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19-1903; Rev 2; 10/02
Dual USB Switch with Fault Blanking and Autoreset
General Description
The MAX1823 is a dual, current-limited switch with autoreset specifically made for USB applications. The autoreset feature latches the switch off if the output is shorted, saving system power. The switch reactivates when the short-circuit condition is removed. Each channel is guaranteed to supply 720mA and meet USB specifications. The device's low quiescent supply current (50A) and standby current (3A) conserve battery power in portable applications. The MAX1823 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 (P) when a thermal-overload, current-limit, undervoltage lockout (UVLO), 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, preventing false alarms to the host system. The MAX1823 is available in a space-saving 10-pin MAX. The MAX1823 is enabled with an active-low signal and the MAX1823H is enabled with an active-high signal. For a dual switch without autoreset, refer to the MAX1812 data sheet. For single versions of this device, refer to the MAX1693, MAX1694, and MAX1607 data sheets. o Autoreset Feature Saves Power o Guaranteed 720mA Load per Channel o Built-In 20ms Fault Blanking o Compliant to USB Specification o 4V to 5.5V Input Voltage Range o Independent Shutdown Control (MAX1823--Active Low) (MAX1823H--Active High) o Independent FAULT Indicator Outputs o Thermal-Overload Protection o 50A Quiescent Current (Both Switches On) o 3A Standby Current o UL Listing Pending
Features
o Dual USB Switch in Tiny 10-Pin MAX Package
MAX1823/MAX1823H
Ordering Information
PART MAX1823EUB MAX1823HEUB TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 10 MAX 10 MAX
Applications
USB Ports and Hubs Notebook and Desktop Computers PDAs and Palmtop Computers Docking Stations
Typical Operating Circuit
INA IN INPUT 4V TO 5.5V INB OUTA USB PORT A
Pin Configuration
TOP VIEW
ONA 1
10 FAULTA 9 OUTA GND OUTB FAULTB
MAX1823
FAULTA FAULTB OUTB USB PORT B
INA IN INB ONB
2 3 4 5
MAX1823
8 7 6
ONA ONB
ONA ONB
GND
MAX
________________________________________________________________ Maxim Integrated Products
1
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
ABSOLUTE MAXIMUM RATINGS
IN, INA, INB, ONA, ONB, 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
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ONA = ONB = GND (MAX1823), ONA = ONB = IN (MAX1823H), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Supply Voltage Range Switch On-Resistance Standby Supply Current Quiescent Supply Current RON TA = +25 C, each switch TA = 0oC to +85oC, each switch ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) IOUTA = IOUTB = 0 IOUTA = IOUTB = 0 ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) VOUTA = VOUTB = 0, TA = +25oC OUT_ Off-Leakage Current ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) VOUTA = VOUTB = 0, TA = 0oC to +85oC VUVLO ILIM ISHORT Rising edge, 3% hysteresis VIN - VOUT_ = 0.5V VOUT_ = 0 (IOUT pulsing) VOUT_ = 0 (IOUT pulsing) (Note 1) From continuous current-limit condition to FAULT_ assertion From short-circuit current-limit condition to FAULT_ assertion ROUT_ = 10, does not include rise time (from ON_ (MAX1823) or ON_ (MAX1823H) asserted to VOUT = 10% VIN_) ROUT_ = 10, from 10% to 90% of VOUT_ ROUT_ = 10, does not include fall time (from ON_ (MAX1823) or ON_ (MAX1823H) deasserted to VOUT = 90% of VIN_) 10 7.5 3.0 720 0.72 0.8 0.90 1.2 0.35 1 20 18 35 35 1.20 1.6 3 40 50 0.02
o
SYMBOL
CONDITIONS
MIN 4.0
TYP 75
MAX 5.5 105 135 10 80 100 1.00
UNITS V m A A
A 0.02 3.4 10.00 3.8 V mA A A(peak) ARMS V ms ms
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
