CALIFORNIA MICRO DEVICES
PRELIMINARY
CM3511
Dual USB Overcurrent Switch 1.2A (V
CC
) / 200mA (V
SBY
)
Features
•
•
•
•
•
•
•
•
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
Up to 1.2A (V
CC
) / 200mA (V
SBY
) continuous
current on each output
Over-current limits at 1.2A / 200mA 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.)
Small 8-Lead SOIC package
PC motherboards, Notebooks, Set-Top-Boxes
The CM3511 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
TOP
SOIC-8
OC1#
V
OUT1
V
OUT2
OC2#
Applications
•
Typical Application Circuit
Product Description
California Micro Devices’ CM3511 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 between 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.
GND
5V V
CC
5V V
SBY
Select V
CC
V
CC
V
SBY
SEL
OC1#
V
OUT1
V
OUT2
OC2#
V
BUS
V
BUS
2 USB Ports
2 USB Ports
Simplified Electrical Schematic
CP
H Over
current
protect
L Over
current
protect
H Over
current
protect
L Over
current
protect
C0970500
Both pairs of switches have over-current protection.
Depending on whether ‘SEL’ is high or low, a current V
CC
over 1.2A or 200mA respectively out of either output
causes the device to enter a constant-current mode, SEL
where the output voltage is progressively reduced to
prevent the current from increasing further. Each V
SBY
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.
OC1#
V
OUT1
CP
OC2#
V
OUT2
11/10/03
430 N. McCarthy Blvd, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
1
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
