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参数资料
| 型号： | LM2673LDX-12 |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封装： | LLP-14 |
| 文件页数： | 4/25页 |
| 文件大小： | 433K |
| 代理商： | LM2673LDX-12 |
Application Hints (Continued)
If this feature is not desired, leave the Softstart pin (pin 7)
open circuited
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
LM2673 (3.3V, 5V or 12V applications) or determine the
required feedback resistors for use with the adjustable
LM2673ADJ
Step 3: Determine the inductor required by using one of the
vides a specific manufacturer and part number for the induc-
tor.
Step 4: Using Table 3 (fixed output voltage) or Table 6
(adjustable output voltage), determine the output capaci-
tance 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
Voltage rating must be greater than Vin max.
Step 7: Include a 0.01F/50V capacitor for Cboost in the
design and then determine the value of a softstart capacitor
if desired.
Step 8: Define a value for R
ADJ to set the peak switch
current limit to be at least 20% greater than Iout max to allow
for at least 30% inductor ripple current (±15% of Iout). For
designs that must operate over the full temperature range
the switch current limit should be set to at least 50% greater
than Iout max (1.5 x I
out max).
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. A
softstart delay time of 50mS is desired. Through-hole com-
ponents are preferred.
Step 1: Operating conditions are:
Vout = 3.3V
Vin max = 16V
Iload max = 2.5A
Step 2: Select an LM2673T-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
in max) and the
2.5A vertical line (I
load max) indicates that L33, a 22H
inductor, 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 33H 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:
1 x 220F/10V Sanyo OS-CON (code C5)
1 x 1000F/35V Sanyo MV-GX (code C10)
1 x 2200F/10V Nichicon PL (code C5)
1 x 1000F/35V Panasonic HFQ (code C7)
Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 22H 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
load max). Again
using Table 2 for specific component characteristics the
following choices are suitable:
1 x 1000F/63V Sanyo MV-GX (code C14)
1 x 820F/63V Nichicon PL (code C24)
1 x 560F/50V Panasonic HFQ (code C13)
Step 6: From Table5a3A or more Schottky diode must be
selected. The 20V rated diodes are sufficient for the appli-
cation and for through-hole components two part types are
suitable:
1N5820
SR302
Step 7: A 0.01F capacitor will be used for Cboost. For the
50mS softstart delay the following parameters are to be
used:
I
SST: 3.7A
t
SS: 50mS
V
SST: 0.63V
V
OUT: 3.3V
V
SCHOTTKY: 0.5V
V
IN: 16V
Using Vin max ensures that the softstart delay time will be at
least the desired 50mS.
Using the formula for Css a value of 0.148F is determined
to be required. Use of a standard value 0.22F capacitor will
produce more than sufficient softstart delay.
Step 8: Determine a value for R
ADJ to provide a peak switch
current limit of at least 2.5A plus 50% or 3.75A.
Use a value of 10K
.
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 2A 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
LM2673
www.national.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2673S-12 | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2673S12 | 制造商:Texas Instruments 功能描述:IC SWITCHING REG 3A 12V SMD 2673 |
| LM2673S-12/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2673S-3.3 | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2673S-3.3/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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