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PDF MAX1823A Data sheet ( Hoja de datos )
| Número de pieza | MAX1823A | |
| Descripción | Dual USB Switch | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-1903; Rev 3; 10/03
www.DataSheet4U.com
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 guar-
anteed to supply 720mA and meet USB specifications.
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
protection limits power dissipation and junction temper-
ature. Accurate internal current-limiting circuitry pro-
tects 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 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 (cur-
rent from OUT_ to IN_) while in shutdown.
The MAX1823 is available in a space-saving 10-pin
µMAX 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 ver-
sion of this device, refer to the MAX1946 data sheet. For
a triple version, refer to the MAX1940 data sheet.
Applications
USB Ports and Hubs
Notebook and Desktop Computers
PDAs and Palmtop Computers
Docking Stations
Pin Configuration
TOP VIEW
*(ONA) ONA 1
INA 2
IN 3
INB 4
*(ONB) ONB 5
MAX1823
MAX1823A
MAX1823B
MAX1823H
10 FAULTA
9 OUTA
8 GND
7 OUTB
6 FAULTB
µMAX
*( ) ARE FOR MAX1823B/MAX1823H.
Features
o Dual USB Switch in Tiny 10-Pin µMAX Package
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 50µA Quiescent Current (Both Switches On)
o 3µA Standby Current
o UL Recognized
PART
MAX1823EUB
MAX1823AEUB
MAX1823BEUB
MAX1823HEUB
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
10 µMAX
10 µMAX
10 µMAX
Typical Operating Circuit
INPUT
4V TO 5.5V
ONA
ONB
INA OUTA
IN
INB
MAX1823
MAX1823A
FAULTA
OUTB
FAULTB
ONA
ONB
GND
USB
PORT A
USB
PORT B
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
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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 = -40°C
to +85°C, 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
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
MIN TYP MAX UNITS
2V
0.8 V
-1 +1 µA
0.4 V
1 µA
Autoreset OUT_Current
Autoreset Threshold
Autoreset Blanking Time
In latched-off state, VOUT_ = 0V
In latched-off state, rising
In latched-off state, VOUT_ > 0.5V
10
0.4
10
50 mA
0.6 V
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.
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 = +25°C,
unless otherwise noted.)
QUIESCENT CURRENT
vs. INPUT VOLTAGE
60
54
48
42
36
30
24
18
12
6
0
0123456
INPUT VOLTAGE (V)
QUIESCENT CURRENT
vs. TEMPERATURE
55
VIN_ = 5.5V
53
51 VIN_ = 5V
49
VIN_ = 4.5V
47
45
-40
-15 10 35 60
TEMPERATURE (°C)
85
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
3.5
ON_ = IN_ (MAX1823/MAX1823A)
ON_ = GND (MAX1823B/MAX1823H)
3.3
3.1
2.9
2.7
2.5
-40
-15 10 35 60
TEMPERATURE (°C)
85
_______________________________________________________________________________________ 5
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Dual USB Switch with Fault
Blanking and Autoreset
Table 1. MAX1823 Current Limiting and Fault Behavior
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 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.
Thermal fault
(TJ > +160°C)
• A junction temperature of +160°C immediately forces FAULT_ low (the blanking timer does
not apply to thermal faults) and turns off the switch. The junction cooling 15°C 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.
Fault blanking allows the MAX1823 to handle USB loads
that may not be fully compliant with the USB specifica-
tions. USB loads with additional bypass capacitance
and/or large startup currents can be successfully pow-
ered 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.
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-circuit con-
ditions. A 0.1µF 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 larg-
er capacitance prevents voltage spikes from exceeding
the MAX1823’s absolute maximum ratings.
Output Capacitor
Place a 1µF 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 start-
up fault assertion, the capacitor must charge up within
the fault-blanking delay period. Typically, starting up into
a 330µF or smaller capacitor does not trigger a fault out-
put. 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 com-
monly 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 rat-
ings. Usually the load inductance is relatively small, and
the MAX1823’s input includes a substantial bulk capaci-
tance 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 out-
put below 6V and above -0.3V.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet MAX1823A.PDF ] | |
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