MAX1823EUBT [MAXIM]
1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO10, MICRO MAX PACKAGE-10;
| 型号： | MAX1823EUBT |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO10, MICRO MAX PACKAGE-10 信息通信管理 光电二极管 |
| 文件： | 总11页 (文件大小：324K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1903; Rev 0; 2/01
Dual USB Switch with Fault
Blanking and Autoreset
General Description
Features
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 chan-
nel is guaranteed to supply 500mA and meet USB speci-
fications. 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.
• Dual USB Switch in Tiny 10-Pin µMAX Package
• Autoreset Feature Saves Power
• Guaranteed 500mA Load per Channel
• Built-In 20ms Fault Blanking
• Compliant to USB Specification
• 4.0V to 5.5V Input Voltage Range
• Independent Shutdown Control
• Independent FAULT Indicator Outputs
• Thermal Overload Protection
• 0.50µA Quiescent Current (Both Switches On)
• 3µA Standby Current
• UL Listing Pending
The MAX1823 is available in a space-saving 10-pin
µMAX. 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.
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX1823EUB
-40°C to +85°C
10 µMAX
Applications
USB Ports
USB Hubs
Notebook Computers
Desktop Computers
PDAs and Palmtop Computers
Docking Stations
Pin Configuration
Typical Operating Circuit
USB
PORT A
INA
IN
OUTA
TOP VIEW
INPUT
4.0V TO 5.5V
INB
ONA
INA
IN
1
2
3
4
5
10 FAULTA
MAX1823
9
8
7
6
OUTA
GND
MAX1823
USB
PORT B
FAULTA
FAULTB
OUTB
INB
ONB
OUTB
FAULTB
ONA
ONB
ONA
ONB
GND
µMAX
________________________________________________________________ Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Dual USB Switch with Fault
Blanking and Autoreset
ABSOLUTE MAXIMUM RATINGS
IN, INA, INB, ONA, ONB, OUTA, OUTB to GND ........-0.3V to 6V
FAULTA, FAULTB to GND..........................-0.3V to (V + 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 (T = +70°C)
A
10-Pin µMAX (derate 5.6mW/°C above +70°C)...............444mW
IN_
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V = V
= V
= 5V, V
= V
= GND, T = 0°C to +85°C, unless otherwise noted. Typical values are at
ONB A
IN
INA
INB
ONA
T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
5.5
UNITS
Supply Voltage Range
Switch On-Resistance
Standby Supply Current
4.0
V
T
T
= +25°C, each switch
75
105
135
10
A
A
R
mΩ
µA
ON
= +0°C to +85°C, each switch
V
V
V
= V
= V
= V
= V _
IN
3
ONA
ONA
ONA
ONB
ONB
ONB
= V _, I
= I
= 0
40
50
80
IN OUTA
OUTB
Quiescent Supply Current
µA
= 0, I
= I
OUTB
= 0
100
OUTA
V
= V
= +25°C
= V _, V
= V
= V
= 0,
= 0,
ONA
ONB
IN
OUTA
OUTB
0.02
1
T
A
OUT_ Off-Leakage Current
µA
V
= V
= V _, V
ONB IN OUTA
ONA
OUTB
0.02
3.4
10
T
= 0°C to +85°C
A
Undervoltage Lockout Threshold
Continuous Load Current
Continuous Current Limit
V
Rising edge, 3% hysteresis
3.0
500
0.6
0.8
3.8
V
mA
A
UVLO
I
V
V
V
_ - V _ = 0.5V
OUT
0.9
1.2
0.35
1
1.2
1.6
LIM
IN
_ = 0 (I
_ = 0 (I
_ pulsing)
_ pulsing)
A
PEAK
OUT
OUT
OUT
OUT
Short-Circuit Current Limit
I
SHORT
A
RMS
V
Short-Circuit Detect Threshold
(Note 1)
Continuous Current-Limit Blanking
Timeout Period
