Philips UM10011 Port Power Switch Transistors, Overcurrent Circuit Detection, Power Supply

Philips Semiconductors	UM10011_4
	ISP1521 Hi-Speed USB Hub Demo Board

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

J15	Power Mode	Logic State
OFF	Self*	1 (HIGH)

*—Default settings.

J15

		© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
User manual	Rev. 04.00 — 17 June 2004	8 of 20