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 specifica-
tions. The device’s low quiescent supply current (50µA)
and standby current (3µA) conserve battery power in
portable applications.
The MAX1823 has multiple safety features to ensure that
the USB port is protected. Built-in thermal-overload pro-
tection limits power dissipation and junction temperature.
The device also has accurate internal current-limiting cir-
cuitry to protect the input supply against both overload
and short-circuit conditions. Independent fault signals
(FAULTA and FAULTB) notify the microprocessor (µP)
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
µMAX. 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.
Applications
USB Ports and Hubs
Notebook and Desktop Computers
PDAs and Palmtop Computers
Docking Stations
Features
♦Dual USB Switch in Tiny 10-Pin µMAX Package
♦Autoreset Feature Saves Power
♦Guaranteed 720mA Load per Channel
♦Built-In 20ms Fault Blanking
♦Compliant to USB Specification
♦4V to 5.5V Input Voltage Range
♦Independent Shutdown Control
(MAX1823—Active Low)
(MAX1823H—Active High)
♦Independent FAULT Indicator Outputs
♦Thermal-Overload Protection
♦50µA Quiescent Current (Both Switches On)
♦3µA Standby Current
♦UL Listing Pending
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
Typical Operating Circuit
19-1903; Rev 2; 10/02
PART TEMP RANGE PIN-PACKAGE
MAX1823EUB -40°C to +85°C 10 µMAX
MAX1823HEUB
-40°C to +85°C 10 µMAX
Pin Configuration
ONBONB
ONAONA
GND
MAX1823
FAULTB
FAULTA
IN
INA
INB
USB
PORT A
OUTA
USB
PORT B
OUTB
INPUT
4V TO 5.5V
1
2
3
4
5
10
9
8
7
6
OUTA
GND
OUTBINB
IN
INA
MAX1823
µMAX
TOP VIEW
ONA
ONB FAULTB
FAULTA
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
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= +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
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
UNITS
Supply Voltage Range 4.0 5.5 V
TA = +25oC, each switch 75
105
Switch On-Resistance RON TA = 0oC to +85oC, each switch
135
mΩ
Standby Supply Current
ON_ = IN _ ( MAX 1823), ON _ = GN D ( MAX 1823H)
310µA
ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H) IOUTA = IOUTB = 0 40 80
Quiescent Supply Current
IOUTA = IOUTB = 0 50
100
µA
ON_ = IN _ ( MAX 1823), ON _ = GND (M AX1823H)
VOUTA = VOUTB = 0, TA = +25oC
0.02 1.00
OUT_ Off-Leakage Current ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H)
VOUTA = VOUTB = 0, TA = 0oC to +85oC
0.02 10.00
µA
Undervoltage Lockout Threshold
VUVLO Rising edge, 3% hysteresis 3.0 3.4 3.8 V
Continuous Load Current
720
mA
Continuous Current Limit ILIM VIN - VOUT_ = 0.5V
0.72 0.90 1.20
A
VOUT_ = 0 (IOUT pulsing) 0.8 1.2 1.6
A(peak)
Short-Circuit Current Limit ISHORT VOUT_ = 0 (IOUT pulsing)
0.35
ARMS
Short-Circuit Detect Threshold (Note 1) 1 V
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, does not include rise time
(from ON_ (MAX1823) or ON_ (MAX1823H)
asserted to VOUT = 10% VIN_)
0.5 1.2 4.0 ms
Output Rise Time ROUT_ = 10Ω, from 10% to 90% of VOUT_ 2.5 ms
Turn-Off Delay from ON
ROUT_ = 10Ω, does not include fall time
(from ON_ (MAX1823) or ON_ (MAX1823H)
deasserted to VOUT = 90% of VIN_)
0.8 3.0 ms
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ONA = ONB = GND (MAX1823), ONA = ONB = IN (MAX1823H), TA = 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.)