From continuous current-limit condition to
FAULT_ assertion
10
7.5
0.5
20
18
35
35
4.0
ms
ms
Short-Circuit Blanking Timeout
Period
From short-circuit current-limit condition to
FAULT_ assertion
R
_ = 10Ω, does not include rise time
OUT
Turn-On Delay
1.2
2.5
0.8
ms
ms
ms
(from ON_ to 10% of V
_)
OUT
Output Rise Time
Turn-Off Delay from ON
R
OUT
_ = 10Ω, from 10% to 90% of V
_
OUT
R
_ = 10Ω, does not include fall time (from
_)
OUT
3
ON_ to 90% of V
OUT
Output Fall Time
R
_ = 10Ω, from 10% to 90% of V
_
2.5
ms
°C
V
OUT
OUT
Thermal Shutdown
15°C hysteresis
160
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
V
V
V
_ = 4V to 5.5V
_ = 4V to 5.5V
2
IN
0.8
1
V
IN
= 0 or V
_
IN
-1
µA
ON_
2
_______________________________________________________________________________________
Dual USB Switch with Fault
Blanking and Autoreset
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = V
IN
= V
= 5V, V
= V
= GND, T = 0°C to +85°C, unless otherwise noted. Typical values are at
ONB A
INA
INB
ONA
PARAMETER
SYMBOL
CONDITIONS
= 1mA, V _ = 4V
MIN
TYP
MAX
UNITS
FAULT_ Output Low Voltage
I
0.4
V
SINK
IN
FAULT_ Output High Leakage
Current
V
_ = V
= 5.5V
FAULT_
1
µA
IN
Autoreset OUT_ Current
Autoreset Threshold
In latched-off state, V
_ = 0
10
0.4
10
25
0.5
20
45
0.6
35
mA
V
OUT
In latched-off state, rising
In latched-off state, V
Autoreset Blanking Time
_ > 0.5V
ms
OUT
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V = V
IN
= V
= 5V, V
= V
= GND, T = -40°C to +85°C, unless otherwise noted.) (Note 2)
ONB A
INA
INB
ONA
PARAMETER
Supply Voltage Range
Switch On-Resistance
Standby Supply Current
SYMBOL
CONDITIONS
MIN
TYP
MAX
5.5
135
10
UNITS
V
4.0
R
Each switch
mΩ
µA
ON
V
V
V
= V
= V
= V
= V _
IN
ONA
ONA
ONA
ONB
ONB
ONB
= V _, I
= I
= 0
80
IN OUTA
OUTB
Quiescent Supply Current
µA
µA
= 0, I
= I
OUTB
= 0
100
OUTA
OUT_ Off-Leakage Current
V
= V
= V _, V
= V = 0
OUTB
10
ONA
ONB
IN
OUTA
Undervoltage Lockout Threshold
Continuous Load Current
V
Rising edge, 3% hysteresis
3.0
500
0.6
0.8
3.8
V
mA
A
UVLO
Continuous Current Limit
I
V
V
_ - V _ = 0.5V
OUT
1.2
1.6
LIM
IN
Current Limit into Short Circuit
I
_ = 0 (I
pulsing)
A
PEAK
SHORT
OUT
OUT
Continuous Current-Limit Blanking
Timeout Period
From continuous current-limit condition to
FAULT_ assertion
10
7.5
0.5
35
35
4.0
3
ms
ms
ms
ms
Short-Circuit Blanking Timeout
Period
From short-circuit current-limit condition to
FAULT_ assertion
R
= 10Ω, does not include rise time
OUT_
Turn-On Delay
(from ON_ to 10% of V _)
OUT
R
= 10Ω, does not include fall time (from
OUT_
Turn-Off Delay from ON
ON_ to 90% of V _)
OUT
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
V
V
V
_ = 4V to 5.5V
2
V
V
IN
_ = 4V to 5.5V
0.8
1
IN
= 0 or V
-1
µA
V
ON_
SINK
IN_
FAULT_ Output Low Voltage
I
= 1mA, V _ = 4V
0.4
IN
FAULT_ Output High Leakage
Current
V
_ = V
= 5.5V
FAULT_
1
µA
IN
Autoreset OUT_ Current
Autoreset Threshold
In latched-off state, V
_ = 0
10
0.4
10
50
0.6
35
mA
V
OUT
In latched-off state, rising
In latched-off state, V
Autoreset Blanking Time
_ > 0.5V
ms
OUT
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.
