SC2041 Semtech Corporation, SC2041 Datasheet - Page 11

• Manufacturer Part Number: SC2041
• Description: HotSwitch USB Power Distribution Switch With Shutdown
• Manufacturer: Semtech Corporation

T
July 18, 2000
APPLICATIONS INFORMATION (Cont.)
power planes) and P
worst-case T
Thus it can be seen that this device does not require
any additional copper area for heatsinking under
normal operating conditions. Sustained overcurrents or
short circuits will rapidly heat T
activating the thermal shutdown circuitry.
TYPICAL APPLICATIONS CIRCUITS
Self-Powered Hub, Individual Port Power
Management:
A self-powered hub must supply a continuous 500mA
of current to each downstream port. Since an internal
power supply is used to supply the power, self-powered
hubs are required to implement overcurrent protection
for safety. The self-powered hub must also have a
method to detect and report fault conditions to the USB
controller. The circuit below utilizes the SC2041 to
provide individual port overcurrent protection & power
switching for maximum port protection. Under fault
conditions, the SC2041 provides the short-circuit
current limiting function and has a fault flag logic output
Notes:
(1) One port only shown for simplicity.
(2) 33µF output capacitor assumes four downstream ports for this hub, therefore meeting the USB specification
requirement of 120µF minimum capacitance per hub.
(3) The SRDA05-4 shown would also protect lines D2D+ and D2D-.
© 2000 SEMTECH CORP.
J
5V Power Supply
Upstream Port
VBUS
GND
GND
+5V
85
D+
D-
130 0 0375
J
to be:
C1
4.7uF
.
D(MAX)
1
2
3
U2
SC5205-3.3
VIN
GND
EN BYP
90
VO
= 37.5mW, we calculate the
C
5
4
C2
10nF
J
C3
4.7uF
> 150°C, thus
D0D+
D0D-
VCC
USB Controller
HotSwitch™ USB Power Distribution
Switch With Shutdown
D1D+
D1D-
EN
OC
R1 100k
C4
0.1uF
Layout Considerations
The ceramic bypass capacitors for IN and OUT should
be connected as close to the relevant device pins as
possible. The bulk output capacitors required by the
USB specification should be placed close to the USB
connector to provide a low impedance source for hot
plug purposes. Ferrite beads should be placed on the
V
reduce the droop on adjacent ports during hot plug
events.
for notifying the hub controller. The USB hub can use
the SC2041 to remove power from the faulty port,
allowing the other ports to operate normally.
Since USB is a hot insertion and removal system, USB
ports are subject to electrostatic discharge (ESD). The
SRDA05-4 provides ESD protection on the downstream
data and power lines. Each device will protect two USB
ports. With proper layout the port is hardened to greater
than 15kV, meeting the requirements of IEC 1000-4-2.
The SC5205 LDO regulator is used to power the hub
controller from the hub’s 5V power supply.
BUS
652 MITCHELL ROAD NEWBURY PARK CA 91320
1
2
3
4
U3
and Ground pins of the downstream connectors to
GND
IN
IN
SHDN
SC2041
OUT
OUT
OUT
FLG
U4
SRDA05-4
I/O1
I/O2
I/O3
I/O4 REF2
8
7
6
5
REF1
REF1
REF2
C5
33uF
SC2041
Ferrite Bead
Ferrite Bead
Downstream Port
VBUS
D+
D-
GND
11