANDED TIME SCALE) MAX1812-11 MAX1812 toc10 VIN = 5V 21.0 TEMPERATURE (°C) TEMPERATURE (°C) 0.225 21.5 85 TEMPERATURE (°C) 0.250 VIN = 5.0V 20.0 -40 85 22.0 TOTAL TURN-OFF TIME = FALL TIME + DELAY TIME 2.6 3.0 85 MAX1812 toc09 MAX1812 toc08 3.5 FAULT-BLANKING TIME (ms) VIN = 5V 3.5 3.6 TOTAL TURN-OFF TIME (ms) MAX1812 toc07 VIN = 4.5V 3.7 -40 10 TEMPERATURE (°C) 3.8 3.1 -15 TEMPERATURE (°C) 3.9 3.6 -40 TEMPERATURE (°C) 4.0 TOTAL TURN-ON TIME (ms) 800 0.50 -40 FAULT OUTPUT LOW VOLTAGE (V) MAX1812 Dual USB Switch with Fault Blanking 60 85 A : VIN, 5V/div B : VOUTA, 5V/div 5ms/div C : VFAULTA, 5V/div D : IOUTA, 1A/div A : VIN, 5V/div B : VOUTA, 5V/div 500µs/div C : V FAULTA, 5V/div D : IOUTA, 1A/div _______________________________________________________________________________________ Dual USB Switch with Fault Blanking (VIN = VINA = VINB = 5V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) SHORT-CIRCUIT RESPONSE INTO 0Ω LOAD (EXPANDED TIME SCALE) SHORT-CIRCUIT RESPONSE INTO 0Ω MAX1812-13 A SWITCH TURN-ON TIME MAX1812-14 A 5V 5V MAX1812-15 A 0 B B 0 0 C C 0 0 FAULT RECOVERS B LOAD REMOVED RL = 10Ω COUT = 1µF D D 0 10ms/div C : V FAULTA, 5V/div D : IOUTA, 1A/div A : VIN, 1V B : VOUTA, 5V/div 0 A : VIN, 1V/div B : VOUTA, 5V/div 1ms/div 400µs/div C : V FAULTA, 5V/div D : IOUTA, 1A/div A : VONA, 5V/div B : VOUTA, 1V/div STARTUP TIME (TYPICAL USB APPLICATION) SWITCH TURN-OFF TIME MAX1812-17 MAX1812-16 RL = 10Ω COUT = 1µF A 0 0 A 0 B 0 B RL = 10Ω COUT = 150µF 0 0 C 0 1ms/div A : V ONA, 5V/div B : VOUTA, 1V/div 500µs/div C : VOUTA, 2V/div A : VONA, 5V/div B : VFAULTA, 5V/div D : IOUTA, 0.5A/div _______________________________________________________________________________________ 5 MAX1812 Typical Operating Characteristics (continued) Dual USB Switch with Fault Blanking MAX1812 Pin Description PIN NAME FUNCTION 1 ONA 2, 3, 4 INA, IN, INB Power Input. Connect all IN_ pins together and bypass with a 0.1µF capacitor to ground. Load conditions may require additional bulk capacitance to prevent the input from being pulled down. 5 ONB Control Input for Switch B. Can be higher than IN_ without damage. A logic low turns switch B on. 6 FAULTB Fault Indicator Output for Switch B. This open-drain output goes low when switch B is in thermal shutdown or undervoltage lockout or in a sustained (>20ms) current-limit or short-circuit condition. 7 OUTB Power Output for Switch B. Connect a 1µF capacitor from OUTB to ground. Load condition may require additional bulk capacitance. See USB requirements. 8 GND Ground 9 OUTA Power Output for Switch A. Connect a 1µF capacitor from OUTA to ground. Load condition may require additional bulk capacitance. See USB requirements. 10 FAULTA Control Input for Switch A. Can be driven higher than IN_ without damage. A logic low turns switch A on. Fault Indicator Output for Switch A. This open-drain output goes low when switch A is in thermal shutdown or undervoltage lockout or in a sustained (>20ms) current-limit or short-circuit condition. Detailed Description The MAX1812 is a dual current-limited switch designed specifically for USB applications. It has two independent switches, each with its own enable control input. Each switch also has an independent error flag output to notify the USB controller when the current-limit, shortcircuit, undervoltage-lockout, or thermal-shutdown threshold is reached (Figure 1). The MAX1812 operates from a +4V to +5.5V input voltage and guarantees a minimum output current of 500mA. A built-in current-limit of 0.9A (typ) limits the current in the event of a heavy overload condition. The MAX1812 has independent thermal shutdown for each switch in the event of a prolonged overload or short-circuit condition. Use of internal low RON NMOS switches enables the MAX1812 to fit two switches in the ultra-small 10-pin µMAX package. An internal micropower charge pump generates the high-side supply needed for driving the gates of these high-side switches. Separate currentlimiting and thermal-shutdown circuits permit each switch to operate independently, improving system robustness. Undervoltage Lockout and Input Voltage Requirements The MAX1812 includes an undervoltage-lockout (UVLO) circuit to prevent erroneous switch operation when the input voltage goes low during startups and 6 brownout conditions. Operation is inhibited when VIN_ < 3.4V. Output Fault Protection The MAX1812 senses the switch output voltage and selects continuous current limiting when VOUT_ > 1V, or pulsed current limiting when VOUT_ < 1V. When VOUT_ > 1V, the device operates in a continuous current-limit mode, which sets the output current limit to 0.9A (typ). When VOUT_ < 1V, the device operates in short-circuit current-limit mode. The MAX1812 pulses the output current at 400Hz to limit the