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參數(shù)資料
| 型號： | LM11171 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 800mA Low-Dropout Linear Regulator(800mA低壓差線性穩(wěn)壓器) |
| 中文描述： | 800mA的低壓差線性穩(wěn)壓器（800mA的低壓差線性穩(wěn)壓器） |
| 文件頁數(shù)： | 10/19頁 |
| 文件大?。?/td> | 408K |
| 代理商： | LM11171 |
APPLICATION NOTE
(Continued)
into the output of the regulator. The discharge current de-
pends on the value of the capacitor, the output voltage of the
regulator, and rate of decrease of V
. In the LM1117 regu-
lators, the internal diode between the output and input pins
can withstand microsecond surge currents of 10A to 20A.
With an extremely large output capacitor (
≥
1000 μF), and
with input instantaneously shorted to ground, the regulator
could be damaged.
In this case, an external diode is recommended between the
output and input pins to protect the regulator, as shown in
Figure 4
5.0 Heatsink Requirements
When an integrated circuit operates with an appreciable
current, its junction temperature is elevated. It is important to
quantify its thermal limits in order to achieve acceptable
performance and reliability. This limit is determined by sum-
ming the individual parts consisting of a series of tempera-
ture rises from the semiconductor junction to the operating
environment. A one-dimensional steady-state model of con-
duction heat transfer is demonstrated in Figure 5 The heat
generated at the device junction flows through the die to the
die attach pad, through the lead frame to the surrounding
case material, to the printed circuit board, and eventually to
the ambient environment. Below is a list of variables that
may affect the thermal resistance and in turn the need for a
heatsink.
R
θ
JC
(Component Vari-
ables)
Leadframe Size &
Material
No. of Conduction Pins
R
θ
CA
(Application Vari-
ables)
Mounting Pad Size,
Material, & Location
Placement of Mounting
Pad
PCB Size & Material
Traces Length & Width
Adjacent Heat Sources
Die Size
Die Attach Material
Molding Compound Size
and Material
Volume of Air
Ambient Temperatue
Shape of Mounting Pad
The LM1117 regulators have internal thermal shutdown to
protect the device from over-heating. Under all possible
operating conditions, the junction temperature of the LM1117
must be within the range of 0C to 125C. A heatsink may be
required depending on the maximum power dissipation and
maximum ambient temperature of the application. To deter-
mine if a heatsink is needed, the power dissipated by the
regulator, P
D
, must be calculated:
I
IN
= I
L
+ I
G
P
D
= (V
IN
-V
OUT
)I
L
+ V
IN
I
G
Figure 6 shows the voltages and currents which are present
in the circuit.
DS100919-15
FIGURE 4. Regulator with Protection Diode
DS100919-37
FIGURE 5. Cross-sectional view of Integrated Circuit
Mounted on a printed circuit board. Note that the case
temperature is measured at the point where the leads
contact with the mounting pad surface
DS100919-16
FIGURE 6. Power Dissipation Diagram
L
www.national.com
10
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| LM1117-1.5 | 制造商:CYSTEKEC 制造商全稱:Cystech Electonics Corp. 功能描述:1A Low Dropout Positive Voltage Regulator |
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| LM1117-2.5 | 制造商:CYSTEKEC 制造商全稱:Cystech Electonics Corp. 功能描述:1A Low Dropout Positive Voltage Regulator |
| LM1117-2.85 | 制造商:CYSTEKEC 制造商全稱:Cystech Electonics Corp. 功能描述:1A Low Dropout Positive Voltage Regulator |
| LM1117-2.85-220 | 制造商:FCI 制造商全稱:First Components International 功能描述:800mA Low-dropout Linear Regulator Temperature Range Output Current 800mA |
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