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參數(shù)資料
| 型號： | LM2679S-3.3 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit |
| 中文描述： | 8.1 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PSSO7 |
| 封裝： | TO-263, 7 PIN |
| 文件頁數(shù)： | 10/24頁 |
| 文件大小： | 355K |
| 代理商： | LM2679S-3.3 |
Application Hints
(Continued)
Power supply design using the LM2679 is greatly simplified
by using recommended external components. A wide range
of inductors, capacitors and Schottky diodes from several
manufacturers have been evaluated for use in designs that
cover the full range of capabilities (input voltage, output volt-
age and load current) of the LM2679. A simple design proce-
dure using nomographs and component tables provided in
this data sheet leads to a working design with very little ef-
fort. Alternatively, the design software,
LM267X Made
Simple
(version 2.0), can also be used to provide instant
component selection, circuit performance calculations for
evaluation, a bill of materials component list and a circuit
schematic.
The individual components from the various manufacturers
called out for use are still just a small sample of the vast ar-
ray of components available in the industry. While these
components are recommended, they are not exclusively the
only components for use in a design. After a close compari-
son of component specifications, equivalent devices from
other manufacturers could be substituted for use in an appli-
cation.
Important considerations for each external component and
an explanation of how the nomographs and selection tables
were developed follows.
INDUCTOR
The inductor is the key component in a switching regulator.
For efficiency the inductor stores energy during the switch
ON time and then transfers energy to the load while the
switch is OFF.
Nomographs are used to select the inductance value re-
quired for a given set of operating conditions. The nomo-
graphs assume that the circuit is operating in continuous
mode (the current flowing through the inductor never falls to
zero). The magnitude of inductance is selected to maintain a
maximum ripple current of 30% of the maximum load cur-
rent. If the ripple current exceeds this 30% limit the next
larger value is selected.
The inductors offered have been specifically manufactured
to provide proper operation under all operating conditions of
input and output voltage and load current. Several part types
are offered for a given amount of inductance. Both surface
mount and through-hole devices are available. The inductors
from each of the three manufacturers have unique charac-
teristics.
Renco: ferrite stick core inductors; benefits are typically low-
est cost and can withstand ripple and transient peak currents
above the rated value. These inductors have an external
magnetic field, which may generate EMI.
Pulse Engineering: powdered iron toroid core inductors;
these also can withstand higher than rated currents and, be-
ing toroid inductors, will have low EMI.
Coilcraft: ferrite drum core inductors; these are the smallest
physical size inductors and are available only as surface
mount components. These inductors also generate EMI but
less than stick inductors.
OUTPUT CAPACITOR
The output capacitor acts to smooth the dc output voltage
and also provides energy storage. Selection of an output ca-
pacitor, with an associated equivalent series resistance
(ESR), impacts both the amount of output ripple voltage and
stability of the control loop.
The output ripple voltage of the power supply is the product
of the capacitor ESR and the inductor ripple current. The ca-
pacitor types recommended in the tables were selected for
having low ESR ratings.
In addition, both surface mount tantalum capacitors and
through-hole aluminum electrolytic capacitors are offered as
solutions.
Impacting frequency stability of the overall control loop, the
output capacitance, in conjunction with the inductor, creates
a double pole inside the feedback loop. In addition the ca-
pacitance and the ESR value create a zero. These fre-
quency response effects together with the internal frequency
compensation circuitry of the LM2679 modify the gain and
phase shift of the closed loop system.
As a general rule for stable switching regulator circuits it is
desired to have the unity gain bandwidth of the circuit to be
limited to no more than one-sixth of the controller switching
frequency. With the fixed 260KHz switching frequency of the
LM2679, the output capacitor is selected to provide a unity
gain bandwidth of 40KHz maximum. Each recommended ca-
pacitor value has been chosen to achieve this result.
DS100847-24
FIGURE 2. Basic circuit for adjustable output voltage applications
L
www.national.com
10
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM2679S-5.0 | SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit |
| LM2679T-12 | 392 Series Industrial Potentiometer, Conductive Plastic Element, PC Terminals, 0.5 W Power Rating, 250 Ohm Resistance Value |
| LM2679T-3.3 | 392 Series Industrial Potentiometer, Conductive Plastic Element, PC Terminals, 0.5 W Power Rating, 2.5 kOhm Resistance Value |
| LM2679T-5.0 | SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit |
| LM2679T-ADJ | 392 Series Industrial Potentiometer, Conductive Plastic Element, PC Terminals, 0.5 W Power Rating, 500 Ohm Resistance Value |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2679S-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 安裝風格:SMD/SMT |
| LM2679S-5.0/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 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 安裝風格:SMD/SMT |
| LM2679S5.0NOPB | 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 |
| LM2679S50 | 制造商:Texas Instruments 功能描述:SWITCHING REG 5A 5.0V SMD 2679 |
| LM2679SADJ | 制造商:Texas Instruments 功能描述: |
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