- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄364699 > APPNOTE17 Universal Serial Bus Power Management PDF資料下載
參數(shù)資料
| 型號： | APPNOTE17 |
| 英文描述： | Universal Serial Bus Power Management |
| 中文描述： | 通用串行總線電源管理 |
| 文件頁數(shù)： | 4/12頁 |
| 文件大?。?/td> | 125K |
| 代理商： | APPNOTE17 |
Application Note 17
Micrel
Application Note 17
4
October 1998
Component Selection
Due to the limited voltage drop budget allowed for self-
powered hubs, each component must be evaluated for its
contribution to voltage drop.
Polyfuse Protection Limitations
Most resettable Polymer Positive Temperature Coefficient
Fuses (PPTC—polyfuse) are not suitable as the sole over-
current protection in USB self-powered hubs. A self-resetting
2.5A PPTC may take up to 100 seconds to trip at 5A. The
voltage drop due to the higher on-resistance of lower current-
rated polyfuses placed on individual ports may exceed the
100mV self-powered hub drop budget.
Polyfuse Resistance Increases
Polyfuses may permanently increase resistance after a trip
event or exposure to high temperature, such as wave-
soldering. A typical 0.11A polyfuse specified to pass 0.67A at
70
°
C, requires 5 seconds to trip with a 5A load. Its pretripped
on-resistance ranges from 50m
to 100m
at 25
°
C ambient,
rising permanently to approximately 170m
after an initial
trip. This exceeds the 140m
resistance recommended by
USB. Polyfuses require additional components to be switched
off or reliably report overcurrent.
Power Regulators
Linear regulators may be used to provide cost-effective
closely-regulated standard voltages from unregulated power
supplies. Low-dropout (LDO) regulators provide current-
limited,
±
2% regulated output over a wide range of input
voltage and output loads. LDO regulators have a logic enable
pin and an error flag output that indicates current limiting or
undervoltage.
5V LDO regulators can provide regulated voltage output with
as little as 5.35V input under full load. Micrel’s MIC29301
LDO regulator is rated for continuous 3A output with a typical
3.8A current limit and short-circuit limit of less than 5A.
MIC29301 has a logic-level, noninverting, output-enable pin
that allows the output to be turned on or off, and an open-drain
error flag that conducts to ground if the device is in current
limit or undervoltage lockout (low input—excessive dropout).
Figure 5 shows a stand-alone self-powered hub using an
MIC29301-5.0.
Integrated High-Side Power Switches
For hubs with a regulated power supply, integrated power
switches provide an economical, robust power management
solution. Micrel’s MIC2505/25 single and MIC2506/26 dual
switches react quickly to overloads, providing safety margin
and overall power control and have an error flag output. The
enable feature is available as inverting or noninverting logic,
allowing flexibility in choice of hub controllers. All integrated
switches are guaranteed to survive an output short circuit with
a 5.25V input. Table 3 shows the characteristics of Micrel’s
USB power switches.
Part Number Switches
Logic
I
OUT
2.0A
R
ON
35m
35m
70m
140m
140m
140m
140m
MIC2505-1
single
noninverting
MIC2505-2
single
inverting
2.0A
MIC2506
single
noninverting
1.0A
MIC2525-1
single
noninverting
0.5A
MIC2525-2
single
inverting
0.5A
MIC2526-1
dual
noninverting
0.5A
MIC2526-2
dual
inverting
0.5A
Table 3. Micrel Switches
56mV
Cable
Connector
V
BUS
GND
Maximum
Cable
Resistance
0.190
15mV
0.03
15mV
0.03
0.190
Cable
Connector
15mV
0.03
15mV
0.03
95mV
95mV
4.7μF
to
10μF
0.1μF
0.015
6mV
6mV
(trace resistance)
0.015
400mA max.
0.14
120μF
1.5mV
0.015
1.5mV
0.015
V
BUS
GND
4.40V min.
100mA max.
1mV
0.010
Ferrite Bead
(solder joint resistance)
0.010
1mV
0.01μF
USB Cable Assembly
USB Bus-Powered Hub
1/2
MIC2526
Switch
Cable
Connector
From Upstream
USB Port
4.75V min.
500mA max.
2 of 4 Downstream
Peripheral Ports
V
BUS
GND
1.5mV
0.015
1.5mV
0.015
4.40V min.
100mA max.
1mV
0.010
0.010
1mV
0.01μF
Additional Ports
100mV(max)
350mV(max)
The upstream USB port
can supply 500mA max.
Up to 100mA is allocated
to a processor in the
bus-powered hub.
Figure 4. Bus-Powered Hub Voltage-Drop Analysis
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| APPNOTE32 | Dual Current-Limiting Switch for USB Applications |
| APPNOTE36 | Electroluminescent Display Drivers |
| APRX178L | PHOTOLINK Optical TX/RX Modules |
| APRX178LT | PHOTOLINK Optical TX/RX Modules |
| APSC56-21 | SURFACE MOUNT DISPLAY |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| APPNOTE32 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Dual Current-Limiting Switch for USB Applications |
| APPNOTE36 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Electroluminescent Display Drivers |
| APPNOTESMP9100 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Understanding the Power Rating of Caddock MP9100 Resistors |
| APP-NPA1006-CT | 制造商:Nitronex 功能描述:RF & MW AMPLIFIER EVALUATION BOARD/DESIGNER KIT |
| APP-NPT25015-UNTUNED | 制造商:Nitronex 功能描述:RF TRANSISTOR EVALUATION BOARD |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。