0.5
1.2 2.5 0.8
4.0
ms ms
3.0
ms
2
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Dual USB Switch with Fault Blanking and Autoreset
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ONA = ONB = GND (MAX1823), ONA = ONB = IN (MAX1823H), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Output Fall Time Thermal Shutdown Threshold Logic Input High Voltage Logic Input Low Voltage Logic Input Current FAULT_ Output Low Voltage FAULT_ Output High Leakage Current Autoreset OUT_ Current Autoreset Threshold Autoreset Blanking Time SYMBOL
o
MAX1823/MAX1823H
CONDITIONS ROUT_ = 10, from 10% to 90% of VOUT_ 15 C hysteresis VIN_ = 4V to 5.5V VIN_ = 4V to 5.5V ON_ = GND or IN_ (MAX1823), ON_ = GND or IN_ (MAX1823H) ISINK = 1mA, VIN_ = 4V VIN_ = VFAULT_ = 5.5V In latched-off state, VOUT_ = 0 In latched-off state, rising In latched-off state, VOUT_ > 0.5V
MIN
TYP 2.5 160
MAX
UNITS ms
o
C
2 0.8 -1 1 0.4 1 10 0.4 10 25 0.5 20 45 0.6 35
V V A V A mA V ms
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823), TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Supply Voltage Range Switch On-Resistance Standby Supply Current RON Each switch ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) IOUTA = IOUTB = 0 ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) IOUTA = IOUTB = 0 ON_ = IN_ (MAX1823), ON_ = GND (MAX1823H) VOUTA = VOUTB = 0 VUVLO ILIM ISHORT Rising edge, 3% hysteresis VIN_ - VOUT_ = 0.5V VOUT_ = 0 (IOUT pulsing) From continuous current-limit condition to FAULT_ assertion From short-circuit current-limit condition to FAULT_ assertion ROUT_ = 10, does not include rise time (from ON_ (MAX1823) or ON_ (MAX1823H) asserted to VOUT_ = 10% VIN_) 3.0 720 0.72 0.8 10 7.5 1.20 1.6 35 35.0 SYMBOL CONDITIONS MIN 4.0 TYP MAX 5.5 135 10 80 A 100 UNITS V m A
Quiescent Supply Current
OUT_ Off-Leakage Current Undervoltage Lockout Threshold Continuous Load Current Continuous Current Limit Current Limit into Short Circuit Continuous Current-Limit Blanking Timeout Period Short-Circuit Blanking Timeout Period Turn-On Delay
10 3.8
A V mA A APEAK ms ms
0.5
4.0
ms
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823) TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Turn-Off Delay from ON Logic Input High Voltage Logic Input Low Voltage Logic Input Current FAULT_ Output Low Voltage FAULT_ Output High Leakage Current Autoreset OUT_Current Autoreset Threshold Autoreset Blanking Time SYMBOL CONDITIONS ROUT_ = 10, does not include fall time (from ON_ (MAX1823) or ON_ (MAX1823H) deasserted to VOUT_ = 90% VIN_) VIN_= 4V to 5.5V VIN_= 4V to 5.5V VON_ = 0 or VIN_ ISINK = 1mA, VIN_ = 4V VIN_ = VFAULT_ = 5.5V In latched-off state, VOUT_ = 0 In latched-off state, rising In latched-off state, VOUT_ > 0.5V 10 0.4 10 -1 2 0.8 +1 0.4 1 50 0.6 35 MIN TYP MAX 3 UNITS ms V V A V A mA V ms
Note 1: The output voltage at which the device transitions from short-circuit current limit to continuous current limit. Note 2: Specifications to -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823), ON_ = IN_ (MAX1823H), TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX1823 toc01
QUIESCENT CURRENT vs. TEMPERATURE
MAX1823 toc02
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
ON_ = IN_ (MAX1823) ON_ = GND (MAX1823H) 3.3
MAX1823 toc03
60 54 QUIESCENT CURRENT (A) 48 42 36 30 24 18 12 6 0 0 1 2 3 4 5 6 INPUT VOLTAGE (V)
55 VIN_ = 5.5V
3.5 SHUTDOWN SUPPLY CURRENT (A)
QUIESCENT CURRENT (A)
53
51
VIN_ = 5V
3.1
49 VIN_ = 4.5V 47
2.9
2.7
45 -40 -15 10 35 60 85 TEMPERATURE (C)
2.5 -40 -15 10 35 60 85 TEMPERATURE (C)
4
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823), ON_ = IN_ (MAX1823H), TA = +25C, unless otherwise noted.)