_______________________________________________________________________________________
3
Dual USB Switch with Fault
Blanking and Autoreset
Typical Operating Characteristics
(Circuit of Figure 1, V = V
= V
= 5V, ONA = ONB = GND, T = +25°C, unless otherwise noted.)
IN
INA
INB
A
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
QUIESCENT CURRENT
vs. TEMPERATURE
QUIESCENT CURRENT
vs. INPUT VOLTAGE
60
54
48
42
3.5
3.3
3.1
2.9
2.7
2.5
55
53
51
49
47
45
V
= V
= V _
ONB IN
ONA
V
_
= 5.5V
IN
36
30
V
_
= 5V
IN
24
18
12
6
V
_
= 4.5V
IN
0
-40
-15
10
35
60
85
0
1
2
3
4
5
6
-40
-15
10
35
60
85
TEMPERATURE (°C)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
CONTINUOUS CURRENT-LIMIT
THRESHOLD vs. TEMPERATURE
SWITCH OFF-LEAKAGE
vs. TEMPERATURE
NORMALIZED RON vs. TEMPERATURE
1000
100
1.50
1.25
1.00
0.75
0.50
940
930
920
910
900
V
= V
= V _
ONB IN
ONA
V
IN_ = 5.5V
10
1
V
IN_ = 5V
V
IN_ = 4.5V
0.1
0.01
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
TURN-OFF TIME
vs. TEMPERATURE
FAULT-BLANKING TIME
vs. TEMPERATURE
TURN-ON TIME
vs. TEMPERATURE
3.5
3.3
3.1
2.9
2.7
2.5
22.0
21.8
21.6
21.4
21.2
21.0
4.0
3.8
3.6
3.4
3.2
3.0
V
_ = 4.5V
IN
V
_ = 5V
IN
V
_ = 5.5V
IN
V
IN
_ = 4.5V
V
_ = 5V
IN
V
_ = 5V
IN
V
IN
_
= 5.5V
35
V
_
= 5.5V
-15
IN
V
_
IN
= 4.5V
-40
-15
10
35
60
85
-40
-15
10
60
85
-40
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Dual USB Switch with Fault
Blanking and Autoreset
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V = V
= V
= 5V, ONA = ONB = GND, T = +25°C, unless otherwise noted.)
