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19-2254; Rev 1; 12/02
1A Current-Limited Switch for 2 USB Ports
General Description
The MAX1922 current-limited 70m switch with built-in fault blanking provides an accurate, preset 1.4A to 2.1A current limit, making it ideal for dual USB applications. Its low quiescent supply current (16A) and standby current (1A) conserve battery power in portable applications. The MAX1922 operates with inputs from 2.7V to 5.5V, making it ideal for both 3V and 5V systems. An overcurrent signal (OC) notifies the microprocessor that the internal current limit has been reached. A 10ms overcurrent-blanking feature allows momentary faults (such as those caused when hot-swapping into a capacitive load) to be ignored, thus preventing false alarms to the host system. This blanking also prevents an OC signal from being issued when the device is powering up. The MAX1922 has several safety features to ensure that the USB port is protected. Built-in thermal-overload protection limits power dissipation and junction temperature. The device also has accurate internal currentlimiting circuitry to protect the input supply against overload. The MAX1922 is offered in a space-saving 8-pin SO package and operates over the extended (-40C to +85C) temperature range. 10ms Internal OC Blanking Timeout OC Blanking During Power-Up 125m max High-Side MOSFET Short-Circuit and Thermal Protection with Overcurrent Logic Output Undervoltage Lockout 16A Quiescent Supply Current 1A (max) Standby Supply Current 2.7V to 5.5V Supply Range UL Recognized: UL# E211935
Features
Accurate Current Limit (1.4A min, 2.1A max)
MAX1922
Ordering Information
PART MAX1922ESA TEMP RANGE -40C to +85C PIN-PACKAGE 8 SO
Applications
Notebook Computers USB Ports USB Hubs Docking Stations
Pin Configuration
TOP VIEW
INPUT 2.7V TO 5.5V
Typical Operating Circuit
IN GND IN IN 1 2 8 7 OUT OUT OUT OC ON OFF EN GND OC
OUT
OUTPUT
MAX1922
MAX1922
3 6 5 EN 4
SO
________________________________________________________________ Maxim Integrated Products
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1A Current-Limited Switch for 2 USB Ports MAX1922
ABSOLUTE MAXIMUM RATINGS
IN, EN, OC to GND...................................................-0.3V to +6V OUT to GND ................................................-0.3V to (VIN + 0.3V) Maximum Switch Current.........................2.3A (internally limited) OUT Short-Circuit to GND ..........................................Continuous Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.88mW/C above +70C)................471mW Operating Temperature Range (extended) .........-40C to +85C 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
