PRELIMINARY
CM3503
CALIFORNIA MICRO DEVICES
USB 5V Single 1.4A Overcurrent Switch
Features
Pin Diagram
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•
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High-side high current switch with active low Enable
Very low on-resistance switch (0.07? typ.)
Up to 1.4A continuous current on the output
Over-current limits at 1.4A min
10msec min fault blanking delay on OC# output
prevents false overcurrent alarms
GND
VCC
VOUT
VOUT
VOUT
OC#
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Prevents backdrive current when host powered off
Low operating current (95µA typ.)
Low quiescent current when disabled (<1µA max)
Small 8-Lead SOIC package
VCC
EN#
Applications
SOIC-8
•
2 USB ports 5V supply overcurrent protection
Product Description
Typical Application Circuit
California Micro Devices’ CM3503 is a USB
overcurrent power switch that provides power to two
USB ports. The device has a very low on-resistance
power switch that provides the VBUS voltage at the
USB output ports with minimal voltage drop. When
the EN# pin is logic low, the power switch is ON,
and VCC is connected to the output VOUT. When the
EN# pin is logic high, the power switch is OFF, and
no power is available at the output.
GND
VOUT
VOUT
VOUT
OC#
VBUS
VCC
VCC
1 USB Port
1 USB Port
VCC
VBUS
EN#
The power switch has full over-current protection.
Whenever the current limit of the switch is
exceeded, the device enters a constant-current
mode, where the output voltage is progressively
reduced to prevent the current from increasing
further. The OC# output becomes active low only if
the overcurrent condition exceeds at least 10ms.
This fault blanking delay prevents false alarms from
being reported to the host USB controller.
Simplified Electrical Schematic
If the overcurrent condition is severe enough that
the part heats up to the thermal limit TMAX, then the
switch will be turned off and the temperature cools
down. At TMIN the switch then turns on again, and
the device heats up again, and so on, until the fault
is removed.
EN#
VCC
Over
current
protect
VOUT
OC#
The CM3503 also prevents backdrive current
flowing into the host from the connected peripheral.
This can occur when VCC is removed as the host
powers down, and the peripheral still has normal
power applied. The 5V from the peripheral can
therefore be linked to the host’s VBUS, potentially
causing backdrive current into the host and
overloading the peripheral power supply.
© 2003 California Micro Devices Corp. All rights reserved.
C0970500
09/10/03
430 N. McCarthy Blvd, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
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