SWITCH OFF-LEAKAGE vs. TEMPERATURE
MAX1823 toc04
NORMALIZED RON vs. TEMPERATURE
MAX 1823 toc05
CONTINUOUS CURRENT-LIMIT THRESHOLD vs. TEMPERATURE
MAX1823 toc06
1000
SWITCH OFF-LEAKAGE (nA)
100
CONTINUOUS CURRENT LIMIT (mA)
ON_ = IN_ (MAX1823) ON_ = GND (MAX1823H)
1.50
940
1.25 10 NORMALIZED RON
930
VIN_ = 5.5V
1.00
920
VIN_ = 5V VIN_ = 4.5V
1
0.1
0.75
910
0.01 -40 -15 10 35 60 85 TEMPERATURE (C)
0.50 -40 -15 10 35 60 85 TEMPERATURE (C)
900 -40 -15 10 35 60 85 TEMPERATURE (C)
TURN-ON TIME vs. TEMPERATURE
MAX1823 toc07
TURN-OFF TIME vs. TEMPERATURE
MAX1823 toc08
FAULT-BLANKING TIME vs. TEMPERATURE
MAX1823 toc09
4.0
3.5
22.0
TURN-OFF TIME (ms)
VIN_ = 4.5V
TURN-ON TIME (ms)
VIN_ = 5V 3.1
VIN_ = 5.5V
FAULT-BLANKING TIME (ms)
3.8
3.3
21.8 VIN_ = 4.5V
3.6 VIN_ = 5V 3.4
21.6
2.9
21.4
VIN_ = 5V VIN_ = 5.5V
3.2
VIN_ = 5.5V
2.7 VIN_ = 4.5V 2.5
21.2
3.0 -40 -15 10 35 60 85 TEMPERATURE (C)
21.0 -40 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
FAULT_ OUTPUT LOW VOLTAGE vs. TEMPERATURE
IFAULT_ = 1mA 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 85 TEMPERATURE (C) VIN_ = 5.5V VIN_ = 5V
MAX1823 toc10
AUTORESET CURRENT vs. TEMPERATURE
MAX1823 toc11
AUTORESET CURRENT vs. INPUT VOLTAGE
TA = -40C AUTORESET CURRENT (mA) 40 TA = +25C 30
MAX1823 toc12
0.250
40 VIN_ = 5.5V
50
AUTORESET CURRENT (mA)
35
30
25
20 TA = +85C 10
20 VIN_ = 4.5V 15 -40 -15 10 35 60 85 TEMPERATURE (C) VIN_ = 5V
0 3.6 4.4 5.2 6.0 INPUT VOLTAGE (V)
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5
Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823), ON_ = IN_ (MAX1823H), TA = +25C, unless otherwise noted.)
OVERLOAD RESPONSE INTO 2.5 (EXPANDED TIME SCALE)
MAX1823 toc14
OVERLOAD RESPONSE INTO 2.5
MAX1823 toc13
SHORT-CIRCUIT RESPONSE INTO 0
MAX1823 toc15
A
5V
A B
5V
A B
5V
B
0 C
0
0
C
C 0 D 0 0
D
0 10ms/div C: VFAULTA, 5V/div D: IOUTA, 1A/div 500s/div C: VFAULTA, 5V/div D: IOUTA, 1A/div
0
D
0 10ms/div C: VFAULTA, 5V/div D: IOUTA, 1A/div
A: B:
VIN_, 5V/div VOUTA, 5V/div
A: VIN_, 5V/div B: VOUTA, 5V/div
A: VIN_, 5V/div B: VOUTA, 5V/div
SHORT-CIRCUIT RESPONSE INTO 0 (EXPANDED TIME SCALE)
MAX1823 toc16
SWITCH TURN-ON TIME (MAX1823)
MAX1823 toc17
A
5V
A 0
B C
0 5V
B D 0 0 1ms/div
A: VIN_, 5V/div B: VOUTA, 5V/div
500s/div C: VFAULTA, 5V/div D: IOUTA, 2A/div
A: VONA, 5V/div B: VOUTA, 2V/div
6
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823), ON_ = IN_ (MAX1823H), TA = +25C, unless otherwise noted.)