(VIN = 5V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER OPERATING CONDITION Input Voltage POWER SWITCH Switch Static Drain-Source OnState Resistance Switch Turn-On Time Switch Turn-Off Time ENABLE INPUT (EN) EN High-Level Input Voltage EN Low-Level Input Voltage EN Input Current Startup Time CURRENT LIMIT Overload Output Current Short-Circuit Output Current SUPPLY CURRENT Supply Current, Low-Level Input Supply Current, High-Level Input Supply-Leakage Current UNDERVOLTAGE LOCKOUT Undervoltage Lockout OVERCURRENT (OC) OC Threshold OC Output Low Voltage VOL ISINK = 1mA, VIN = 3V 1.1 0.4 A V UVLO Rising edge, 100mV hysteresis 2.0 2.4 2.6 V IQ VEN = VIN = VOUT = 5.5V VEN = 0, IOUT = 0 VEN = VIN = 5.5V, VOUT = 0 Timer not running Timer running TA = +25C TA = 0C to +85C 0.002 16 35 0.01 2 15 1 25 A A A ILIMIT ISC Force VOUT to 4.5V OUT shorted to GND 1.4 1.75 1 2.1 1.4 A A VIH VIL VIN = 2.7V to 3.6V VIN = 3.7V to 5.5V VIN = 2.7V to 5.5V VEN = VIN or GND VIN = 5V, COUT = 150F from EN driven low to 50% full VOUT -1 1 2.0 2.4 0.8 1 V V A ms TA = +25C RDS(ON) tON tOFF TA = 0C to +85C ILOAD = 400mA ILOAD = 400mA 3 VIN = 4.4V to 5.5V VIN = 4.4V to 5.5V VIN = 3V 72 80 6 70 100 125 150 200 20 s s m VIN 2.7 5.5 V SYMBOL CONDITIONS MIN TYP MAX UNITS
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1A Current-Limited Switch for 2 USB Ports
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 5V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER OC Off-State Current OC Blanking Timeout Period THERMAL SHUTDOWN Thermal Shutdown Threshold 165 C tBL SYMBOL CONDITIONS VIN = VOC = 5V From overcurrent condition to OC assertion 6 10 MIN TYP MAX 1 13 UNITS A ms
MAX1922
ELECTRICAL CHARACTERISTICS
(VIN = 5V, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER OPERATING CONDITION Input Voltage POWER SWITCH Switch Static Drain-Source On-State Resistance Switch Turn-On Time Switch Turn-Off Time ENABLE INPUT (EN) EN High-Level Input Voltage EN Low-Level Input Voltage EN Input Current CURRENT LIMIT Overload Output Current Short-Circuit Output Current SUPPLY CURRENT Supply Current, Low-Level Input Supply Current, High-Level Input Supply Leakage Current UNDERVOLTAGE LOCKOUT Undervoltage Lockout OVERCURRENT (OC) OC Threshold OC Output Low Voltage OC Off-State Current OC Blanking Timeout Period tBL VOL ISINK = 1mA, VIN = 3V VIN = VOC = 5V From overcurrent condition to OC assertion 6 1.1 0.4 1 14 A V A ms UVLO Rising edge, 100mV hysteresis 2.0 2.9 V IQ VEN = VIN = VOUT = 5.5V VEN = GND, IOUT = 0, timer not running VEN = VIN = 5.5V, VOUT = GND 2 25 15 A A A ILIMIT ISC Force VOUT to 4.5V OUT shorted to GND 1.2 2.3 1.5 A A VIH VIL VIN = 3.0V to 3.6V VIN = 3.7V to 5.5V VIN = 3.0V to 5.5V VEN = VIN or GND -1 2.0 2.4 0.8 1 V V A RDS(ON) tON tOFF VIN = 4.4V to 5.5V VIN = 3V ILOAD = 400mA ILOAD = 400mA 1 125 150 200 20 m s s VIN 3.0 5.5 V SYMBOL CONDITIONS MIN TYP MAX UNITS
Note 1: Specifications to -40C are guaranteed by design, not production tested.
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1A Current-Limited Switch for 2 USB Ports MAX1922
Typical Operating Characteristics
(Circuit of Figure 2, VIN = 5V, TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX1922 toc01
QUIESCENT CURRENT vs. TEMPERATURE
MAX1922 toc02
OFF SUPPLY CURRENT vs. TEMPERATURE
EN = IN OUT = OPEN OFF SUPPLY CURRENT (nA) 10
MAX1922 toc03
20 18 QUIESCENT CURRENT (A) 16 14 12 10 8 6 4 2 0
VEN = 0 IOUT = 0
18.0 IOUT = 0 17.5 QUIESCENT CURRENT (A) 17.0 16.5 16.0 15.5 15.0 14.5 14.0 VIN = 3V VIN = 5V
100
1
0.1
0.01 -40 -15 10 35 60 85 -40 -15 TEMPERATURE (C) 10 35 TEMPERATURE (C) 60 85
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