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823), TA = -40°C to +85°C, unless oth-
erwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
UNITS
Supply Voltage Range 4.0 5.5 V
Switch On-Resistance RON Each switch
135
mΩ
Standby Supply Current ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H) 10 µA
ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H) IOUTA = IOUTB = 0 80
Quiescent Supply Current ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H) IOUTA = IOUTB = 0
100
µA
OUT_ Off-Leakage Current
ON_ = IN_ (MAX1823), ON_ = GND
(MAX1823H)
VOUTA = VOUTB = 0
10 µA
Undervoltage Lockout Threshold
VUVLO Rising edge, 3% hysteresis 3.0 3.8 V
Continuous Load Current
720
mA
Continuous Current Limit ILIM VIN_ - VOUT_ = 0.5V
0.72 1.20
A
Current Limit into Short Circuit ISHORT VOUT_ = 0 (IOUT pulsing) 0.8 1.6
APEAK
Continuous Current-Limit
Blanking Timeout Period
From continuous current-limit condition to
FAULT_ assertion 10 35 ms
Short-Circuit Blanking Timeout
Period
From short-circuit current-limit condition to
FAULT_ assertion 7.5
35.0
ms
Turn-On Delay
ROUT_ = 10Ω, does not include rise time
(from ON_ (MAX1823) or ON_ (MAX1823H)
asserted to VOUT_ = 10% VIN_)
0.5 4.0 ms
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Output Fall Time ROUT_ = 10Ω, from 10% to 90% of VOUT_ 2.5 ms
Thermal Shutdown Threshold 15oC hysteresis 160 oC
Logic Input High Voltage VIN_ = 4V to 5.5V 2 V
Logic Input Low Voltage VIN_ = 4V to 5.5V 0.8 V
Logic Input Current ON_ = GND or IN_ (MAX1823), ON_ = GND
or IN_ (MAX1823H) -1 1 µA
FAULT_ Output Low Voltage ISINK = 1mA, VIN_ = 4V 0.4 V
FAULT_ Output High Leakage
Current VIN_ = VFAULT_ = 5.5V 1 µA
Autoreset OUT_ Current In latched-off state, VOUT_ = 0 10 25 45 mA
Autoreset Threshold In latched-off state, rising 0.4 0.5 0.6 V
Autoreset Blanking Time In latched-off state, VOUT_ > 0.5V 10 20 35 ms
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ONA = ONB = GND (MAX1823), ONA = ONB = IN (MAX1823H), TA = 0°C to +85°C, unless
otherwise noted. Typical values are at TA= +25°C.)
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = VIN_ = VON_ = 5V (MAX1823H); VIN = VIN_ = 5V, ON_ = GND (MAX1823) TA = -40°C to +85°C, unless oth-
erwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
UNITS
Turn-Off Delay from ON
ROUT_ = 10Ω, does not include fall time
(from ON_ (MAX1823) or ON_ (MAX1823H)
deasserted to VOUT_ = 90% VIN_)
3ms
Logic Input High Voltage VIN_= 4V to 5.5V 2 V
Logic Input Low Voltage VIN_= 4V to 5.5V 0.8 V
Logic Input Current VON_ = 0 or VIN_ -1 +1 µA
FAULT_ Output Low Voltage ISINK = 1mA, VIN_ = 4V 0.4 V
FAULT_ Output High Leakage
Current VIN_ = VFAULT_ = 5.5V 1 µA
Autoreset OUT_Current In latched-off state, VOUT_ = 0 10 50 mA
Autoreset Threshold In latched-off state, rising 0.4
0.6
V
Autoreset Blanking Time In latched-off state, VOUT_ > 0.5V 10 35 ms
Note 1: The output voltage at which the device transitions from short-circuit current limit to continuous current limit.
Note 2: Specifications to -40°C 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= +25°C, unless otherwise noted.)
0
18
12
6
24
30
36
42
48
54
60
021 3456
QUIESCENT CURRENT
vs. INPUT VOLTAGE
MAX1823 toc01
INPUT VOLTAGE (V)
QUIESCENT CURRENT (µA)
45
47
51
49
53
55
-40 10-15 35 60 85
QUIESCENT CURRENT
vs. TEMPERATURE
MAX1823 toc02
TEMPERATURE (°C)
QUIESCENT CURRENT (µA)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
2.5
2.7
3.1
2.9
3.3
3.5
-40 10-15 35 60 85
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX1823 toc03
TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT (µA)
ON_ = IN_ (MAX1823)
ON_ = GND (MAX1823H)
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
_______________________________________________________________________________________ 5
940
930
920
910
900
-40 10-15 35 60 85
MAX1823 toc06
TEMPERATURE (°C)
CONTINUOUS CURRENT LIMIT (mA)
CONTINUOUS CURRENT-LIMIT
THRESHOLD vs. TEMPERATURE
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
0.01
0.1
10
1
100
1000
-40 10-15 35 60 85
SWITCH OFF-LEAKAGE
vs. TEMPERATURE
MAX1823 toc04
TEMPERATURE (°C)
SWITCH OFF-LEAKAGE (nA)
ON_ = IN_ (MAX1823)
ON_ = GND (MAX1823H)
1.50
1.25
1.00
0.75
0.50
-40 10-15 35 60 85
NORMALIZED RON vs. TEMPERATURE
MAX 1823 toc05
