CALIFORNIA MICRO DEVICES
USB 5V Single 1.4A Overcurrent Switch
Features
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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
Prevents backdrive current when host powered off
Low operating current (95µA typ.)
Low quiescent current when disabled (<1µA max)
Small 8-Lead SOIC package
PRELIMINARY
CM3503
Pin Diagram
GND
V
CC
V
CC
EN#
SOIC-8
V
OUT
V
OUT
V
OUT
OC#
Applications
2 USB ports 5V supply overcurrent protection
Product Description
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 V
BUS
voltage at the
USB output ports with minimal voltage drop. When
the EN# pin is logic low, the power switch is ON,
and V
CC
is connected to the output V
OUT
. When the
EN# pin is logic high, the power switch is OFF, and
no power is available at the output.
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.
If the overcurrent condition is severe enough that
the part heats up to the thermal limit T
MAX
, then the
switch will be turned off and the temperature cools
down. At T
MIN
the switch then turns on again, and
the device heats up again, and so on, until the fault
is removed.
The CM3503 also prevents backdrive current
flowing into the host from the connected peripheral.
This can occur when V
CC
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 V
BUS
, potentially
causing backdrive current into the host and
overloading the peripheral power supply.
Typical Application Circuit
GND
V
CC
V
CC
V
CC
EN#
V
OUT
V
OUT
V
OUT
OC#
V
BUS
V
BUS
1 USB Port
1 USB Port
Simplified Electrical Schematic
EN#
V
CC
Over
current
protect
V
OUT
OC#
© 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
1
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
