Philips Semiconductors ISP1521
Hi-Speed USB hub controller
Product data Rev. 03 — 24 November 2004 44 of 53
9397 750 13702 © Koninklijke Philips Electronics N.V. 2004. All rights reserved.
17. Application information17.1 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 7, which is a non-removable port, is optional.Fig 17. Descriptors configuration selection application diagram.
004aaa302
ISP1521 ROM
external microcontroller
acting as I2C-bus master
USB function
EEPROM
I2C-bus
green and
amber LEDs,
port 1
green and
amber LEDs,
port 7(1)
7 USB downstream facing ports
. .
upstream
facing port GoodLink
(1) Rtd is optional.Fig 18. Adjusting analog overcurrent detection limit (optional).
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VREF(5V0)
Rtd(1)
5 V
ISP1521OCn_NPSWn_N
IOC