isp1122 NXP Semiconductors, isp1122 Datasheet - Page 25

• Manufacturer Part Number: isp1122
• Description: Isp1122 Universal Serial Bus Stand-alone Hub
• Manufacturer: NXP Semiconductors

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