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ISP1122 Datasheet(PDF) 25 Page - NXP Semiconductors

Part # ISP1122
Description  Universal Serial Bus stand-alone hub
PDF  48 Pages
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Manufacturer  PHILIPS [NXP Semiconductors]
Direct Link  http://www.nxp.com
Logo PHILIPS - NXP Semiconductors

ISP1122 Datasheet(HTML) 25 Page - NXP Semiconductors

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Philips Semiconductors
ISP1122
USB stand-alone hub
Product specification
Rev. 03 — 29 March 2000
25 of 48
9397 750 07002
© Philips Electronics N.V. 2000. All rights reserved.
The ISP1122 overcurrent detection circuit has been designed with a nominal trip
voltage (
∆V
trip) of 85 mV. This gives a typical trip current of approximately 850 mA for
a power switch with an on-resistance of 100 m
Ω1.
12.3 Tuning the overcurrent trip voltage
The ISP1122 trip voltage can optionally be adjusted through external components to
set the desired trip current. This is done by inserting tuning resistors at pins SP/BP or
OCn (see Figure 9). Rtu tunes up the trip voltage ∆Vtrip and Rtd tunes it down
according to Equation 1.
(1)
with Iref(nom) =5 µA and IOC(nom) = 0.5 µA.
12.4 Reference circuits
Some typical examples of port power switching and overcurrent detection modes are
given in Figure 10 to Figure 13.
The RC circuit (47 k
Ω and 0.1 µF) around the PMOS switch provides for soft turn-on.
The series resistor connecting the SP/BP pin to VCC tunes up the overcurrent trip
voltage slightly (see Figure 9). In the schematic diagram the resistor separates the
net names for pins VCC and SP/BP. This allows an automatic router to use a wide
trace for VCC and a narrow trace to connect pin SP/BP.
1.
The following PMOS power switches have been tested to work well with the ISP1122: Philips PHP109, Vishay Siliconix Si2301DS,
Fairchild FDN338P.
∆V
trip
∆V
trip intrinsic
()
I
ref
R
tu
⋅
I
OC
R
td
⋅
–
+
=
Iref(nom) =5 µA
IOC(nom) = 0.5 µA
IOC(nom) = 0.5 µA
a.
Self-powered mode.
b.
Bus-powered mode.
Fig 9.
Tuning the overcurrent trip voltage.
handbook, halfpage
MBL042
VCC
Iref
Rtu
Rtd
low-ohmic
PMOS switch
VCC SP/BP
ISP1122
OCn
IOC
handbook, halfpage
MBL043
VBUS
Rtd
low-ohmic
PMOS switch
VCC SP/BP
ISP1122
OCn
IOC



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