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參數資料
| 型號： | ISP1122A |
| 廠商： | NXP Semiconductors N.V. |
| 英文描述： | Universal Serial Bus stand-alone hub |
| 中文描述： | 通用串行總線獨立的樞紐 |
| 文件頁數： | 24/48頁 |
| 文件大小： | 1150K |
| 代理商： | ISP1122A |
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Philips Semiconductors
ISP1122A
USB stand-alone hub
Preliminary specification
Rev. 01 — 27 March 2000
24 of 48
9397 750 06986
Philips Electronics N.V. 2000. All rights reserved.
The PCB resistance may cause a drop of 25 mV, which leaves 75 mV for the power
switch and overcurrent sense device. The voltage drop components are shown in
Figure 8
.
For bus-powered hubs overcurrent protection is optional. It may be implemented for
all downstream ports on a global or individual basis.
12. Overcurrent detection
The ISP1122A has an analog overcurrent detection circuit for monitoring downstream
port lines. This circuit automatically reports an overcurrent condition to the host and
turns off the power to the faulty port. The host must reset the condition flag.
Pins OC1 to OC5/GOC are used for individual port overcurrent detection. Pin
OC5/GOC can also be used for global overcurrent detection. This is controlled by
input INDV (see
Table 4
).
The overcurrent detection circuit can be switched off using an external EEPROM (see
Table 23
). In this case, the overcurrent pins OCn function as logic inputs (TTL level).
12.1 Overcurrent circuit description
The integrated overcurrent detection circuit of ISP1122A senses the voltage drop
across the power switch or an extra low-ohmic sense resistor. When the port draws
too much current, the voltage drop across the power switch exceeds the trip voltage
threshold (
V
trip
). The overcurrent circuit detects this and switches off the power
switch control signal after a delay of 15 ms (t
trip
). This delay acts as a ‘debounce’
period to minimize false tripping, especially during the inrush current produced by ‘hot
plugging’ of a USB device.
12.2 Power switch selection
From the voltage drop analysis given in
Figure 6
,
Figure 7
and
Figure 8
, the power
switch has a voltage drop budget of 75 mV. For individual self-powered mode, the
current drawn per port can be up to 500 mA. Thus the power switch should have
maximum on-resistance of 150 m
.
If the voltage drop due to the hub board resistance can be minimized, the power
switch can have more voltage drop budget and therefore a higher on-resistance.
Power switches with a typical on-resistance of around 100 m
fit into this application.
(1) Includes PCB traces, ferrite beads, etc.
Fig 8.
Typical voltage drop components in bus-powered mode (no overcurrent detection).
handbook, full pagewidth
MGR783
low-ohmic
PMOS switch
ISP1122
power
switch
VBUS
D
+
D
GND
SHIELD
VBUS
D
+
D
GND
SHIELD
4.40 V(min)
4.50 V(min)
downstream
port
connector
upstream
port
connector
hub board
resistance
voltage drop
25 mV
voltage drop
75 mV
(1)
相關PDF資料 |
PDF描述 |
|---|---|
| ISP1122ABD | Universal Serial Bus stand-alone hub |
| ISP1122AD | Universal Serial Bus stand-alone hub |
| ISP1122ANB | Universal Serial Bus stand-alone hub |
| ISP1122 | Universal Serial Bus stand-alone hub |
| ISP1122BD | Universal Serial Bus stand-alone hub |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ISP1122ABD | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus stand-alone hub |
| ISP1122AD | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus stand-alone hub |
| ISP1122ANB | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus stand-alone hub |
| ISP1122BD | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus stand-alone hub |
| ISP1122D | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus stand-alone hub |
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