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參數資料
| 型號： | LM2679LD-ADJ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14 |
| 封裝： | LLP-14 |
| 文件頁數： | 5/25頁 |
| 文件大?。?/td> | 438K |
| 代理商： | LM2679LD-ADJ |
Application Hints (Continued)
required is 3.5A maximum. It is also desired to implement the
power supply with all surface mount components. Softstart is
not required.
Step 1: Operating conditions are:
Vout = 14.8V
Vin max = 28V
Iload max = 3.5A
Step 2: Select an LM2679S-ADJ. To set the output voltage
to 14.9V two resistors need to be chosen (R1 and R2 in
Figure 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,
6,
requires
a
calculation
of
the
inductor
Volt
microsecond constant (ET expressed in VS) from
the following formula:
where V
SAT is the voltage drop across the internal power
switch which is R
ds(ON) times Iload. In this example this would
be typically 0.12
x 3.5A or 0.42V and V
D 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
energy is stored in the inductor.
For this example E
T is found to be:
Using Figure 6, the intersection of 27V
S horizontally and
the 3.5A vertical line (I
load max) indicates that L48 , a 47H
inductor, or L49, a 33H inductor could be used. Either
inductor 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 47H
inductor there are three surface mount output capacitor so-
lutions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
1 x 33F/20V AVX TPS (code C6)
1 x 47F/20V Sprague 594 (code C8)
1 x 47F/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 22H or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable
operation becomes impractical. It is recommended to use
either a 33H or 47H 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
33F/35V
capacitor
from
Sprague,
has
the
highest
voltage/current rating of the surface mount components and
that two of these capacitor in parallel will be adquate.
Step 6: From Table5a5A 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 0.01F capacitor will be used for Cboost.
The softstart pin will be left open circuited.
Step 8: Determine a value for R
ADJ to provide a peak switch
current limit of at least 3.5A plus 50% or 5.25A.
Use a value of 7.15K
.
LLP Package Devices
The LM2679 is offered in the 14 lead LLP surface mount
package to allow for a significantly decreased footprint with
equivalent power dissipation compared to the TO-263. For
details on mounting and soldering specifications, refer to
Application Note AN-1187.
LM2679
www.national.com
13
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| LM2679LDX-12 | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14 |
| LM2679LDX-5.0 | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14 |
| LM2679SDX-5.0/NOPB | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14 |
| LM2679SD-12/NOPB | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14 |
相關代理商/技術參數 |
參數描述 |
|---|---|
| LM2679S-12 | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM2679S-12/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM2679S-3.3 | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM2679S-3.3/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM2679S-5.0 | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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