TEMPERATURE (°C)
NORMALIZED RON
3.0
3.2
3.6
3.4
3.8
4.0
-40 10-15 35 60 85
TURN-ON TIME
vs. TEMPERATURE
MAX1823 toc07
TEMPERATURE (°C)
TURN-ON TIME (ms)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
2.5
2.7
3.1
2.9
3.3
3.5
-40 10-15 35 60 85
TURN-OFF TIME
vs. TEMPERATURE
MAX1823 toc08
TEMPERATURE (°C)
TURN-OFF TIME (ms)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
21.0
21.2
21.6
21.4
21.8
22.0
-40 10-15 35 60 85
FAULT-BLANKING TIME
vs. TEMPERATURE
MAX1823 toc09
TEMPERATURE (°C)
FAULT-BLANKING TIME (ms)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
0.100
0.150
0.125
0.200
0.175
0.225
0.250
-40 10-15 35 60 85
FAULT_ OUTPUT LOW VOLTAGE
vs. TEMPERATURE
MAX1823 toc10
TEMPERATURE (°C)
FAULT_ OUTPUT LOW VOLTAGE (V)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
IFAULT_ = 1mA
15
20
30
25
35
40
-40 10-15 35 60 85
AUTORESET CURRENT
vs. TEMPERATURE
MAX1823 toc11
TEMPERATURE (°C)
AUTORESET CURRENT (mA)
VIN_
=
5.5V
VIN_
=
4.5V
VIN_
=
5V
0
10
30
20
40
50
MAX1823 toc12
INPUT VOLTAGE (V)
AUTORESET CURRENT (mA)
3.6 5.24.4 6.0
AUTORESET CURRENT
vs. INPUT VOLTAGE
TA = +25°C
TA = -40°C
TA = +85°C
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_=GND (MAX1823), ON_ = IN_ (MAX1823H), TA= +25°C, unless otherwise noted.)
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
6 _______________________________________________________________________________________
10ms/div
OVERLOAD RESPONSE INTO 2.5Ω
A: VIN_, 5V/div
B: VOUTA, 5V/div
C: VFAULTA, 5V/div
D: IOUTA, 1A/div
A
B
D
C
MAX1823 toc13
5V
0
0
0
500µs/div
OVERLOAD RESPONSE INTO 2.5Ω
(EXPANDED TIME SCALE)
A: VIN_, 5V/div
B: VOUTA, 5V/div
A
B
D
C
MAX1823 toc14
5V
0
0
0
C: VFAULTA, 5V/div
D: IOUTA, 1A/div
10ms/div
SHORT-CIRCUIT RESPONSE INTO 0Ω
A
B
D
C
MAX1823 toc15
5V
0
0
0
C: VFAULTA, 5V/div
D: IOUTA, 1A/div
A: VIN_, 5V/div
B: VOUTA, 5V/div
500µs/div
SHORT-CIRCUIT RESPONSE INTO 0Ω
(EXPANDED TIME SCALE)
A: VIN_, 5V/div
B: VOUTA, 5V/div
A
B
D
C
MAX1823 toc16
5V
0
5V
0
C: VFAULTA, 5V/div
D: IOUTA, 2A/div
1ms/div
SWITCH TURN-ON TIME
(MAX1823)
A: VONA, 5V/div
B: VOUTA, 2V/div
A
B
MAX1823 toc17
0
0
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_=GND (MAX1823), ON_ = IN_ (MAX1823H), TA= +25°C, unless otherwise noted.)
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
_______________________________________________________________________________________ 7
Pin Description
PIN NAME FUNCTION
1ONA
*(ONA)
C ontr ol Inp ut for S w i tch A. C an b e d r i ven hi g her than IN_ w i thout d am ag e. A l og i c l ow tur ns sw i tch A on for
the M AX 1823, and a l og i c hi g h tur ns sw i tch A on for the M AX 1823H .
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.
5ONB
*(ONB)
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.
6FAULTB 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.
7 OUTB Power Output for Switch B. Connect a 1µF capacitor from OUTB to ground. Load condition may
require additional bulk capacitance.
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.
10 FAULTA 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.
1ms/div
SWITCH TURN-OFF TIME
A: VONA, 5V/div
B: VOUTA, 2V/div
A
B
MAX1823 toc18
0
0
500µs/div
STARTUP TIME
(TYPICAL USB APPLICATION)
A: VONA, 5V/div
B: VFAULTA, 5V/div
A
B
MAX1823 toc19
0
5V
C
D
0
0
C: VOUTA, 2V/div
D : IOUTA, 0.5A/div
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VINA = VINB = 5V, ON_=GND (MAX1823), ON_ = IN_ (MAX1823H), TA= +25°C, unless otherwise noted.)
*() are for MAX1823H only
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
8 _______________________________________________________________________________________
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 cur-
rent. 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 auto-
matically 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 µMAX
package. An internal micropower charge pump gener-
ates 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.
Undervoltage Lockout and
Input Voltage Requirements
The MAX1823 includes a UVLO circuit to prevent erro-
neous 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 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 cur-
rent-limit mode, sourcing 0.35ARMS current pulses to
the load.