OFF SWITCH CURRENT vs. TEMPERATURE
MAX1922 toc04
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
MAX1922 toc05
NORMALIZED OUTPUT CURRENT vs. OUTPUT VOLTAGE
ILIMIT(1.75A)
MAX1922 toc06
1000 EN = IN VOUT = 0 OFF SWITCH CURRENT (nA) 100
1.4 1.3 1.2 NORMALIZED RON 1.1 1.0 0.9 0.8 0.7 IOUT = 850mA
1.2 NORMALIZED OUTPUT CURRENT 1.0 0.8 0.6
10
1
SHORT-CIRCUIT CURRENT 0.4 0.2 0
0.1
0.6 0.5
0.01 -40 -15 10 35 TEMPERATURE (C) 60 85
0.4 -40 -15 10 35 60 85 TEMPERATURE (C)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT VOLTAGE (V)
TURN-ON TIME vs. TEMPERATURE
140 120 TURN-ON TIME (s) VIN = 3V 100 80 60 40 20 0 -40 -15 10 35 60 85 TEMPERATURE (C) VIN = 5V IOUT = 850mA COUT = 0.1F
MAX1922 toc07
TURN-OFF TIME vs. TEMPERATURE
MAX1922 toc08
OC BLANKING TIMEOUT vs. TEMPERATURE
14 OC BLANKING TIMEOUT (ms) 13 12 11 10 9 8 7 6 5 VIN = 3V OR 5V IOUT = 1.75A
MAX1922 toc09
160
9.0 8.5 8.0 TURN-OFF TIME (s) 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 -40 -15 10 35 60 VIN = 3V VIN = 5V IOUT = 850mA COUT = 0.1F
15
85
-40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
4
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1A Current-Limited Switch for 2 USB Ports
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = 5V, TA = +25C, unless otherwise noted.)
MAX1922
CURRENT-LIMIT AND OC RESPONSE
MAX1922 toc10
CURRENT-LIMIT RESPONSE
MAX1922 toc11
5V 5V VIN AC-COUPLED 100mV/div VOUT, 5V/div 0 VOC, 5V/div 0 IOUT, 1A/div 0 2ms/div 0 4s/div IOUT, 2A/div 0 5V VOUT, 5V/div VOC, 5V/div VIN AC-COUPLED 500mV/div
SWITCH TURN-ON TIME
MAX1922 toc12
SWITCH TURN-OFF TIME
MAX1922 toc13
VOUT, 5V/div 0 VEN, 5V/div 0 5V VOC, 5V/div
VOUT, 5V/div 0 VEN, 5V/div 0 5V VOC, 5V/div IOUT, 500mA/div 0 1s/div
IOUT, 500mA/div 0 20s/div
STARTUP TIME (TYPICAL USB APPLICATION)
MAX1922 toc14
0 FULL CURRENT LIMIT CHARGES CAPACITOR
VOUT 5V/div
VEN 5V/div 0 RESISTOR LOAD CURRENT 0 5V 1ms/div SHORT-CIRCUIT CURRENT LIMIT
IIN 1A/div VOC 5A/div
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1A Current-Limited Switch for 2 USB Ports MAX1922
Pin Description
PIN 1 2, 3 4 5 6, 7, 8 NAME GND IN EN OC OUT Ground Input. P-channel MOSFET source--connect all IN pins together and bypass with a 1F capacitor ground. Active-Low Switch Enable Input. A logic-low turns on the switch. Overcurrent-Indicator Output. This open-drain output goes low when the device is in thermal shutdown or undervoltage lockout, or during a sustained (10ms) current-limit condition. Switch Output. P-channel MOSFET drain--connect all OUT pins together and bypass with a 0.1F capacitor to ground. FUNCTION
Continuous Short-Circuit Protection
IN P OUT
MAX1922
OC P
The MAX1922 is a short-circuit-protected switch. In the event of an output short-circuit condition, the current through the switch is foldback-current-limited to 1A continuous.
Thermal Shutdown
The MAX1922 has a thermal shutdown feature. The switch turns off and the OC output goes low immediately (no overcurrent blanking) when the junction temperature exceeds +165C. When the MAX1922 cools 20C, the switch turns back on. If the fault short-circuit condition is not removed, the switch will cycle on and off, resulting in a pulsed output.
