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參數(shù)資料
| 型號： | LM3544 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Quad Port USB Power Distribution Switch and Over-Current Protection |
| 中文描述： | 四端口USB電源配電開關(guān)和過電流保護 |
| 文件頁數(shù)： | 10/13頁 |
| 文件大?。?/td> | 349K |
| 代理商： | LM3544 |
Application Information
(Continued)
tantalum capacitor is recommended. The input supply
should be further bypassed with a 0.01 μF - 0.1 μF ceramic
capacitor, placed close to the device. The ceramic capacitor
reduces ringing on the supply that can occur when a short is
present at the output of a port.
Extending the Fault Flag Delay
While the 7 ms (typical) internal delay in reporting flag
conditions is adequate for most applications, the delay can
be extended by connecting external RC filters to the FLAG
pins, as shown in Figure 5
Power Dissipation and Junction Temperature
A few simple calculations will allow a designer to calculate
the approximate operating temperature of the LM3544 for a
given application. The large currents possible through the
low resistance power MOSFET combined with the high
thermal resistance of the SOIC package, in relation to power
packages, make this estimate an important design step.
Begin the estimate by determining R
at the expected
operating temperature using the graphs in the Typical
Performance Characteristics section of this datasheet. Next,
calculate the power dissipation through the switch with
Equation (1)
PD = R
ON
*
I
DS2
Note:
Equation for power dissipation neglects portion that
comes from LM3544 quiescent current because this value
will almost always be insignificant.
Using this figure, determine the junction temperature with
Equation (2)
T
J
= PD
*
θ
JA
+ T
A
.
Where:
θ
= SOIC Thermal Resistance: 130C/W and T
A
=Ambient
Temperature (C).
Compare the calculated temperature with the expected
temperature used to estimate R
. If they do not reasonably
match, re-estimate R
using a more appropriate operating
temperature and repeat the calculations. Reiterate as
necessary.
(1)
(2)
PCB Layout Considerations
In order to meet the USB requirements for voltage drop,
droop and EMI, each component used in this circuit must be
evaluated for its contribution to the circuit performance.
These principles are illustrated in Figure 6 The following
PCB layout rules and guidelines are recommended
1.
Place the switch as close to the USB connector as
possible. Keep all V
bus
traces as short as possible and
use at least 50-mil, 1 ounce copper for all V
bus
traces.
Solder plating the traces will reduce the trace resistance.
2.
Avoid vias as much as possible. If vias are used, use
multiple vias in parallel and/or make them as large as
possible.
3.
Place the output capacitor and ferrite beads as close to
the USB connector as possible.
4.
If ferrite beads are used, use wires with minimum
resistance and large solder pads to minimize connection
resistance.
10120828
FIGURE 5. Typical Circuit for Lengthening the Internal
Flag Delay
10120827
FIGURE 6. Self-Powered Hub Connections and Per-Port Voltage Drop
L
www.national.com
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3544B-H E WAF | 制造商:Texas Instruments 功能描述: |
| LM3544M-H | 制造商:Texas Instruments 功能描述:2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO16 |
| LM3544M-H/NOPB | 功能描述:IC USB QUAD PORT SWITCH 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 電源分配開關(guān) 系列:- 特色產(chǎn)品:XRP252 Switches 標準包裝:1 系列:- 類型:高端開關(guān) 輸出數(shù):2 Rds（開）:140 毫歐 內(nèi)部開關(guān):是 電流限制:1.15A 輸入電壓:1.75 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-WFDFN 裸露焊盤 供應(yīng)商設(shè)備封裝:10-TDFN（3x3） 包裝:Digi-Reel® 其它名稱:1016-1691-6 |
| LM3544M-L | 功能描述:電源開關(guān) IC - USB RoHS:否 制造商:Micrel 電源電壓-最小:2.7 V 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:SOIC-8 封裝:Tube |
| LM3544M-L/NOPB | 功能描述:電源開關(guān) IC - USB RoHS:否 制造商:Micrel 電源電壓-最小:2.7 V 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:SOIC-8 封裝:Tube |
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