output current to 0.35A (RMS). Thermal Shutdown The MAX1812 features independent thermal shutdown for each switch channel, allowing one switch to deliver power even if the other switch has a fault condition. When the junction temperature exceeds +160°C, the switch turns off and the FAULT_ output goes low immediately; fault blanking does not occur during thermal limit. When the junction cools by 15°C, the switch turns back on again. If the fault overload condition continues, the switch will cycle on and off, resulting in a pulsed output that saves battery power. Fault Indicators The MAX1812 provides an open-drain fault output (FAULT_) for each switch. For most applications, connect FAULT_ to IN_ through a 100kΩ pullup resistor. _______________________________________________________________________________________ Dual USB Switch with Fault Blanking MAX1812 IN_ FAULTA ONA 4-MOS Q-PMP ILIM BIAS OUTA 1µF UVLO THERMAL SHUTDOWN FAULT LOGIC GND REF 4.0V TO 5.5V IN_ OSC 25kHz 0.1µF TIMER 20ms OUTB 1µF ILIM 4-MOS Q-PMP ONB IN_ MAX1812 FAULTB Figure 1. Functional Diagram FAULT_ goes low when any of the following conditions occur: • The input voltage is below the undervoltage-lockout (UVLO) threshold. • The switch junction temperature exceeds the thermal shutdown temperature limit of +160°C. • The switch is in current limit or short-circuit limit mode and the fault-blanking period is exceeded. The fault indicators have a latching delay to prevent short FAULT_ pulses. After the fault-condition is removed, the FAULT_ output will deassert after a 20ms delay. Ensure that the MAX1812 has adequate input bypass capacitance to prevent glitches from triggering FAULT_ outputs. Input glitches greater than 0.2V/µS may cause spurious FAULT_ transitions. _______________________________________________________________________________________ 7 MAX1812 Dual USB Switch with Fault Blanking Table 1. MAX1812 Current Limiting and Fault Behavior CONDITION If a short circuit is present (VOUT < 1V) MAX1812 BEHAVIOR If a short circuit is present at startup, current will ramp up to ISHORT in 2ms–3ms, and the switch will shut off. The blanking timer turns on, but FAULT_ stays high. If a short circuit occurs during operation, current output will be pulsed at 0.35A (RMS). If ISHORT is exceeded between 15ms–20ms, then the short circuit is still present and FAULT_ goes low at 20ms. When the short circuit is removed, the next ramped current pulse will soft-start the output. The FAULT_ flag releases at the end of the next cycle. If an overload current is present (VOUT > 1V) Current will regulate at ILIM (0.9A typ). The blanking timer turns on, but FAULT_ stays high. Continuous current at ILIM persists until the overload is removed or a thermal fault occurs. If overcurrent is still present at 20ms, then FAULT_ goes low. When the overcurrent condition is removed, the FAULT_ flag releases at the end of the next cycle. If thermal fault condition is present FAULT_ immediately goes low (the blanking timer does not apply to thermal faults), and the switch turns off. When thermal condition is removed, switch control returns to the current-limit loop. FAULT_ goes high at the end of the timer period if no further thermal or current-limit faults exist. Behavior During Current Limit and Fault Blanking The MAX1812 limits switch current in three ways (Table 1). When ON_ is high, the switch is off, and the residual output current is dominated by leakage. When ON_ is low, the switch can supply a continuous output current of at least 500mA. When the output current exceeds the 0.9A (typ) threshold, the MAX1812 will limit the current, depending upon the output voltage. If VOUT_ > 1V (current-limit mode), the MAX1812 serves the switch drive so that the peak current does not exceed 1.2A (max). If VOUT_ < 1V (short-circuit mode), the MAX1812 pulses the switch drive to decrease the current to 0.35A (RMS). Note that a thermal overload may result from either of these high-current conditions. The switches in the MAX1812 may enter current limit in normal operation when powering up or when driving heavy capacitive loads. To differentiate these conditions from short circuits or sustained overloads that may damage the device, the MAX1812 has an independent fault-blanking circuit in each switch. When a load transient causes the device to enter current limit, an internal counter monitors the duration of the fault. If the load fault persists beyond the 20ms fault-blanking timeout, then the switch turns off and the FAULT_ signal asserts low. Only current-limit and short-circuit faults are blanked. Thermal overload faults and input voltage 8 drops below the UVLO threshold immediately cause the switch to turn off and the FAULT_ to assert low. Fault blanking allows the MAX1812 to