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參數資料
| 型號： | ISP1123 |
| 廠商： | NXP Semiconductors N.V. |
| 英文描述： | Universal Serial Bus compound hub |
| 中文描述： | 通用串行總線復合樞紐 |
| 文件頁數： | 25/49頁 |
| 文件大?。?/td> | 1155K |
| 代理商： | ISP1123 |
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Philips Semiconductors
ISP1123
USB compound hub
Preliminary specification
Rev. 01 — 5 October 1999
25 of 49
9397 750 06325
Philips Electronics N.V. 1999. All rights reserved.
13. Overcurrent detection
The ISP1123 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).
13.1 Overcurrent circuit description
The integrated overcurrent detection circuit of ISP1123 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.
13.2 Power switch selection
From the voltage drop analysis given in
Figure 7
,
Figure 8
and
Figure 9
, 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.
The ISP1123 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
1
.
13.3 Tuning the overcurrent trip voltage
The ISP1123 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 10
). R
tu
tunes up the trip voltage
V
trip
and R
td
tunes it down
according to
Equation 1
.
(1)
with I
ref(nom)
= 5
μ
A and I
OC(nom)
= 0.5
μ
A.
1.
The following PMOS power switches have been tested to work well with the ISP1123: Philips PHP109, Vishay Siliconix Si2301DS,
Fairchild FDN338P.
V
trip
V
trip intrinsic
)
I
ref
R
tu
I
OC
R
td
–
+
=
相關PDF資料 |
PDF描述 |
|---|---|
| ISP1123D | Universal Serial Bus compound hub |
| ISP1123NB | Universal Serial Bus compound hub |
| ISP1130 | Universal Serial Bus compound hub with integrated keyboard controller |
| ISP1130DL | Universal Serial Bus compound hub with integrated keyboard controller |
| ISP1130N | Universal Serial Bus compound hub with integrated keyboard controller |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ISP1123BD | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus compound hub |
| ISP1123D | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus compound hub |
| ISP1123NB | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus compound hub |
| ISP1130 | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus compound hub with integrated keyboard controller |
| ISP1130DL | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Universal Serial Bus compound hub with integrated keyboard controller |
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