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參數(shù)資料
| 型號： | LM2670S-5.0 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SIMPLE SWITCHER High Efficiency 3A Step-Down Voltage Regulator with Sync |
| 中文描述： | 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PSSO7 |
| 封裝： | TO-263, 7 PIN |
| 文件頁數(shù)： | 11/23頁 |
| 文件大小： | 361K |
| 代理商： | LM2670S-5.0 |
Application Hints
(Continued)
SIMPLE DESIGN PROCEDURE
Using the nomographs and tables in this data sheet (or use
the available design software at http://www.national.com) a
complete step-down regulator can be designed in a few
simple steps.
Step 1:
Define the power supply operating conditions:
Required output voltage
Maximum DC input voltage
Maximum output load current
Step 2:
Set the output voltage by selecting a fixed output
LM2670 (3.3V, 5V or 12V applications) or determine the re-
quired feedback resistors for use with the adjustable
LM2670ADJ
Step 3:
Determine the inductor required by using one of the
four nomographs, Figure 3 through Figure 6 Table 1 pro-
vides a specific manufacturer and part number for the induc-
tor.
Step 4:
Using Table 3 (fixed output voltage) or Table 6 (ad-
justable output voltage), determine the output capacitance
required for stable operation. Table 2 provides the specific
capacitor type from the manufacturer of choice.
Step 5:
Determine an input capacitor from Table 4 for fixed
output voltage applications. Use Table 2 to find the specific
capacitor type. For adjustable output circuits select a capaci-
tor from Table 2 with a sufficient working voltage (WV) rating
greater than Vin max, and an rms current rating greater than
one-half the maximum load current (2 or more capacitors in
parallel may be required).
Step 6:
Select a diode from Table 5. The current rating of the
diode must be greater than I load max and the Reverse Volt-
age rating must be greater than Vin max.
Step 7:
Include a 0.01μF/50V capacitor for Cboost in the de-
sign.
FIXED OUTPUT VOLTAGE DESIGN EXAMPLE
A system logic power supply bus of 3.3V is to be generated
from a wall adapter which provides an unregulated DC volt-
age of 13V to 16V. The maximum load current is 2.5A.
Through-hole components are preferred.
Step 1:
Operating conditions are:
Vout = 3.3V
Vin max = 16V
Iload max = 2.5A
Step 2:
Select an LM2670T-3.3. The output voltage will have
a tolerance of
±
2% at room temperature and
±
3% over the full operating
temperature range.
Step 3:
Use the nomograph for the 3.3V device ,Figure 3
The intersection of the 16V horizontal line (V
max) and the
2.5A vertical line (I
load
max) indicates that L33, a 22μH in-
ductor, is required.
From Table 1, L33 in a through-hole component is available
from Renco with part number RL-1283-22-43 or part number
PE-53933 from Pulse Engineering.
Step 4:
Use Table 3 to determine an output capacitor. With a
3.3V output and a 22μH inductor there are four through-hole
output capacitor solutions with the number of same type ca-
pacitors 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:
1 x 220μF/10V Sanyo OS-CON (code C5)
1 x 1000μF/35V Sanyo MV-GX (code C10)
1 x 2200μF/10V Nichicon PL (code C5)
1 x 1000μF/35V Panasonic HFQ (code C7)
Step 5:
Use Table 4 to select an input capacitor. With 3.3V
output and 22μH there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
rms current rating greater than 1.25A (1/2 I
max). Again
using Table 2 for specific component characteristics the fol-
lowing choices are suitable:
1 x 1000μF/63V Sanyo MV-GX (code C14)
1 x 820μF/63V Nichicon PL (code C24)
1 x 560μF/50V Panasonic HFQ (code C13)
Step 6:
From Table 5 a 3A Schottky diode must be selected.
For through-hole components 20V rated diodes are sufficient
and 2 part types are suitable:
1N5820
SR302
Step 7:
A 0.01μF 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 re-
quired is 2A 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 = 2A
Step 2:
Select an LM2670S-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 0.15
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.
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2670SADJ | 制造商:Texas Instruments 功能描述: |
| LM2670S-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 安裝風格:SMD/SMT |
| LM2670S-ADJ | 制造商:Texas Instruments 功能描述:IC, SWITCHING REG 3A ADJ, SMD, 2670 制造商:Texas Instruments 功能描述:IC, SWITCHING REG 3A ADJ, SMD, 2670; Primary Input Voltage:40V; No. of Outputs:1; Output Voltage:37V; Output Current:3A; Voltage Regulator Case Style:TO-263; No. of Pins:7; Operating Temperature Min:-40C; Operating Temperature ;RoHS Compliant: Yes |
| LM2670S-ADJ/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 HIGH EFF 3A 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 |
| LM2670S-ADJ/NOPB | 制造商:Texas Instruments 功能描述:IC, DC/DC CONVERTER, 3A |
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