STARTUP TIME (TYPICAL USB APPLICATION)
MAX1823 toc19
SWITCH TURN-OFF TIME
MAX1823 toc18
A A 0 B
0 5V
C 0 B 0 1ms/div A: VONA, 5V/div B: VOUTA, 2V/div A: VONA, 5V/div B: VFAULTA, 5V/div D 0
500s/div C: VOUTA, 2V/div D : IOUTA, 0.5A/div
Pin Description
PIN 1 2, 3, 4 5 6 7 8 9 10 NAME ONA *(ONA) INA, IN, INB ONB *(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 for the MAX1823, and a logic high turns switch A on for the MAX1823H. 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 driven higher than IN_ without damage. A logic low turns switch B on for the MAX1823, and a logic high turns switch B on for the MAX1823H. Fault Indicator Output for Switch B. This open-drain output goes low when switch B is in thermal shutdown or UVLO 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. Ground Power Output for Switch A. Connect a 1F capacitor from OUTA to ground. Load condition may require additional bulk capacitance. Fault Indicator Output for Switch A. This open-drain output goes low when switch A is in thermal shutdown or UVLO or in a sustained (>20ms) current-limit or short-circuit condition.
*() are for MAX1823H only
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7
Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
Detailed Description
The MAX1823 is a dual current-limited switch designed for USB applications. It has two independent switches, each with its own enable control input and autoreset function. Each switch has an error-flag output to notify the USB controller when the current limit, short circuit, undervoltage lockout, or thermal shutdown threshold is reached (Figure 2.) The MAX1823 operates from a 4V to 5.5V input voltage range and guarantees a minimum 720mA output current. A built-in 0.9A current limit limits the current in the event of a heavy overload condition. The MAX1823 has independent thermal shutdown for each switch in the event of a prolonged overload or short-circuit condition. The autoreset function monitors the overload and automatically turns the switch on when the overload is removed. Use of low RON NMOS switches enables the MAX1823 to provide 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 current limiting and thermal shutdown circuits permit each switch to operate independently, improving system robustness. can also be reset from fault manually by toggling ON_ (ON_ for MAX1823H) for that channel.
Thermal Shutdown
The MAX1823 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 on again. If the fault overload condition continues, the switch cycles on and off, resulting in a pulsed output, saving battery power.
Fault Indicators
The MAX1823 provides an open-drain fault output (FAULT_) for each switch. For most applications, connect FAULT_ to IN_ through a 100k pullup resistor. FAULT_ goes low when any of the following conditions occur: * The input voltage is below the UVLO threshold. * The switch junction temperature exceeds the +160C thermal shutdown temperature limit. * The switch is in current-limit or short-circuit limit mode after the fault-blanking period is exceeded. * The switch is in autoreset mode. After the fault condition is removed, the FAULT_ output deasserts after a 20ms delay. Ensure that the MAX1823 has adequate input bypass capacitance to prevent glitches from triggering FAULT_ outputs. Input glitches greater than 0.2V/s may cause erroneous FAULT_ indications.
Undervoltage Lockout and Input Voltage Requirements
The MAX1823 includes a UVLO circuit to prevent erroneous switch operation when the input voltage goes low during startup and brown-out conditions. Operation is inhibited when VIN_ is less than 3.4V.
