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 R
DSON
of approximately
100 mΩ is required. If a PMOS with a lower R
DSON
is used, analog overcurrent
detection can be adjusted by using a series resistor; see Figure 18.
∆V
PMOS
= ∆V
trip
= ∆V
trip(intrinsic)
− (I
OC(nom)
× R
td
), where:
∆V
PMOS
= voltage drop on PMOS
I
OC(nom)
= 0.6 µA.
The I
2
C-bus cannot be shared between the EEPROM and the external microcontroller; see Table 11.
(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) R
td
is optional.
Fig 18. Adjusting analog overcurrent detection limit (optional).
004aaa259
V
REF(5V0)
R
td
(1)
5 V
ISP1520
OCn_N
PSWn_N
I
OC
