CALIFORNIA MICRO DEVICES
PRELIMINARY
CM3501
Dual USB Overcurrent Switch 750mA (V
CC
) / 100mA (V
SBY
)
Features
•
•
•
•
•
•
•
•
•
•
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Dual outputs, each with independent over-current
protection circuitry and indicator
Supports standby mode in PCs so that a peripheral
can ramp down safely to a current <100mA
Low ON-resistance switches
Up to 750mA (V
CC
) / 100mA (V
SBY
) continuous
current on each output
Over-current limits at 750mA / 100mA respectively
10msec min fault blanking delay on OC# outputs
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
PC motherboards with USB ports (i.e., can use a
CM3501 for 2 ports or 2 CM3501s for 4 ports, etc)
The CM3501 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.
Pin Diagram
GND
V
CC
V
SBY
SEL
SOIC-8
OC1#
V
OUT1
V
OUT2
OC2#
Applications
Typical Application Circuit
Product Description
California Micro Devices’ CM3501 is a dual port
USB overcurrent power switch that selects between
two independent 5V inputs available on a PC,
depending on the state of a logic input (SEL). The
device has two pairs of power switches, and each
pair is an analog “OR” function, providing a
continuous voltage at both outputs during power
transfer beween inputs.
V
CC
is the main 5V supply, which can be disabled in
a PC, and V
SBY
is the 5V standby supply which is
powered up whenever the PC has power. When the
‘SEL’ pin is at logic high, V
CC
is the assigned input
power supply. When ‘SEL’ is at logic low, V
SBY
is
used to power the output, and no current is taken
from V
CC
. Both switches can be deselected and
switched off by not driving (floating) the ‘SEL’ input,
which places the chip in low power mode.
Both pairs of switches have over-current protection.
Depending on whether ‘SEL’ is high or low, a current
over 750mA or 100mA respectively out of either
output causes the device to enter a constant-current
mode, where the output voltage is progressively
reduced to prevent the current from increasing
further. Each output is independent of the other, so if
one of the switches is switched on but is not in
overcurrent mode then it will remain switched on.
The OC# output becomes active only if the
overcurrent condition exceeds a minimum
continuous duration of 10ms.
If the overcurrent condition is severe enough that
the part heats up to the thermal limit T
MAX
, the switch
turns off and the temperature cools down to T
MIN
.
The switch then turns on again, and the device
heats up again, and so on, until the fault is removed.
© 2002 California Micro Devices Corp. All rights reserved.
GND
5V V
CC
5V V
SBY
Select V
CC
V
CC
V
SBY
SEL
OC1#
V
OUT1
V
OUT2
V
BUS
OC2#
V
BUS
1 USB Port
1 USB Port
Simplified Electrical Schematic
V
CC
SEL
V
SBY
750mA
Over
current
100mA
Over
current
750mA
Over
current
100mA
Over
current
OC1#
V
OUT1
OC2#
V
OUT2
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 ]
