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19-1865; Rev 0; 11/00
Dual USB Switch with Fault Blanking
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 (45A) and shutdown current (3A) conserve battery power in portable applications. 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 MAX package. For single versions of this device, refer to the MAX1693, MAX1694, and MAX1607 data sheets.
Features
o Dual USB Switch in Tiny 10-Pin MAX Package o Guaranteed 500mA Load per Channel o Built-In 20ms Fault Blanking o Compliant to USB Specifications o +4.0V to +5.5V Input Voltage Range o 45A Quiescent Current o 3A Shutdown Current o Independent Shutdown Control o Independent FAULT Indicator Outputs o Thermal-Overload Protection o UL Listing Pending
MAX1812
________________________Applications
USB Ports USB Hubs Notebook Computers Desktop Computers PDAs and Palmtop Computers Docking Stations
PART MAX1812EUB
Ordering Information
TEMP. RANGE -40C to +85C PIN-PACKAGE 10 MAX
Typical Operating Circuit
INA IN OUTA
Pin Configuration
TOP VIEW
USB PORT A
INPUT 4.0V TO 5.5V
INB
ONA 1
10 FAULTA 9 OUTA GND OUTB FAULTB
MAX1812
FAULTA FAULTB ONA ONB ONA ONB OUTB
INA
USB PORT B
2 3 4 5
IN INB ONB
MAX1812
8 7 6
GND
MAX
________________________________________________________________ Maxim Integrated Products
1
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Dual USB Switch with Fault Blanking MAX1812
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 = +70C) 10-Pin MAX (derate 5.6mW/C above +70C) ............444mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C) (Note 1)
PARAMETER Supply Voltage Range Switch On-Resistance Standby Supply Current Quiescent Supply Current RON TA = +25C, each switch TA = -40C to +85C, each switch Both switches disabled Both switches enabled, IOUTA = IOUTB = 0 Switches disabled, VOUTA = VOUTB = 0, TA = +25C Switches disabled, VOUTA = VOUTB = 0, TA = -40C to 85C Undervoltage Lockout Threshold Continuous Load Current Continuous Current Limit Short-Circuit Current Limit Short-Circuit Detect Threshold Continuous Current-Limit Blanking Timeout Period Short-Circuit Blanking Timeout Period Turn-On Delay Output Rise Time Turn-Off Delay from ON Output Fall Time Thermal Shutdown Threshold ILIM ISHORT VIN_ - VOUT_ = 0.5V VOUT_ = 0 (IOUT pulsing) (Note 2) From continuous current-limit condition to FAULT_ assertion From short-circuit current-limit condition to FAULT_ assertion ROUT = 10, COUT = 1F does not include rise time (from ON_ to 10% of VOUT) ROUT = 10, COUT = 1F, from 10% to 90% of VOUT ROUT = 10, COUT = 1F does not include fall time (from ON_ to 90% of VOUT) COUT = 1F, ROUT = 10, from 90% to 10% of VOUT 15C hysteresis 10 7.5 0.5 UVLO Rising edge, 3% hysteresis 3.0 500 0.6 0.8 0.9 1.2 0.35 1 20 18 1.2 2.5 0.8 2.5 160 3 35 35 4.0 1.2 1.6 3.4 3 45 0.002 SYMBOL CONDITIONS MIN 4.0 75 TYP MAX 5.5 105 135 10 100 1 A 10 3.8 V mA A A(peak) ARMS V ms ms ms ms ms ms C UNITS V m A A
OUT_ Leakage Current
2
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Dual USB Switch with Fault Blanking
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VINA = VINB = 5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Logic Input High Voltage Logic Input Low Voltage Logic Input Current FAULT_ Output Low Voltage FAULT_ Output High Leakage Current SYMBOL CONDITIONS VIN_ = +4V to +5.5V VIN_ = +4V to +5.5V V ON_ = 0 or VIN_ ISINK = 1mA, VIN_ = 4V VIN_ = V FAULT_ = 5.5V -1 MIN 2 0.8 1 0.4 1 TYP MAX UNITS V V A V A
MAX1812
Note 1: Specifications to -40C 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 = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX1812 toc01
QUIESCENT CURRENT vs. TEMPERATURE
MAX1812 toc02
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
VONA = VONB = VIN 4
MAX1812 toc03
100 VONA = VONB = 0V QUIESCENT CURRENT (A) 75
55 VIN = 5.5V 50 VIN = 5V
5 SHUTDOWN SUPPLY CURRENT (A)
QUIESCENT CURRENT (A)
3
50
2
45 VIN = 4.5V
25
1
0 0 1 2 3 4 5 6 INPUT VOLTAGE (V)
40 -40 -15 10 35 60 85 TEMPERATURE (C)
0 -40 -15 10 35 60 85 TEMPERATURE (C)
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Dual USB Switch with Fault Blanking MAX1812
Typical Operating Characteristics
(VIN = VINA = VINB = 5V, Circuit of Figure 2, TA = +25C, unless otherwise noted.)
