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參數(shù)資料
| 型號(hào)： | LM2679T-3.3 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 392 Series Industrial Potentiometer, Conductive Plastic Element, PC Terminals, 0.5 W Power Rating, 2.5 kOhm Resistance Value |
| 中文描述： | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, ZFM7 |
| 封裝： | TO-220, 7 PIN |
| 文件頁數(shù)： | 13/24頁 |
| 文件大?。?/td> | 355K |
| 代理商： | LM2679T-3.3 |
Application Hints
(Continued)
Step 2:
Select an LM2679S-ADJ. To set the output voltage
to 14.9V two resistors need to be chosen (R1 and R2 in Fig-
ure 2). For the adjustable device the output voltage is set by
the following relationship:
Where V
FB
is the feedback voltage of typically 1.21V.
A recommended value to use for R1 is 1K. In this example
then R2 is determined to be:
R2 = 11.23K
The closest standard 1% tolerance value to use is 11.3K
This will set the nominal output voltage to 14.88V which is
within 0.5% of the target value.
Step 3:
To use the nomograph for the adjustable device, Fig-
ure
6
requires
a
calculation
Volt
microsecond constant (E
T expressed in V
μS) from
the following formula:
of
the
inductor
where V
is the voltage drop across the internal power
switch which is R
ds(ON)
times I
load
. In this example this would
be typically 0.12
is the voltage drop
across the forward bisased Schottky diode, typically 0.5V.
The switching frequency of 260KHz is the nominal value to
use to estimate the ON time of the switch during which en-
ergy is stored in the inductor.
For this example E
T is found to be:
Using Figure 6 the intersection of 27V
μS horizontally and
the 3.5A vertical line (I
max) indicates that L48 , a 47μH
inductor, or L49, a 33μH inductor could be used. Either in-
ductor will be suitable, but for this example selecting the
larger inductance will result in lower ripple current.
From Table 1, L48 in a surface mount component is available
from Pulse Engineering with part number P0848.
Step 4:
Use Table 6 to determine an output capacitor. With a
14.8V output the 12.5 to 15V row is used and with a 47μH in-
ductor there are three surface mount output capacitor solu-
tions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
1 x 33μF/20V AVX TPS (code C6)
1 x 47μF/20V Sprague 594 (code C8)
1 x 47μF/20V Kemet T495 (code C8)
Important Note:
When using the adjustable device in low
voltage applications (less than 3V output), if the nomograph,
Figure 6, selects an inductance of 22μH or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable op-
eration becomes impractical. It is recommended to use ei-
ther a 33μH or 47μH inductor and the output capacitors from
Table 6.
Step 5:
An input capacitor for this example will require at
least a 35V WV rating with an rms current rating of 1.75A
(1/2 Iout max). From Table 2 it can be seen that C12, a
33μF/35V
capacitor
from
voltage/current rating of the surface mount components and
that two of these capacitor in parallel will be adquate.
Step 6:
From Table 5 a 5A or more Schottky diode must be
selected. For surface mount diodes with a margin of safety
on the voltage rating one of two diodes can be used:
MBRD1545CT
6TQ045S
Step 7:
A 0.01μF capacitor will be used for Cboost.
The softstart pin will be left open circuited.
Step 8:
Determine a value for R
to provide a peak switch
current limit of at least 3.5A plus 50% or 5.25A.
Sprague,
has
the
highest
Use a value of 7.15K
.
L
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2679T-5.0 | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2679T-5.0/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2679TADJ | 制造商:NATIONAL 功能描述:New |
| LM2679T-ADJ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2679T-ADJ | 制造商:Texas Instruments 功能描述:SWITCHING REG 5A ADJ 2679 TO2207 |
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