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19-1903; Rev 3; 10/03
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 is removed. Each channel is guaranteed to supply 720mA and meet USB specifications. 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. Accurate internal current-limiting circuitry protects 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, undervoltagelockout (UVLO), or short-circuit fault occurs. A 20ms fault-blanking feature ignores momentary faults, such as those caused when hot swapping a capacitive load, preventing false alarms to the host system. The MAX1823A/MAX1823B also block reverse current (current from OUT_ to IN_) while in shutdown. The MAX1823 is available in a space-saving 10-pin MAX package. The MAX1823/MAX1823A are enabled with an active-low signal, and the MAX1823B/MAX1823H are enabled with an active-high signal. For a single version of this device, refer to the MAX1946 data sheet. For a triple version, refer to the MAX1940 data sheet. o Autoreset Feature Saves Power o Guaranteed 720mA Load per Channel o Built-In 20ms Fault Blanking o Compliant to USB Specification o Blocks Reverse Current in Shutdown (MAX1823A/MAX1823B) o 4V to 5.5V Input Voltage Range o Independent Shutdown Control (MAX1823/MAX1823A--Active Low) (MAX1823B/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 Recognized
Features
o Dual USB Switch in Tiny 10-Pin MAX Package
MAX1823/MAX1823A/MAX1823B/MAX1823H
Ordering Information
PART MAX1823EUB MAX1823AEUB MAX1823BEUB MAX1823HEUB TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 10 MAX 10 MAX 10 MAX 10 MAX
Applications
USB Ports and Hubs Notebook and Desktop Computers PDAs and Palmtop Computers Docking Stations
Typical Operating Circuit
INA IN OUTA USB PORT A
Pin Configuration
TOP VIEW
*(ONA) ONA 1 INA 2 IN 3 INB 4 *(ONB) ONB 5 10 FAULTA
INPUT 4V TO 5.5V
INB
MAX1823 MAX1823A
FAULTA FAULTB ONA ONB ONA ONB GND OUTB 9 8 7 6 OUTA GND OUTB FAULTB USB PORT B
MAX1823 MAX1823A MAX1823B MAX1823H
MAX
*( ) ARE FOR MAX1823B/MAX1823H.
________________________________________________________________ Maxim Integrated Products
1
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/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) MAX1823/MAX1823H, INA, IN to OUTA; INB, IN to OUTB ...................................................-0.3V to +6V MAX1823A/MAX1823B, INA, IN to OUTA; INB, IN to OUTB (when disabled, Note 3)...............-6V to +6V INA, IN to OUTA; INB, IN to OUTB (when enabled, Note 4)..............................-1.5A to +1.5ARMS 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/MAX1823A), ONA = ONB = IN (MAX1823B/MAX1823H), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Supply Voltage Range TA = +25C, each switch, MAX1823/MAX1823H TA = +25C, each switch, MAX1823A/MAX1823B Switch On-Resistance RON TA = 0C to +85C, each switch, MAX1823/MAX1823H TA = 0C to +85C, each switch, MAX1823A/MAX1823B Standby Supply Current ON_ = IN_ (MAX1823/MAX1823A), ON_ = GND (MAX1823B/MAX1823H) IOUTA = IOUTB = 0A, one channel on IOUTA = IOUTB = 0A, both channels on ON_ = IN_ (MAX1823/MAX1823A), ON_ = GND (MAX1823B/MAX1823H), VOUTA = VOUTB = 0V, TA = +25oC OUT_ Off-Leakage Current ON_ = IN_ (MAX1823/MAX1823A), ON_ = GND (MAX1823B/MAX1823H), VOUTA = VOUTB = 0V, TA = 0oC to +85oC Undervoltage-Lockout Threshold Continuous Load Current Continuous Current Limit Short-Circuit Current Limit ILIM ISHORT VIN - VOUT_ = 0.5V VOUT_ = 0V (IOUT pulsing) VOUT_ = 0V (IOUT pulsing) VUVLO Rising edge, 3% hysteresis 3.0 720 0.72 0.8 0.90 1.2 0.35 1.20 1.6 0.02 3.4 10.00 3.8 V mA A APEAK ARMS 3 SYMBOL CONDITIONS MIN 4.0 75 90 TYP MAX 5.5 105 120 m 135 165 10 A UNITS V
