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參數(shù)資料
| 型號(hào)： | LM2623MMX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | General Purpose, Gated Oscillator Based, DC/DC Boost Converter |
| 中文描述： | 1.2 A SWITCHING REGULATOR, 2000 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | MINI, SO-8 |
| 文件頁(yè)數(shù)： | 9/11頁(yè) |
| 文件大小： | 216K |
| 代理商： | LM2623MMX |
Design Procedure
NON-LINEAR EFFECT
The LM2623 is very similar to the LM2621. The LM2623 is
based on the LM2621, except for the fact that the LM2623
takes advantage of a non-linear effect that allows for the duty
cycle to be programmable. The C3 capacitor is used to dump
charge on the FREQ pin in order to manipulate the duty
cycle of the internal oscillator. The part is being tricked to
behave in a certain manner, in the effort to make this Pulse
Frequency Modulated (PFM) boost switching regulator be-
have as a Pulse Width Modulated (PWM) boost switching
regulator.
CHOOSING THE CORRECT C3 CAPACITOR
The C3 capacitor allows for the duty cycle of the internal
oscillator to be programmable. Choosing the correct C3
capacitor to get the appropriate duty cycle for a particular
application circuit is a trial and error process. The non-linear
effect that C3 produces is dependent on the input voltage
and output voltage values. The correct C3 capacitor for
particular input and output voltage values cannot be calcu-
lated. Choosing the correct C3 capacitance is best done by
trial and error, in conjunction with the checking of the induc-
tor peak current to make sure your not too close to the
current limit of the device. As the C3 capacitor value in-
creases, so does the duty cycle. And conversely as the C3
capacitor value decreases, the duty cycle decreases. An
incorrect choice of the C3 capacitor can result in the part
prematurely tripping the current limit and/or double pulsing,
which could lead to the output voltage not being stable.
SETTING THE OUTPUT VOLTAGE
The output voltage of the step-up regulator can be set by
connecting a feedback resistive divider made of R
F1
and
R
F2
. The resistor values are selected as follows:
R
F2
= R
F1
/[(V
OUT
/ 1.24) 1]
A value of 50k to 100k is suggested for Rf2. Then, Rf1 can
be selected using the above equation.
V
DD
SUPPLY
AVdd supply of 3 to 5 volts is recommended for the LM2623.
This voltage can be bootstrapped from a much lower input
voltage by simply connecting the V
pin to V
. In the
event that the V
DD
supply voltage is not a low ripple voltage
source (less than 200 millivolts), it may be advisable to use
an RC filter to clean it up. Excessive ripple on V
DD
may
reduce the efficiency.
SETTING THE SWITCHING FREQUENCY
The switching frequency of the oscillator is selected by
choosing an external resistor (R3) connected between V
IN
and the FREQ pin. See the graph titled "Frequency vs V
“ in
the Typical Performance Characteristics section of the data
sheet for choosing the R3 value to achieve the desired
switching frequency. A high switching frequency allows the
use of very small surface mount inductors and capacitors
and results in a very small solution size. A switching fre-
quency between 300kHz and 2MHz is recommended.
OUTPUT DIODE SELECTION
A Schottky diode should be used for the output diode. The
forward current rating of the diode should be higher than the
peak input current, and the reverse voltage rating must be
higher than the output voltage. Do not use ordinary rectifier
diodes, since slow switching speeds and long recovery times
cause the efficiency and the load regulation to suffer.
Table 1
shows a list of the diode manufacturers.
LLP PACKAGE DEVICES
The LM2623 is offered in the 14 lead LLP surface mount
package to allow for increased power dissipation compared
to the MSOP-8. For details of the thermal performance as
well as mounting and soldering specifications, refer to
Ap-
plication Note AN-1187
.
TABLE 1. Suggested Manufacturers List
Inductors
Capacitors
Diodes
Coilcraft
Tel: (800) 322-2645
Fax: (708) 639-1469
Coiltronics
Tel: (407) 241-7876
Fax: (407) 241-9339
Pulse Engineering
Tel: (619) 674-8100
Fax: (619) 674-8262
Sprague/ Vishay
Tel: (207) 324-4140
Fax: (207) 324-7223
Kemet
Tel: (864) 963-6300
Fax: (864) 963-6521
Nichicon
Tel: (847) 843-7500
Fax: (847) 843-2798
Motorola
Tel: (800) 521-6274
Fax: (602) 244-6609
International Rectifier (IR)
Tel: (310) 322-3331
Fax: (310) 322-3332
General Semiconductor
Tel: (516) 847-3222
Fax: (516) 847-3150
L
www.national.com
9
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| LM2623MMX/NOPB | 功能描述:DC/DC 開(kāi)關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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| LM2630 | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:Synchronous Step-Down Power Supply Controller |
| LM2630B-ADJ WAF | 制造商:Texas Instruments 功能描述: |
| LM2630MTCADJ | 制造商:Texas Instruments 功能描述:NEW |
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