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Philips Semiconductors
UM10011_4
ISP1521 Hi-Speed USB Hub Demo Board
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
User manual Rev. 04.00 — 17 June 2004 8 of 20
5.5. Port Power Switch Transistors
The hub switches on or off the bus power to each downstream facing port through a low ohmic
PMOS transistor.
5.6. Overcurrent Circuit Detection
The integrated analog overcurrent detection circuit of the ISP1521 senses the voltage drop
across the power switch. When the port draws too much current, the voltage drop across the
power switch exceeds the trip voltage threshold. The overcurrent circuit detects this and
automatically switches off the power switch. More information on choosing the switch and
trimming the overcurrent detection voltage can be found in the ISP1521 Hi-Speed Universal Serial
Bus hub controller data sheet.
5.7. Power Supply
To power up the hub, plug the power supply into the power supply socket (PWR_C1).
Jumper J15 will set the powering mode in the hub’s descriptors as self-powered hub; see
Table 5-2.
Table 5-2: Setting the Power Mode Using J15
*—Default settings.
J15 Power Mode Logic State
OFF Self* 1 (HIGH)
J15