IN
INA
INB
A
AUTORESET CURRENT
vs. INPUT VOLTAGE
AUTORESET CURRENT
vs. TEMPERATURE
FAULT_ OUTPUT LOW VOLTAGE
vs. TEMPERATURE
0.250
0.225
0.200
0.175
0.150
0.125
0.100
40
35
30
25
20
15
50
40
30
20
10
0
I
_ = 1mA
FAULT
T
= -40°C
A
V
_ = 5.5V
IN
V
_ = 5V
IN
T
= +25°C
A
V
_ = 4.5V
IN
T
= +85°C
A
V
_ = 5.5V
IN
V
_ = 5V
IN
V
_ = 4.5V
IN
3.6
4.4
5.2
6.0
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
OVERLOAD RESPONSE INTO 2.5Ω
OVERLOAD RESPONSE INTO 2.5Ω
(EXPANDED TIME SCALE)
SHORT-CIRCUIT RESPONSE INTO 0Ω
MAX1823 toc13
MAX1823 toc14
MAX1823 toc15
A
B
5V
0
5V
5V
0
A
A
B
B
0
C
C
D
C
D
0
0
0
0
0
0
D
10ms/div
C: V
500µs/div
C: V
10ms/div
C: V
A: V , 5V/div
, 5V/div
A: V , 5V/div
, 5V/div
FAULTA
IN_
B: V
FAULTA
, 1A/div
IN_
A: V _, 5V/div
, 5V/div
FAULTA
IN
, 5V/div D: I
B: V
, 5V/div
D: I
, 1A/div
OUTA
OUTA
OUTA
OUTA
B: V
, 5V/div
D: I
, 1A/div
OUTA
OUTA
SHORT-CIRCUIT RESPONSE INTO 0Ω
SWITCH TURN-ON TIME
(EXPANDED TIME SCALE)
MAX1823 toc17
MAX1823 toc16
A
5V
A
0
B
0
5V
C
B
D
0
0
1ms/div
500µs/div
A: V , 5V/div
ONA
A: V , 5V/div
C: V
, 5V/div
B: V
, 2V/div
IN_
OUTA
FAULTA
OUTA
B: V
, 5V/div
D: I
, 2A/div
OUTA
_______________________________________________________________________________________
5
Dual USB Switch with Fault
Blanking and Autoreset
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V = V
IN
= V
= 5V, ONA = ONB = GND, T = +25°C, unless otherwise noted.)
INA
INB
A
STARTUP TIME
(TYPICAL USB APPLICATION)
SWITCH TURN-OFF TIME
MAX1823 toc18
MAX1823 toc19
A
B
0
A
B
0
5V
C
D
0
0
0
1ms/div
500µs/div
C: V , 2V/div
OUTA
A: V , 5V/div
A: V , 5V/div
ONA
OUTA
ONA
B: V
, 2V/div
B: V
, 5V/div
D : I
, 0.5A/div
FAULTA
OUTA
Pin Description
PIN
NAME
FUNCTION
1
ONA
Control Input for Switch A. Can be driven higher than IN_ without damage. A logic low turns switch A on.
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.
2, 3, 4
Control Input for Switch B. Can be driven higher than IN_ without damage. A logic low turns switch
B on.
5
6
ONB
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.
FAULTB
Power Output for Switch B. Connect a 1µF capacitor from OUTB to ground. Load condition may
require additional bulk capacitance.
7
8
9
OUTB
GND
Ground
Power Output for Switch A. Connect a 1µF capacitor from OUTA to ground. Load condition may
require additional bulk capacitance.
OUTA
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.
10
FAULTA
6
_______________________________________________________________________________________
Dual USB Switch with Fault
Blanking and Autoreset
can also be reset from fault manually by toggling ON_
for that channel.
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.)
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.
The MAX1823 operates from a 4V to 5.5V input voltage
range and guarantees a minimum 500mA 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.
Fault Indicators
The MAX1823 provides an open-drain fault output
(FAULT_) for each switch. For most applications, con-
nect FAULT_ to IN_ through a 100kΩ pullup resistor.
FAULT_ goes low when any of the following conditions
occur:
Use of low R
NMOS switches enables the MAX1823
ON
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.
•
•
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.
•
•
Undervoltage Lockout and
Input Voltage Requirements
The switch is in autoreset mode.
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
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.
is inhibited when V
is less than 3.4V.
IN_
Output Fault Protection
The MAX1823 senses the switch output voltage and
selects continuous current limiting when V
is
OUT
greater than 1V or short-circuit current limiting when
is less than 1V. When V is greater than 1V,
V
OUT
OUT
USB
INA
IN
OUTA
the device operates in a continuous current-limit mode
that sets the output current limit to 0.9A. When V is
PORT A
1µF*
OUT
INPUT
4.0V TO 5.5V
INB
less than 1V, the device operates in short-circuit cur-
0.1µF
rent-limit mode, sourcing 0.35A
the load.
current pulses to
RMS
100kΩ
MAX1823
USB
100kΩ
Autoreset Mode
FAULTA
FAULTB
OUTB
PORT B
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
1µF*
ONA
ONB
ONA
ONB
GND
* USB APPLICATIONS MAY REQUIRE
ADDITIONAL BULK CAPACITANCE.