OUT_ LEAKAGE CURRENT vs. TEMPERATURE
MAX1812 toc04
NORMALIZED RON vs. TEMPERATURE
MAX 1812 toc05
CONTINUOUS CURRENT LIMIT vs. TEMPERATURE
890 CONTINUOUS CURRENT LIMIT (mA) 880 870 860 850 840 830 820 810 VIN = 5V
MAX1812 toc06
1000 VONA = VONB = VIN LEAKAGE CURRENT (nA) 100
1.50 VONA = VONB = 0V 1.25 NORMALIZED RON
900
10
1.00
0.75 1 0.1 -40 -15 10 35 60 85 TEMPERATURE (C)
0.50 -40 -15 10 35 60 85 TEMPERATURE (C)
800 -40 -15 10 35 60 85 TEMPERATURE (C)
TOTAL TURN-ON TIME vs. TEMPERATURE
MAX1812 toc07
TOTAL TURN-OFF TIME vs. TEMPERATURE
MAX1812 toc08
FAULT-BLANKING TIME vs. TEMPERATURE
VIN = 5.0V FAULT-BLANKING TIME (ms) 21.5
MAX1812 toc09
4.0 3.9 TOTAL TURN-ON TIME (ms) 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 -40 -15 10 35 60 TOTAL TURN-ON TIME = RISE TIME + DELAY TIME VIN = 5.5V VIN = 5V VIN = 4.5V
3.6 3.5 TOTAL TURN-OFF TIME (ms) 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 2.6 TOTAL TURN-OFF TIME = FALL TIME + DELAY TIME VIN = 4.5V VIN = 5V VIN = 5.5V
22.0
21.0
20.5
20.0 -40 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
85
TEMPERATURE (C)
FAULT OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX1812 toc10
OVERLOAD RESPONSE INTO 2.5 LOAD
MAX1812-11
OVERLOAD RESPONSE INTO 2.5 LOAD (EXPANDED TIME SCALE)
MAX1812-12
0.250 FAULT OUTPUT LOW VOLTAGE (V) 0.225 0.200 VIN = 4.5V 0.175 0.150 0.125 0.100 -40 -15 10 35 60 VIN = 5V
A
5V
A
5V
B FAULT RECOVERS C
0
B C
0
0 VIN = 5.5V D 0 5ms/div C : VFAULTA, 5V/div D : IOUTA, 1A/div D LOAD REMOVED
0
0
85 A : VIN, 5V/div B : VOUTA, 5V/div
TEMPERATURE (C)
A : VIN, 5V/div B : VOUTA, 5V/div
500s/div C : V FAULTA, 5V/div D : IOUTA, 1A/div
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Dual USB Switch with Fault Blanking MAX1812
Typical Operating Characteristics (continued)
(VIN = VINA = VINB = 5V, Circuit of Figure 2, TA = +25C, unless otherwise noted.)
