SC2041

© 2000 SEMTECH CORP.

HotSwitch™ USB Power Distribution

Switch With Shutdown

July 18, 2000

652 MITCHELL ROAD NEWBURY PARK CA 91320

11

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

J

> 150°C, thus

activating the thermal shutdown circuitry.

TC

•

=

°

85

130

0 0375

90

.

U2

SC5205-3.3

1

2

3

4

5

VIN

GND

EN

BYP

VO

U3

SC2041

1

2

3

4

5

6

7

8

GND

IN

IN

SHDN

FLG

OUT

OUT

OUT

Downstream Port

VBUS

D+

D-

GND

Upstream Port

D+

D-

VBUS

GND

C2

10nF

C3

4.7uF

C1

4.7uF

Ferrite Bead

Ferrite Bead

C4

0.1uF

C5

33uF

USB Controller

D0D+

D0D-

VCC

EN

OC

D1D+

D1D-

R1

100k

5V Power Supply

+5V

GND

U4

SRDA05-4

I/O1

I/O2

I/O3

I/O4

REF2

REF2

REF1

REF1

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

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.

TYPICAL APPLICATIONS CIRCUITS

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.

APPLICATIONS INFORMATION (Cont.)

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-.