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 detect-
ed. Active loads are not expected to have measurable
currents when the supply is below 0.5V. The MAX1823
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 +160°C, the
switch turns off, and the FAULT_ output goes low
immediately; fault blanking does not occur during ther-
mal limit. When the junction cools by 15°C, the switch
turns on again. If the fault overload condition continues,
the switch cycles on and off, resulting in a pulsed out-
put, saving battery power.
Fault Indicators
The MAX1823 provides an open-drain fault output
(FAULT_) for each switch. For most applications, con-
nect FAULT_ to IN_ through a 100kΩpullup 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
+160°C 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/µs may cause erroneous FAULT_
indications.
ONBONB
ONAONA
GND
MAX1823
FAULTB
FAULTA
IN
INA
INB
USB
PORT A
OUTA
USB
PORT B
OUTB
INPUT
4V TO 5.5V
0.1µF
100kΩ
100kΩ
1µF*
* USB APPLICATIONS MAY REQUIRE
ADDITIONAL BULK CAPACITANCE.
1µF*
Figure 1. Typical Application Circuit
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
_______________________________________________________________________________________ 9
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 nor-
mal 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 fault-
blanking 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 suc-
cessfully powered even while protecting the upstream
ONA
MAX1823
CHARGE
PUMP
ONB
CHARGE
PUMP
(ONA)
(ONB)
OSC
25kHz
BIAS
UVLO
REF
GND
0.1µF
4V TO 5.5V
IN_
TIMER
20ms
THERMAL
SHUTDOWN
FAULT
LOGIC
ILIM
25mA
25mA
1µF
OUTA
FAULTB
FAULTA
ILIM 1µF
OUTB
INA
INA
INB
INB
Figure 2. Functional Diagram
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
10 ______________________________________________________________________________________
Table 1. MAX1823 Current Limiting and Fault Behavior
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 con-
nected together externally. The input voltage slew rate
should be less than 0.2V/µs to prevent erroneous
FAULT_ indications. This condition should not occur
under normal USB applications.
Input Capacitor
Connect a capacitor from IN_ to ground to limit the
input voltage drop during momentary output short-cir-
cuit conditions. A 0.1µF 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 1µF of greater capacitor at each output for
noise immunity. When starting up into very large
capacitive loads, the switch pulses the output current
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 capac-
itor must charge up within the fault-blanking delay peri-
od. Typically, starting up into a 330µF or smaller
capacitor does not trigger a fault output. In addition to
bulk capacitance, small-value (0.1µF 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 induc-
tance 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 regula-
tor as well as local bypass capacitors, limiting over-
shoot. If severe ringing occurs due to large load
inductance, clamp the MAX1823’s output below 6V and
above -0.3V.
CONDITION MAX1823 BEHAVIOR
Output Short Circuit
(VOUT < 1V)
•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.
Output Overload Current
(VOUT > 1V)
•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.
Thermal Fault
(TJ > +160oC)
•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.
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
______________________________________________________________________________________ 11
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.
Layout and Thermal Dissipation
To optimize the switch response time to output short-
circuit conditions, keep all traces as short as possible
to reduce the effect of undesirable parasitic induc-
tance. 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 fol-
lows:
P = (IOUT_)2RON
For the normal operating current (IOUT_ = 0.5A), and
the maximum on-resistance of the switch (135mΩ), the
power dissipation is:
P = (0.5A)2x 0.135Ω= 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)
For a 5V input and 1V output, the maximum power dis-
sipation 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 15°C. 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 thermal-
overload-protection circuitry activates, and the output
shuts down until the junction temperature decreases by
+15°C (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
Chip Information
TRANSISTOR COUNT: 3227
PROCESS: BiCMOS
MAX1823/MAX1823H
Dual USB Switch with Fault
Blanking and Autoreset
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
© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
10LUMAX.EPS
PACKAGE OUTLINE, 10L uMAX/uSOP
1
1
21-0061 I
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
1
0.498 REF
0.0196 REF
S
6∞
SIDE VIEW
α
BOTTOM VIEW
0∞0∞6∞
0.037 REF
0.0078
MAX
0.006
0.043
0.118
0.120
0.199
0.0275
0.118
0.0106
0.120
0.0197 BSC
INCHES
1
10
L1
0.0035
0.007
e
c
b
0.187
0.0157
0.114
H
L
E2
DIM
0.116
0.114
0.116
0.002
D2
E1
A1
D1
MIN
-A
0.940 REF
0.500 BSC
0.090
0.177
4.75
2.89
0.40
0.200
0.270
5.05
0.70
3.00
MILLIMETERS
0.05
2.89
2.95
2.95
-
MIN
3.00
3.05
0.15
3.05
MAX
1.10
10
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
H
4X S
e
D2
D1
b
A2 A
E2
E1 L
L1
c
α
GAGE PLANE
A2 0.030 0.037 0.75 0.95
A1
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.)