Port power switch transistors, Overcurrent circuit detection, Power supply – Philips UM10011 User Manual

Page 8

Philips Semiconductors

UM10011_4

ISP1521 Hi-Speed USB Hub Demo Board

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