
October 1998
5
Application Note 17
Application Note 17
Individual- and Ganged-Port Switching
Individual-port switching offers several advantages over
ganged-port switching. If a fault should occur on one port, the
other ports remain unaffected, while a ganged-port switch
would disable all ports. Individual-port control also offers
superior transient droop performance since ports have isola-
tion from each other. Individual-port control advantages
apply to both self-powered and bus-powered hubs.
Micrel
Individual Port Control
Figure 6 in the circuit examples section shows a self-powered
hub using two MIC2526 dual 500mA switches to control four
individual ports. If the USB controller has a single output
enable or overcurrent detection pin, the respective inputs or
outputs may have a common connection. An external digital
latch on each enable pin could be used to disable individual
ports during an overcurrent condition, allowing the other ports
to continue to operate.
ON/OFF
OVERCURRENT
MIC2526
3.3V USB Controller
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
10k
MIC5203-3.3
MIC5207-3.3
LDO Regulator
IN
OUT
GND
33μF*
Ferrite
Bead
4.45V to 5.25V
3.5A max.
(–)
V
BUS
D+
D–
GND
D+
D–
V+
ENA
FLGA
FLGB
ENB
OUTA
IN
GND
OUTB
Bold
lines indicate
0.1" wide, 1-oz. copper
high-current traces.
Downstream
USB
Port 1
500mA max.
Downstream
USB
Port 2
500mA max.
33μF*
0.1
μF
MIC2526
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
33μF*
ENA
FLGA
FLGB
ENB
OUTA
IN
GND
OUTB
Downstream
USB
Port 3
500mA max.
Downstream
USB
Port 4
500mA max.
33μF*
0.1
μF
0.01μF
0.01μF
0.01μF
0.01μF
4.7
μF
1.0
μF
GND
(+)
33μF
0.1
μF
10k
* 33μF, 16V tantalum or 100μF, 10V electrolytic per port
Figure 6. Regulated-Input Self-Powered Hub
ON/OFF
OVERCURRENT
3.3V USB Controller
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
MIC5203-3.3
MIC5207-3.3
LDO Regulator
IN
OUT
GND
33μF
Ferrite
Bead
V
BUS
D+
D–
GND
D+
D–
V+
Bold
lines indicate
0.1" wide, 1-oz. copper
high-current traces.
Downstream
USB
Port 1
4.75V min
500mA max.
33μF
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
33μF
33μF
0.01μF
0.01μF
0.01μF
0.01μF
4.7
μF
1.0
μF
GND
33μF
5.4V
20VA
IN
EN
OUT
FLAG
GND
MIC29301-5.0
LDO Regulator
5.4V
5.0V
10k
47μF
10k
Downstream
USB
Port 2
4.75V min
500mA max.
Downstream
USB
Port 3
4.75V min
500mA max.
Downstream
USB
Port 4
4.75V min
500mA max.
100mA
max.
Figure 5. Simple Stand-Alone Self-Powered Hub