參數(shù)資料
型號： LM2678LD-5.0
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： 8.75 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14
封裝： LLP-14
文件頁數(shù)： 5/26頁
文件大?。?/td> 441K
代理商： LM2678LD-5.0
Application Hints (Continued)
Step 3: Use the nomograph for the 3.3V device ,Figure 3.
The intersection of the 16V horizontal line (V
in max) and the
4A vertical line (I
load max) indicates that L46, a 15H induc-
tor, is required.
From Table 1, L46 in a through-hole component is available
from Renco with part number RL-1283-15-43.
Step 4: Use Table 3 to determine an output capacitor. With a
3.3V output and a 15H inductor there are four through-hole
output capacitor solutions with the number of same type
capacitors to be paralleled and an identifying capacitor code
given. Table 2 provides the actual capacitor characteristics.
Any of the following choices will work in the circuit:
2 x 220F/10V Sanyo OS-CON (code C5)
2 x 820F/16V Sanyo MV-GX (code C5)
1 x 3900F/10V Nichicon PL (code C7)
2 x 560F/35V Panasonic HFQ (code C5)
Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 15H there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
rms current rating greater than 2A (1/2 I
load max). Again
using Table 2 for specific component characteristics the
following choices are suitable:
2 x 680F/63V Sanyo MV-GX (code C13)
1 x 1200F/63V Nichicon PL (code C25)
1 x 1500F/63V Panasonic HFQ (code C16)
Step 6: From Table5a5A or more Schottky diode must be
selected. For through-hole components only 40V rated di-
odes are indicated and 4 part types are suitable:
1N5825
MBR745
80SQ045
6TQ045
Step 7: A 0.01F capacitor will be used for Cboost.
ADJUSTABLE OUTPUT DESIGN EXAMPLE
In this example it is desired to convert the voltage from a two
battery automotive power supply (voltage range of 20V to
28V, typical in large truck applications) to the 14.8VDC alter-
nator supply typically used to power electronic equipment
from single battery 12V vehicle systems. The load current
required is 3.5A maximum. It is also desired to implement the
power supply with all surface mount components.
Step 1: Operating conditions are:
Vout = 14.8V
Vin max = 28V
Iload max = 3.5A
Step 2: Select an LM2678S-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,
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.
LM2678
www.national.com
13
相關(guān)PDF資料
PDF描述
LM2678LDX-12 8.75 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, DSO14
LM2734XMKX/NOPB 2.5 A SWITCHING REGULATOR, 1900 kHz SWITCHING FREQ-MAX, PDSO6
LM3102TLX-1 SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PBGA28
LM3102TL-1 SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PBGA28
LM3411A-3.3MWC 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 3.3 V, UUC
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2678S-12 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
LM2678S-12/NOPB 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 HIGH EFF 5A STEP- DOWN VLTG REG 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
LM2678S3.3 制造商:National Semiconductor 功能描述:Conv DC-DC Single Step Down 8V to 40V 8-Pin(7+Tab) TO-263 Rail
LM2678S-3.3 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
LM2678S-3.3/NOPB 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 HIGH EFF 5A STEP- DOWN VLTG REG 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
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。

采購需求

(若只采購一條型號，填寫一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購。也可以進(jìn)入我的后臺，查看報價

發(fā)布成功！您可以繼續(xù)發(fā)布采購。也可以進(jìn)入我的后臺，查看報價

*型號 *數(shù)量 廠商 批號 封裝
添加更多采購

我的聯(lián)系方式

*
*
*