Output Fault Protection
The MAX1823 senses the switch output voltage and selects continuous current limiting when V OUT is greater than 1V or short-circuit current limiting when VOUT is less than 1V. When VOUT is greater than 1V, the device operates in a continuous current-limit mode that sets the output current limit to 0.9A. When VOUT is less than 1V, the device operates in short-circuit current-limit mode, sourcing 0.35ARMS current pulses to the load.
INA IN INPUT 4V TO 5.5V 0.1F 100k 100k INB
OUTA
USB PORT A 1F*
MAX1823
FAULTA FAULTB OUTB USB PORT B 1F*
Autoreset Mode
If an output fault is detected for more than the 20ms blanking time, the output latches off, the FAULT_ output goes low, and a 25mA current is forced at the output. If the voltage on the output exceeds 0.5V for 20ms, the fault resets, the 25mA current source shuts down, and the output turns on. The device monitors the output voltage so that a short-circuit condition can be detected. Active loads are not expected to have measurable currents when the supply is below 0.5V. The MAX1823
8
ONA ONB * USB APPLICATIONS MAY REQUIRE ADDITIONAL BULK CAPACITANCE.
ONA ONB
GND
Figure 1. Typical Application Circuit
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Dual USB Switch with Fault Blanking and Autoreset
Behavior During Current Limit and Fault Blanking
The MAX1823 limits switch current in three ways. When ON_ is deasserted (high for MAX1823, low for MAX1823H), the switch is off and leakage dominates the residual output current. When ON_ is asserted (low for MAX1823, high for MAX1823H), the switch supplies a continuous output current of at least 720mA. When the output current exceeds the 0.9A threshold, the MAX1823 limits the current depending on the output voltage. For VOUT_ greater than 1V (current-limit mode), the MAX1823 regulates the output current to 0.9A. For VOUT_ less than 1V (short-circuit mode), the MAX1823 pulses the switch, decreasing the current to 0.35ARMS (Table 1). Note that a thermal overload may result from either of these high-current conditions. The MAX1823 switches may enter current limit in normal operation when powering up or driving heavy capacitive loads. To differentiate these conditions from short circuits or sustained overloads that may damage the device, the MAX1823 has an independent faultblanking circuit in each switch. When a load transient causes the device to enter current limit, an internal counter starts to monitor the duration of the fault. For load faults exceeding 20ms fault-blanking time, the switch turns off, the FAULT_ signal asserts low, and the device enters autoreset mode (see Autoreset Mode). 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 FAULT_ to assert low. Fault blanking allows the MAX1823 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
INA
MAX1823/MAX1823H
FAULTA
INA ONA (ONA) CHARGE PUMP ILIM BIAS 25mA UVLO THERMAL SHUTDOWN FAULT LOGIC REF 4V TO 5.5V IN_ 0.1F OSC 25kHz TIMER 20ms OUTB 25mA GND OUTA 1F
MAX1823
(ONB) ONB INB CHARGE PUMP
ILIM
1F
INB
FAULTB
Figure 2. Functional Diagram _______________________________________________________________________________________ 9
Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
Table 1. MAX1823 Current Limiting and Fault Behavior
CONDITION * * Output Short Circuit (VOUT < 1V) * * * Output Overload Current (VOUT > 1V) MAX1823 BEHAVIOR An output short circuit ramps the current to ISHORT in 2ms to 3ms, the switch shuts off, the blanking timer turns on, FAULT_ stays high, and the output current pulses at 0.35ARMS. Removing the short circuit before the 15ms short-circuit blanking timeout period allows the next ramped current pulse to soft-start the output. The FAULT_ flag stays high. A short circuit exceeding 15ms to 20ms forces FAULT_ low at 20ms, enables autoreset mode, and sources 25mA at the output. An output voltage above 0.5V for 20ms resets the switch, turns on the output, and forces FAULT_ high. An output overload regulates the current at ILIM (0.9A), and FAULT_ stays high until the overload is removed, a thermal fault occurs, or the 20ms continuos current-limit timeout period is reached. An overcurrent condition still present at 20ms forces FAULT_ low, enables autoreset, and sources 25mA at the output. An output voltage above 0.5V for 20ms resets the switch, turns on the output, and forces FAULT_ high. A junction temperature of +160oC immediately forces FAULT_ low (the blanking timer does not apply to thermal faults) and turns off the switch. The junction cooling 15oC removes the thermal fault condition, enables autoreset mode, and sources 25mA at the output. FAULT_ remains low while a thermal fault condition is present. An output voltage above 0.5V for 20ms resets the switch, turns on the output, and forces FAULT_ high.