SHORT-CIRCUIT RESPONSE INTO 0
MAX1812-13
SHORT-CIRCUIT RESPONSE INTO 0 LOAD (EXPANDED TIME SCALE)
5V A B 0 C 0
MAX1812-14
SWITCH TURN-ON TIME
5V A
MAX1812-15
A B
0
C 0 FAULT RECOVERS 0 B
LOAD REMOVED D A : VIN, 1V B : VOUTA, 5V/div 10ms/div C : V FAULTA, 5V/div D : IOUTA, 1A/div 0 D A : VIN, 1V/div B : VOUTA, 5V/div 400s/div C : V FAULTA, 5V/div D : IOUTA, 1A/div 0 1ms/div A : VONA, 5V/div B : VOUTA, 1V/div
RL = 10 COUT = 1F
0
SWITCH TURN-OFF TIME
MAX1812-16
STARTUP TIME (TYPICAL USB APPLICATION)
MAX1812-17
A
RL = 10 COUT = 1F
0 A B 0 0
B
RL = 10 COUT = 150F
0 1ms/div A : V ONA, 5V/div B : VOUTA, 1V/div
C 500s/div C : VOUTA, 2V/div A : VONA, 5V/div B : VFAULTA, 5V/div D : IOUTA, 0.5A/div
0 0
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Dual USB Switch with Fault Blanking MAX1812
Pin Description
PIN 1 2, 3, 4 5 6 7 8 9 10 NAME ONA INA, IN, INB ONB FAULTB OUTB GND OUTA FAULTA FUNCTION Control Input for Switch A. Can be driven higher than IN_ without damage. A logic low turns switch A on. Power Input. Connect all IN_ pins together and bypass with a 0.1F capacitor to ground. Load conditions may require additional bulk capacitance to prevent the input from being pulled down. Control Input for Switch B. Can be higher than IN_ without damage. A logic low turns switch B on. 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. Power Output for Switch B. Connect a 1F capacitor from OUTB to ground. Load condition may require additional bulk capacitance. See USB requirements. Ground Power Output for Switch A. Connect a 1F capacitor from OUTA to ground. Load condition may require additional bulk capacitance. See USB requirements. 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 MAX 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.
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 +160C, the switch turns off and the FAULT_ output goes low immediately; fault blanking does not occur during thermal limit. When the junction cools by 15C, 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.
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
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Fault Indicators
The MAX1812 provides an open-drain fault output (FAULT_) for each switch. For most applications, connect FAULT_ to IN_ through a 100k pullup resistor.
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Dual USB Switch with Fault Blanking MAX1812
IN_
FAULTA
ONA
4-MOS Q-PMP ILIM BIAS OUTA 1F THERMAL SHUTDOWN FAULT LOGIC REF GND
UVLO
4.0V TO 5.5V IN_ 0.1F OSC 25kHz TIMER 20ms OUTB ILIM 4-MOS Q-PMP 1F
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 +160C. * 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/S may cause spurious FAULT_ transitions.
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Dual USB Switch with Fault Blanking MAX1812
Table 1. MAX1812 Current Limiting and Fault Behavior
CONDITION 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. 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. 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.
If a short circuit is present (VOUT < 1V)
If an overload current is present (VOUT > 1V)
If thermal fault condition is present
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
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 0.1F 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,
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Dual USB Switch with Fault Blanking
power device will turn off rapidly (100ns typ) to protect the power device.
MAX1812
INA IN
OUTA
USB PORT A
Layout and Thermal Dissipation
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: (0.5A)2 P = (IOUT_)2 RON x 0.135 = 34mW per switch
INPUT 4.0V TO 5.5V
INB
MAX1812
FAULTA FAULTB ONA ONB ONA ONB OUTB
USB PORT B
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 330F or smaller capacitor will not trigger a fault output. In addition to bulk capacitance, small value (0.1F) ceramic capacitors improve the output's resilience to electrostatic discharge (ESD).
P=
where IOUT_ is the maximum normal operating current, and RON is the on-resistance of the switch (135m 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).
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
Chip Information
TRANSISTOR COUNT: 2739 PROCESS: BiCMOS
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Dual USB Switch with Fault Blanking MAX1812
Package Information
10LUMAX.EPS 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 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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