isp1122 NXP Semiconductors, isp1122 Datasheet - Page 23

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

Philips Semiconductors
9397 750 07002
Product specification
Fig 6. Typical voltage drop components in self-powered mode using individual overcurrent detection.
Fig 7. Typical voltage drop components in self-powered mode using global overcurrent detection.
handbook, full pagewidth
handbook, full pagewidth
(1) Includes PCB traces, ferrite beads, etc.
(1) Includes PCB traces, ferrite beads, etc.
POWER SUPPLY
5.1 V KICK-UP
3% regulated
POWER SUPPLY
3% regulated
5 V
11.1.2 Bus-powered hubs
4.95 V(min)
Assuming a 5 V
allows a voltage drop of 100 mV across the hub printed-circuit board (PCB) to each
downstream connector. This includes a voltage drop across:
PCB resistance and power supply connector resistance may cause a drop of 25 mV,
leaving only 75 mV as the voltage drop allowed across the power switch and
overcurrent sense device. The individual voltage drop components are shown in
Figure
In case of global overcurrent detection an increased voltage drop is needed for the
overcurrent sense device (in this case a low-ohmic resistor). This can be realized by
using a special power supply of 5.1 V
Bus-powered hubs are guaranteed to receive a supply voltage of 4.5 V at the
upstream port connector and must provide a minimum of 4.4 V to the downstream
port connectors. The voltage drop of 100 mV across bus-powered hubs includes:
•
•
•
•
•
•
•
4.85 V(min)
Power supply connector
Hub PCB (power and ground traces, ferrite beads)
Power switch (FET on-resistance)
Overcurrent sense device.
Hub PCB (power and ground traces, ferrite beads)
Power switch (FET on-resistance)
Overcurrent sense device.
for overcurrent
sense resistor
voltage drop
low-ohmic
6.
detection
100 mV
ISP1122
power
switch
voltage drop
75 mV
3% power supply the worst case supply voltage is 4.85 V. This only
Rev. 03 — 29 March 2000
ISP1122
PMOS switch
switch
power
low-ohmic
voltage drop
75 mV
PMOS switch
low-ohmic
voltage drop
hub board
resistance
25 mV
3%, as shown in
voltage drop
resistance
hub board
(1)
25 mV
4.75 V(min)
4.75 V(min)
(1)
V BUS
D
D
GND
SHIELD
Figure
V BUS
D
D
GND
SHIELD
MGR781
USB stand-alone hub
MGR782
7.
© Philips Electronics N.V. 2000. All rights reserved.
downstream
connector
ISP1122
port
downstream
connector
port
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