Quiescent Supply Current
40 50 0.02
80 100 1.00
A
A
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/MAX1823A), ONA = ONB = IN (MAX1823B/MAX1823H), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Short-Circuit Detect Threshold Continuous Current-Limit Blanking Timeout Period Short-Circuit Blanking Timeout Period Turn-On Delay Output Rise Time tON tRISE SYMBOL (Note 1) From continuous current-limit condition to FAULT_ assertion From short-circuit current-limit condition to FAULT_ assertion ROUT_ = 10k, does not include rise time MAX1823/MAX1823H MAX1823A/MAX1823B 10 7.5 0.5 0.3 CONDITIONS MIN TYP 1 20 18 1.2 0.8 2.5 0.8 3.0 ms ROUT_ = 10, does not include fall time (from ON_ (MAX1823A) or ON_ (MAX1823B) deasserted to VOUT = 90% of VIN_) ROUT_ = 10, from 90% to 10% of VOUT_ (MAX1823/MAX1823H) Output Fall Time tFALL ROUT_ = 10, from 90% to 10% of VOUT_ (MAX1823A/MAX1823B) 15oC hysteresis VIN_ = 4V to 5.5V VIN_ = 4V to 5.5V ON_ = GND or IN_ (MAX1823/MAX1823A), ON_ = GND or IN_ (MAX1823B/MAX1823H) ISINK = 1mA, VIN_ = 4V VIN_ = V FAULT_ = 5.5V In latched-off state, VOUT_ = 0V In latched-off state, rising In latched-off state, VOUT_ > 0.5V 10 0.4 10 30 0.5 20 -1 2 0.8 +1 0.4 1 45 0.6 35 0.1 3.0 35 35.0 4.0 ms 3.0 ms MAX UNITS V ms ms
MAX1823/MAX1823A/MAX1823B/MAX1823H
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_)
Turn-Off Delay from ON
tOFF
2.5 ms 2.8 +160
o
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
C
V V A V A mA V ms
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823B/MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823/MAX1823A), TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER Supply Voltage Range Switch On-Resistance Standby Supply Current RON Each switch, MAX1823/MAX1823H Each switch, MAX1823A/MAX1823B ON_ = IN_ (MAX1823/MAX1823A), ON_ = GND (MAX1823B/MAX1823H) IOUTA = IOUTB = 0A, one channel on Quiescent Supply Current IOUTA = IOUTB = 0A, both channels on ON_ = IN_ (MAX1823/MAX1823A), ON_ = GND (MAX1823B/MAX1823H), VOUTA = VOUTB = 0V VUVLO ILIM ISHORT Rising edge, 3% hysteresis VIN_ - VOUT_ = 0.5V VOUT_ = 0V (IOUT pulsing) From continuous current-limit condition to FAULT_ assertion From short-circuit current-limit condition to FAULT_ assertion tON ROUT_ = 10k, does not include rise time MAX1823/MAX1823H MAX1823A/MAX1823B 3.0 720 0.72 0.8 10 7.5 0.5 0.3 1.20 1.6 35 35.0 4.0 ms 3.0 100 SYMBOL CONDITIONS MIN 4.0 TYP MAX 5.5 135 165 10 UNITS V m A
80 A
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
Turn-Off Delay from ON
tOFF
ROUT_ = 10, does not include fall time (from ON_ (MAX1823/MAX1823A) or ON_ (MAX1823B/MAX1823H) deasserted to VOUT_ = 90% VIN_)
3
ms
4
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Dual USB Switch with Fault Blanking and Autoreset
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823B/MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823/MAX1823A), TA = -40C to +85C, unless otherwise noted.) (Note 2)