Figure 1. Typical Application Circuit
_______________________________________________________________________________________
7
Dual USB Switch with Fault
Blanking and Autoreset
the device, the MAX1823 has an independent fault-
Behavior During Current Limit
and Fault Blanking
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.
The MAX1823 limits switch current in three ways. When
ON_ is high, the switch is off and leakage dominates
the residual output current. When ON_ is low, the
switch supplies a continuous output current of at least
500mA. When the output current exceeds the 0.9A
threshold, the MAX1823 limits the current depending
on the output voltage. For V
greater than 1V (cur-
OUT_
rent-limit mode), the MAX1823 regulates the output cur-
rent to 0.9A. For V less than 1V (short-circuit
OUT_
mode), the MAX1823 pulses the switch, decreasing the
current to 0.35A (Table 1). Note that a thermal over-
load may result from either of these high-current condi-
tions.
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
power source. No fault is indicated if the switch is able
to bring up the load within the 20ms blanking period.
RMS
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
INA
FAULTA
INA
ONA
CHARGE
PUMP
ILIM
BIAS
OUTA
1µF
25mA
THERMAL
SHUTDOWN
UVLO
REF
FAULT
LOGIC
GND
4.0V TO 5.5V
IN_
25mA
ILIM
TIMER
20ms
OSC
0.1µF
25kHz
OUTB
1µF
MAX1823
CHARGE
PUMP
ONB
INB
INB
FAULTB
Figure 2. Functional Diagram
_______________________________________________________________________________________
8
Dual USB Switch with Fault
Blanking and Autoreset
Table 1. MAX1823 Current Limiting and Fault Behavior
CONDITION
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.
Output Short Circuit
(V
OUT
< 1V)
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 I
(0.9A), and FAULT_ stays high until the
LIM
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.
Output Overload Current
(V > 1V)
•
•
OUT
•
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.
Thermal Fault
(T > +160oC)
J
•
An output voltage above 0.5V for 20ms resets the switch, turns on the output, and forces
FAULT_ high.
current limit. There is no limit to the output capacitor
Applications Information
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).
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.
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.
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
_______________________________________________________________________________________
9
Dual USB Switch with Fault
Blanking and Autoreset
For a 5V input and 1V output, the maximum power dis-
sipation per switch is:
P = (1.2A) ( 5V - 1V) = 4.8W
Turn-On and Turn-Off Behavior
In the absence of faults, the MAX1823’s internal switch-
es turn on and off slowly under the control of the ON_
inputs. Transition times for both edges are approxi-
mately 2ms. The slow charge-pump switch drive mini-
mizes load transients on the upstream power source.
Under thermal fault and UVLO, the power device turns
off rapidly (100ns) to protect the power device.
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.
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.
A short circuit at the output causes the power dissipat-
ed 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 V
= 5V, calculate the power dissipation for a
IN_
While the switches are on, power dissipation is small,
short-circuited output as follows:
and the package temperature change is minimal.
P = (0.025A)(5) = 0.125W
Calculate the power dissipation for this condition as fol-
lows:
2
P = (I
) R
OUT_
ON
For the normal operating current (I
= 0.5A), and
OUT_
Chip Information
the maximum on-resistance of the switch (135mΩ), the
TRANSISTOR COUNT: 3227
power dissipation is:
PROCESS: BiCMOS
2
P = (0.5A) x 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 = (I ) (V - V )
OUT
LIM
IN
10 ______________________________________________________________________________________
Dual USB Switch with Fault
Blanking and Autoreset
Package Information
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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