Philips Semiconductors ISP1520
Hi-Speed USB hub controller
Product data Rev. 03 — 24 November 2004 42 of 51
9397 750 13701 © Koninklijke Philips Electronics N.V. 2004. All rights reserved.
17. Application information

17.1 Descriptor configuration selection

17.2 Overcurrent detection limit adjustment

For an overcurrent limit of 500 mA per port, a PMOS with RDSON of approximately

100 mΩ is required. If a PMOS with a lower RDSON is used, analog overcurrent

detection can be adjusted by using a series resistor; see Figure 18.

∆VPMOS =∆Vtrip =∆Vtrip(intrinsic) −(IOC(nom) ×Rtd), where:

∆VPMOS = voltage drop on PMOS

IOC(nom) = 0.6 µA.

The I2C-bus cannot be shared between the EEPROM and the external microcontroller; see Table 1 1.(1) The function on port 4, which is a non-removable port, is optional.
Fig 17. Descriptors configuration selection application diagram.
004aaa303
ISP1520
ROM
external microcontroller
acting as I
2
C-bus master
USB function
EEPROM
I
2
C-bus
4 USB downstream facing ports
green and
amber LEDs,
port 1
green and
amber LEDs,
port 2
green and
amber LEDs,
port 3
green and
amber LEDs,
port 4(1)
upstream
facing port GoodLink
(1) Rtd is optional.
Fig 18. Adjusting analog overcurrent detection limit (optional).
004aaa259
VREF(5V0)
Rtd(1)
5 V
ISP1520
OCn_N
PSWn_N
IOC