PARAMETER 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 VIN_= 4V to 5.5V VIN_= 4V to 5.5V V ON_ = 0V or VIN_ ISINK = 1mA, VIN_ = 4V VIN_ = V FAULT_ = 5.5V In latched-off state, VOUT_ = 0V In latched-off state, rising In latched-off state, VOUT_ > 0.5V 10 0.4 10 -1 MIN 2 0.8 +1 0.4 1 50 0.6 35 TYP MAX UNITS V V A V A mA V ms
MAX1823/MAX1823A/MAX1823B/MAX1823H
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. Note 3: Reverse current (current from OUT_ to IN_) is blocked when disabled. Note 4: Forward current (current from IN_ to OUT_) is internally limited. Reverse current, from OUT_ to IN_, is not limited when the device is enabled and must be kept below 1.5ARMS to prevent permanent device damage. When the MAX1823A/MAX1823B are disabled, the switch turns off and reverse current is internally blocked.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823/MAX1823A), ON_ = IN_ (MAX1823B/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/MAX1823A) ON_ = GND (MAX1823B/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)
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823/MAX1823A), ON_ = IN_ (MAX1823B/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
1.50
940 CONTINUOUS CURRENT LIMIT (mA)
SWITCH OFF-LEAKAGE (nA)
100
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 (tON + tRISE)
MAX1823 toc07
TURN-OFF TIME vs. TEMPERATURE (tOFF + tFALL)
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
MAX1823 toc10
AUTORESET CURRENT vs. TEMPERATURE (MAX1823/MAX1823H)
MAX1823 toc11
AUTORESET CURRENT vs. TEMPERATURE (MAX1823A/MAX1823B)
MAX1823 toc12
0.250 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 VIN_ = 5.5V VIN_ = 5V
40 VIN_ = 5.5V
36
AUTORESET CURRENT (mA)
AUTORESET CURRENT (mA)
35
34
VIN_ = 5.5V
30
VIN_ = 5V 32
25
30 VIN_ = 4.5V 28
20 VIN_ = 4.5V 15 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C) VIN_ = 5V
-40
-15
10
35
60
85
TEMPERATURE (C)
6
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823/MAX1823A), ON_ = IN_ (MAX1823B/MAX1823H), TA = +25C, unless otherwise noted.)
AUTORESET CURRENT vs. INPUT VOLTAGE (MAX1823/MAX1823H)
MAX1823 toc13
AUTORESET CURRENT vs. INPUT VOLTAGE (MAX1823A/MAX1823B)
MAX1823 toc14
OVERLOAD RESPONSE INTO 2.5 (MAX1823/MAX1823H)
MAX1823 toc15
50 TA = -40C AUTORESET CURRENT (mA) 40 TA = +25C 30
39 37 AUTORESET CURRENT (mA) 35
A
5V
B 33 TA = +25C 31 29 27 25 TA = -40C D C TA = +85C
0
20 TA = +85C 10
0
0 10ms/div C: VFAULTA, 5V/div D: IOUTA, 1A/div
0 3.6 4.4 5.2 6.0 INPUT VOLTAGE (V)
3.6
4.4
5.2
6.0 A: VIN_, 5V/div B: VOUTA, 5V/div
INPUT VOLTAGE (V)
OVERLOAD RESPONSE INTO 2.5 (MAX1823A/MAX1823B ONLY)
MAX1823 toc16
OVERLOAD RESPONSE INTO 2.5 (EXPANDED TIME SCALE)
MAX1823 toc17
SHORT-CIRCUIT RESPONSE INTO 0 (MAX1823/MAX1823H)
MAX1823 toc18
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: VIN_, 5V/div B: VOUTA, 5V/div
A: VIN_, 5V/div B: VOUTA, 5V/div
A: VIN_, 5V/div B: VOUTA, 5V/div
SHORT-CIRCUIT RESPONSE INTO 0 (MAX1823A/MAX1823B)
MAX1823 toc19
SHORT-CIRCUIT RESPONSE INTO 0 (EXPANDED TIME SCALE)
MAX1823 toc20
SWITCH TURN-ON TIME (MAX1823/MAX1823A)
MAX1823 toc21
A B
5V
A
5V
A 0
0
B C
0 5V
C 0
B D 0 10ms/div C: VFAULTA, 5V/div D: IOUTA, 2A/div D 0 0 1ms/div
A: VIN_, 5V/div B: VOUTA, 5V/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
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_ = GND (MAX1823/MAX1823A), ON_ = IN_ (MAX1823B/MAX1823H), TA = +25C, unless otherwise noted.)
