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MAX1922
1A Current-Limited Switch for 2 USB Ports
MAX1922
1A Current-Limited Switch for 2 USB Ports
Typical Operating Circuit19-2254; Rev 1; 12/02
Pin Configuration
Ordering Information
General DescriptionThe MAX1922 current-limited 70mΩswitch 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 (16µA) and standby
current (1µA) conserve battery power in portable appli-
cations. 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 OCsignal 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 pro-
tection limits power dissipation and junction tempera-
ture. The device also has accurate internal current-
limiting 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 (-40°C to
+85°C) temperature range.
ApplicationsNotebook Computers
USB Ports
USB Hubs
Docking Stations
FeaturesAccurate Current Limit (1.4A min, 2.1A max)10ms Internal OCBlanking TimeoutOC
Blanking During Power-Up125mΩmax High-Side MOSFETShort-Circuit and Thermal Protection with
Overcurrent Logic Output
Undervoltage Lockout16µA Quiescent Supply Current1µA (max) Standby Supply Current2.7V to 5.5V Supply RangeUL Recognized: UL# E211935
MAX1922
1A Current-Limited Switch for 2 USB Ports
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= 5V, TA= 0°C to +85°C,unless otherwise noted. Typical values are at TA= +25°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.
IN, EN, OCto 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= +70°C)
8-Pin SO (derate 5.88mW/°C above +70°C)................471mW
Operating Temperature Range (extended).........-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX1922
1A Current-Limited Switch for 2 USB Ports
ELECTRICAL CHARACTERISTICS
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 5V, TA= 0°C to +85°C,unless otherwise noted. Typical values are at TA= +25°C.)
MAX1922
1A Current-Limited Switch for 2 USB Ports
Typical Operating Characteristics
(Circuit of Figure 2, VIN= 5V, TA = +25°C, unless otherwise noted.)
MAX1922
1A Current-Limited Switch for 2 USB Ports
2ms/div
MAX1922 toc10CURRENT-LIMIT AND OC RESPONSE
VIN AC-COUPLED
100mV/div
VOUT, 5V/div
VOC, 5V/div
IOUT, 1A/div
4µs/div
MAX1922 toc11CURRENT-LIMIT RESPONSE
VIN AC-COUPLED
500mV/div
VOUT, 5V/div
IOUT, 2A/div
VOC, 5V/div
20µs/div
MAX1922 toc12SWITCH TURN-ON TIME
VOUT, 5V/div
IOUT,
500mA/div
VOC, 5V/div
VEN, 5V/div
1µs/div
MAX1922 toc13SWITCH TURN-OFF TIME
VOUT, 5V/div
IOUT,
500mA/div
VOC, 5V/div
VEN, 5V/div
STARTUP TIME
(TYPICAL USB APPLICATION)
MAX1922 toc14
1ms/div
VOUT 5V/div
VEN 5V/div
IIN 1A/div
VOC 5A/div
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN= 5V, TA = +25°C, unless otherwise noted.)
MAX1922
1A Current-Limited Switch for 2 USB Ports
Detailed Description
The MAX1922 P-channel MOSFET power switch limits
output current to 1.4A min and 2.1A max. When the out-
putcurrent increases beyond the current limit (ILIMIT),
the current also increases through the replica switch
(IOUT/ 13000). The current-limit error amplifier com-
pares 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.
Continuous Short-Circuit Protection
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 OCoutput goes low immediate-
ly (no overcurrent blanking) when the junction tempera-
ture exceeds +165°C. When the MAX1922 cools 20°C,
the switch turns back on. If the fault short-circuit condi-
tion is not removed, the switch will cycle on and off,
resulting in a pulsed output.Indicator
The MAX1922 provides an overcurrent output (OC). A
100kΩpullup resistor from OCto 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 +165°C.The device is in current limit for greater than 10ms.
OC Blanking
The MAX1922 features 10ms overcurrent blanking.
Blanking allows brief current-limit faults, including
momentary short-circuit faults that occur when hot-
swapping a capacitive load, and ensures that no OCis
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 over-
current blanking timeout, the OCoutput 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