* * *
Thermal Fault (TJ > +160oC) *
power source. No fault is indicated if the switch is able to bring up the load within the 20ms blanking period.
Applications Information
Input Power Source
IN, INA, and INB provide the power for all control and charge-pump circuitry. All three IN_ pins must be connected together externally. The input voltage slew rate should be less than 0.2V/s to prevent erroneous FAULT_ indications. This condition should not occur under normal USB applications.
at 0.35A (RMS) until the output voltage rises above 1V, then the capacitor continues 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 does not trigger a fault output. In addition to bulk capacitance, small-value (0.1F or greater) 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 causes the output voltage at the USB port to ring during a load step. The MAX1823 is capable of driving inductive loads, but avoid exceeding the device's absolute maximum ratings. Usually the load inductance is relatively small, and the MAX1823's 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 MAX1823's output below 6V and above -0.3V.
Input Capacitor
Connect a capacitor from IN_ to ground to limit the input voltage drop during momentary output short-circuit conditions. A 0.1F ceramic capacitor is required for local decoupling; higher capacitor values will further reduce the voltage drop at the input (see Typical Operating Circuit). When driving inductive loads, a larger capacitance prevents voltage spikes from exceeding the MAX1823's absolute maximum ratings.
Output Capacitor
Place a 1F of greater capacitor at each output for noise immunity. When starting up into very large capacitive loads, the switch pulses the output current
10
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Dual USB Switch with Fault Blanking and Autoreset
Turn-On and Turn-Off Behavior
In the absence of faults, the MAX1823's internal switches turn on and 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 on the upstream power source. Under thermal fault and UVLO, the power device turns off rapidly (100ns) to protect the power device. For a 5V input and 1V output, the maximum power dissipation per switch is: P = (1.2A) ( 5V - 1V) = 4.8W Since the package power dissipation is only 444mW, the MAX1823 die temperature will exceed the thermal shutdown threshold, and the switch output shuts down until the junction temperature cools 15C. The duty cycle and period are strong functions of the ambient temperature and the PC board layout. A short circuit at the output causes the power dissipated across the switch and the junction temperature to increase. If the fault condition persists, the thermaloverload-protection circuitry activates, and the output shuts down until the junction temperature decreases by +15C (see Thermal Shutdown). Since the output short-circuit current is 25mA (typ), and with VIN_ = 5V, calculate the power dissipation for a short-circuited output as follows: P = (0.025A)(5) = 0.125W
MAX1823/MAX1823H
Layout and Thermal Dissipation
To optimize the switch response time to output shortcircuit conditions, 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 device 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. While the switches are on, power dissipation is small, and the package temperature change is minimal. Calculate the power dissipation for this condition as follows: P = (IOUT_)2 RON For the normal operating current (IOUT_ = 0.5A), and the maximum on-resistance of the switch (135m), the power dissipation is: P = (0.5A)2 x 0.135 = 34mW per switch 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)
Chip Information
TRANSISTOR COUNT: 3227 PROCESS: BiCMOS
______________________________________________________________________________________
11
Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823H
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 www.maxim-ic.com/packages.)
10LUMAX.EPS
1 1
e
10
4X S
10
INCHES MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 D2 0.114 0.120 E1 0.116 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S 0 6
MILLIMETERS MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.090 0.200 0.498 REF 0 6
H y 0.500.1 0.60.1
1
1
0.60.1
TOP VIEW
BOTTOM VIEW
D2 GAGE PLANE A2 A b D1 A1
E2 c E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
I
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.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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