N
REPLICA AMPLIFIER ON P
ON
CURRENT-LIMIT AMPLIFIER 1.24V
OC Indicator
The MAX1922 provides an overcurrent output (OC). A 100k pullup resistor from OC to IN provides a logic control signal. This open-drain output goes low when any of the following conditions occur: * The input voltage is below the 2.4V undervoltage lockout (UVLO) threshold. * The die temperature exceeds the thermal shutdown temperature limit of +165C. * The device is in current limit for greater than 10ms.
10ms TIMER HOT EN CONTROL CIRCUITRY
GND
Figure 1. Functional Diagram
OC Blanking
Detailed Description
The MAX1922 P-channel MOSFET power switch limits output current to 1.4A min and 2.1A max. When the output current increases beyond the current limit (ILIMIT), the current also increases through the replica switch (IOUT / 13000). The current-limit error amplifier compares the voltage to the internal 1.24V reference and regulates the current back to the ILIMIT (Figure 1). These switches are not bidirectional; therefore, the input voltage must be higher than the output voltage.
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The MAX1922 features 10ms overcurrent blanking. Blanking allows brief current-limit faults, including momentary short-circuit faults that occur when hotswapping a capacitive load, and ensures that no OC is issued during power-up. When a load transient causes the device to enter current limit, an internal counter starts. If the load fault persists beyond the 10ms overcurrent blanking timeout, the OC output asserts low. Ensure that the MAX1922 input is adequately bypassed to prevent input glitches from triggering spurious OC outputs. Input voltage glitches less than 150mV will not
_______________________________________________________________________________________
1A Current-Limited Switch for 2 USB Ports
cause a spurious OC output. Load-transient faults less than 10ms (typ) will not cause an OC output assertion. Only current-limit faults are blanked. Die overtemperature faults and input voltage droops below the UVLO threshold will cause an immediate OC output. Under normal operating conditions, the package can dissipate and channel heat away. Calculate the maximum power dissipation as follows: P = (ILIMIT)2 RON where ILIMIT is the preset current limit (2.1A max) and RON is the on-resistance of the switch (125m max). When the output is short circuited, foldback-current limiting activates and the voltage drop across the switch equals the input supply voltage. The power dissipated across the switch increases, as does the die temperature. If the fault condition is not removed, the thermaloverload protection circuitry activates (see Thermal Shutdown section). Wide power-bus planes connected to IN and OUT and a ground plane in contact with the device help dissipate additional heat.
MAX1922
Applications Information
Input Capacitor
To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from IN to GND. A 1F ceramic capacitor will be adequate for most applications; however, higher capacitor values will further reduce the voltage drop at the input (Figure 2).
Output Capacitor
Connect a 0.1F capacitor from OUT to GND. This capacitor helps to prevent inductive parasitics from pulling OUT negative during turn-off.
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 MAX1922 is capable of driving inductive loads, but avoid exceeding the device's absolute maximum ratings. Usually the load inductance is relatively small, and the MAX1922 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 MAX1922 output below 6V and above -0.3V.
Layout and Thermal Dissipation
Important: Optimize the switch response time to output short-circuit conditions by keeping all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors as close as possible to the device (no more than 5mm away). All IN and OUT pins must be connected with short traces to the power bus. Wide power-bus planes will provide superior heat dissipation through the MAX1922's IN and OUT pins.
INPUT 1F 100k OVERCURRENT OUTPUT OFF ON
IN
OUT
OUTPUT 0.1F*
Chip Information
TRANSISTOR COUNT: 715 PROCESS: BiCMOS
MAX1922
OC
EN GND
*USB SPECIFICATIONS REQUIRE A HIGHER VALUE CAPACITOR.
Figure 2. Typical Application Circuit
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1A Current-Limited Switch for 2 USB Ports MAX1922
Package Information
SOICN .EPS
INCHES DIM A A1 B C e E H L MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050
MILLIMETERS MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 1.27
N
E
H
VARIATIONS:
1
INCHES
MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC
TOP VIEW
DIM D D D
MIN 0.189 0.337 0.386
MAX 0.197 0.344 0.394
D A e B A1 L C
0-8
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL DOCUMENT CONTROL NO. REV.
21-0041
B
1 1
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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