SWITCH TURN-OFF TIME (tOFF + tFALL)
STARTUP TIME (TYPICAL USB APPLICATION)
MAX1823 toc23
MAX1823 toc22
A A 0 B
0 5V
C 0 B D 0 1ms/div A: VONA, 5V/div B: VOUTA, 2V/div A: VONA, 5V/div B: VFAULTA, 5V/div 500s/div C: VOUTA, 2V/div D : IOUTA, 0.5A/div 0
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/MAX1823A, and a logic high turns switch A on for the MAX1823B/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/MAX1823A, and a logic high turns switch B on for the MAX1823B/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 the MAX1823B/MAX1823H only.
8
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Dual USB Switch with Fault Blanking and Autoreset
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.
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.
MAX1823/MAX1823A/MAX1823B/MAX1823H
Reverse Current Blocking
The USB specification does not allow an output device to source current back into the USB port. However, the MAX1823A/MAX1823B are designed to safely power noncompliant devices. When disabled, each output is switched to a high-impedance state, blocking reverse current flow from the output back to the input. However, during normal operation with the device enabled, the MAX1823A/MAX1823B are bidirectional switches.
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.
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 brownout 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 VOUT 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 INB 0.1F 100k 100k
OUTA
USB PORT A 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/MAX1823A can also be reset from fault manually by toggling ON_ (ON_ for the MAX1823B/MAX1823H) for that channel.
MAX1823
FAULTA FAULTB OUTB USB PORT B 1F*
ONA ONB * USB APPLICATIONS MAY REQUIRE ADDITIONAL BULK CAPACITANCE.
ONA ONB
GND
Figure 1. Typical Application Circuit 9
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
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. 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 the Autoreset Mode section). 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.
INA
Behavior During Current Limit and Fault Blanking
The MAX1823 limits switch current in three ways. When ON_ is deasserted (high for MAX1823/MAX1823A, low for MAX1823B/MAX1823H), the switch is off and leakage dominates the residual output current. When ON_ is asserted (low for MAX1823/MAX1823A, high for MAX1823B/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 V OUT_ greater than 1V (current-limit mode), the MAX1823 regulates the output current to 0.9A. For
FAULTA
INA ONA *(ONA) CHARGE PUMP ILIM OUTA UVLO THERMAL SHUTDOWN 25mA 1F
BIAS
REF 4V TO 5.5V IN_ 0.1F OSC 25kHz TIMER 20ms
FAULT LOGIC
GND
25mA OUTB
MAX1823/MAX1823A MAX1823B/MAX1823H
*(ONB) ONB INB CHARGE PUMP
ILIM
1F
INB
*( ) ARE FOR THE MAX1823B/MAX1823H.
FAULTB
Figure 2. Functional Diagram 10 ______________________________________________________________________________________
Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
Table 1. MAX1823 Current Limiting and Fault Behavior
CONDITION * * Output short circuit (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 continuous 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 +160C immediately forces FAULT_ low (the blanking timer does not apply to thermal faults) and turns off the switch. The junction cooling 15C 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.
* Output overload current (VOUT > 1V)
* *
* Thermal fault (TJ > +160C)
*
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 power source. No fault is indicated if the switch is able to bring up the load within the 20ms blanking period.
Output Capacitor
Place a 1F or greater capacitor at each output for noise immunity. When starting up into very large capacitive loads, the switch pulses the output current at 0.35ARMS 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).
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.
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 avoids 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.
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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 further reduce the voltage drop at the input (see the Typical Application Circuit (Figure 1)). When driving inductive loads, a larger capacitance prevents voltage spikes from exceeding the MAX1823's absolute maximum ratings.
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Dual USB Switch with Fault Blanking and Autoreset MAX1823/MAX1823A/MAX1823B/MAX1823H
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 provided in the Electrical Characteristics table. The slow chargepump 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 exceeds the thermalshutdown threshold, and the switch output shuts down until the junction temperature cools by 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 the Thermal Shutdown section). 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
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
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Dual USB Switch with Fault Blanking and Autoreset
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
MAX1823/MAX1823A/MAX1823B/MAX1823H
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 A1 D1
E2
c
E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
1 1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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