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Philips Semiconductors
ISP1521
Hi-Speed USB hub controller
Product data Rev. 03 — 24 November 2004 14 of 53
9397 750 13702
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
9.1 Configuration through I/O pins
9.1.1 Number of downstream facing ports
To discount a physical downstream facing port, connect pins DP and DM of that
downstream facing port to V
CC
(3.3 V) starting from the highest port number (7); see
Table 4.
The sum of physical ports configured is reflected in the bNbrPorts field.
9.1.2 Power switching
Power switching of downstream ports can be done individually or ganged, where all
ports are simultaneously switched with one power switch. The ISP1521 supports both
modes, which can be selected using input PSWn_N; see Tabl e 5 .
Voltage drop requirements: Self-powered hubs are required to provide a minimum
of 4.75 V to its output port connectors at all legal load conditions. To comply with
Underwriters Laboratory Inc. (UL) safety requirements, the power from any port must
be limited to 25 W (5 A at 5 V). Overcurrent protection may be implemented on a
global or individual basis.
Assuming a 5 V ± 3 % power supply, the worst-case supply voltage is 4.85 V. This
only allows a voltage drop of 100 mV across the hub Printed-Circuit Board (PCB) to
each downstream connector. This includes a voltage drop across the:
• Power supply connector
• Hub PCB (power and ground traces, ferrite beads)
• Power switch (FET on-resistance)
• Overcurrent sense device.
The PCB resistance and power supply connector resistance may cause a drop of
25 mV, leaving only 75 mV as the voltage drop allowed across the power switch and
overcurrent sense device. The individual voltage drop components are shown in
Figure 5.
Table 4: Downstream facing port number pin configuration
Number of physical
downstream facing port
DM1/DP1 DM2/DP2 DM3/DP3 DM4/DP4 DM5/DP5 DM6/DP6 DM7/DP7
715kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
615kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
V
CC
515kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
V
CC
V
CC
415kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
V
CC
V
CC
V
CC
315kΩ
pull-down
15 kΩ
pull-down
15 kΩ
pull-down
V
CC
V
CC
V
CC
V
CC
215kΩ
pull-down
15 kΩ
pull-down
V
CC
V
CC
V
CC
V
CC
V
CC