handle USB loads that may not be fully compliant with the USB specifications. USB loads with additional bypass capacitance and/or large startup currents can be successfully powered even while protecting the upstream power source. If the switch is able to bring up the load within the 20ms blanking period, no fault is reported. Applications Information Input Power Source The power for all control and charge-pump circuitry comes from IN, INA, and INB. All three IN_ pins must be connected together externally. Input Capacitor To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from IN_ to ground. A 0.1µF ceramic capacitor is required for local decoupling; however, higher capacitor values will further reduce the voltage drop at the input (Figure 2). When driving inductive loads, a larger capacitance will prevent voltage spikes from exceeding the device’s absolute maximum ratings. Output Capacitor An output capacitor helps prevent inductive parasitics from pulling OUT_ negative during turn-off. At startups, _______________________________________________________________________________________ Dual USB Switch with Fault Blanking USB PORT A power device will turn off rapidly (100ns typ) to protect the power device. Layout and Thermal Dissipation IN INPUT 4.0V TO 5.5V INB MAX1812 FAULTA OUTB USB PORT B FAULTB ONA ONB ONA ONB GND Figure 2. Typical Application Circuit the switch pulses the output current at 0.35A RMS until the output voltage rises above 1V, then the capacitor will continue to charge at the full 0.9A current limit. There is no limit to the output capacitor size, but to prevent a startup fault assertion the capacitor must charge up within the fault-blanking delay period. Typically starting up into a 330µF or smaller capacitor will not trigger a fault output. In addition to bulk capacitance, small value (0.1µF) ceramic capacitors improve the output’s resilience to electrostatic discharge (ESD). 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 can cause the output voltage at the USB port to ring during a load step. The MAX1812 is capable of driving inductive loads, but care should be taken to avoid exceeding the device’s absolute maximum ratings. Usually, the load inductance is relatively small, and the MAX1812’s input includes a substantial bulk capacitance from an upstream regulator as well as a local bypass, so the amount of transient overshoot is small. If the load inductance is very large, ringing may become severe, and it may be necessary to clamp the MAX1812’s output below 6V and above -0.3V. Turn-On and Turn-Off Behavior In normal operation, the MAX1812’s internal switches turn on and turn off slowly under the control of the ON_ inputs. Transition times for both edges are approximately 2ms. The slow charge-pump switch-drive minimizes load transients the upstream power source. Under thermal fault and under voltage lockout, the To optimize the switch-response time to output shortcircuit conditions, it is important to keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors no more than 5mm from the package leads. All IN_ and OUT_ pins must be connected with short traces to the power bus. Wide power bus planes provide superior heat dissipation through the switch IN_ and OUT_ pins. Under normal operating conditions, power dissipation is small and the package can conduct heat away. Calculate the maximum power dissipation for normal operation as follows: P= (0.5A)2 P = (IOUT_)2 RON x 0.135Ω = 34mW per switch where IOUT_ is the maximum normal operating current, and RON is the on-resistance of the switch (135mΩ max). The worst-case power dissipation occurs when the switch is in current limit and the output is greater than 1V. In this case, the power dissipated in each switch is the voltage drop across the switch multiplied by the current limit: P = (ILIM) (VIN - VOUT) For a 5V input and 1V output, the maximum power dissipation per switch is: P = (1.2A) ( 5V - 1V) = 4.8W Since the maximum package power dissipation is only 444mW, the MAX1812 die temperature will quickly exceed the thermal-shutdown threshold, and the switch output will pulse on and off. The duty cycle and period are strong functions of the ambient temperature and the PC board layout. When the output is short circuited, current limiting activates and the power dissipated across the switch increases as does junction temperature. If the fault condition persists, the thermal-overload-protection circuitry activates (see Thermal Shutdown). Chip Information TRANSISTOR COUNT: 2739 PROCESS: BiCMOS _______________________________________________________________________________________ 9 MAX1812 OUTA INA Dual USB Switch with Fault Blanking 10LUMAX.EPS MAX1812 Package Information 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.