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參數(shù)資料
| 型號： | LM2731XMFX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.6/1.6 MHz Boost Converters With 22V Internal FET Switch in SOT-23 |
| 中文描述： | 2 A SWITCHING REGULATOR, 1850 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數(shù)： | 13/16頁 |
| 文件大?。?/td> | 528K |
| 代理商： | LM2731XMFX |
Application Hints
(Continued)
20059117
Basic Application Circuit
DUTY CYCLE
The maximum duty cycle of the switching regulator deter-
mines the maximum boost ratio of output-to-input voltage
that the converter can attain in continuous mode of opera-
tion. The duty cycle for a given boost application is defined
as:
This applies for continuous mode operation.
INDUCTANCE VALUE
The first question we are usually asked is: “How small can I
make the inductor” (because they are the largest sized
component and usually the most costly). The answer is not
simple and involves trade-offs in performance. Larger induc-
tors mean less inductor ripple current, which typically means
less output voltage ripple (for a given size of output capaci-
tor). Larger inductors also mean more load power can be
delivered because the energy stored during each switching
cycle is:
E = L/2 X (lp)
2
Where “l(fā)p” is the peak inductor current. An important point to
observe is that the LM2731 will limit its switch current based
on peak current. This means that since lp(max) is fixed,
increasing L will increase the maximum amount of power
available to the load. Conversely, using too little inductance
may limit the amount of load current which can be drawn
from the output.
Best performance is usually obtained when the converter is
operated in “continuous” mode at the load current range of
interest, typically giving better load regulation and less out-
put ripple. Continuous operation is defined as not allowing
the inductor current to drop to zero during the cycle. It should
be noted that all boost converters shift over to discontinuous
operation as the output load is reduced far enough, but a
larger inductor stays “continuous” over a wider load current
range.
To better understand these trade-offs, a typical application
circuit (5V to 12V boost with a 10 μH inductor) will be
analyzed. We will assume:
V
IN
= 5V, V
OUT
= 12V, V
DIODE
= 0.5V, V
SW
= 0.5V
Since the frequency is 1.6 MHz (nominal), the period is
approximately 0.625 μs. The duty cycle will be 62.5%, which
means the ON time of the switch is 0.390 μs. It should be
noted that when the switch is ON, the voltage across the
inductor is approximately 4.5V.
Using the equation:
V = L (di/dt)
We can then calculate the di/dt rate of the inductor which is
found to be 0.45 A/μs during the ON time. Using these facts,
we can then show what the inductor current will look like
during operation:
20059118
10 μH Inductor Current,
5V–12V Boost (LM2731X)
During the 0.390 μs ON time, the inductor current ramps up
0.176A and ramps down an equal amount during the OFF
time. This is defined as the inductor “ripple current”. It can
also be seen that if the load current drops to about 33 mA,
the inductor current will begin touching the zero axis which
means it will be in discontinuous mode. A similar analysis
can be performed on any boost converter, to make sure the
ripple current is reasonable and continuous operation will be
maintained at the typical load current values.
MAXIMUM SWITCH CURRENT
The maximum FET switch current available before the cur-
rent limiter cuts in is dependent on duty cycle of the appli-
cation. This is illustrated in the graphs below which show
typical values of switch current for both the "X" and "Y"
versions as a function of effective (actual) duty cycle:
L
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2731XMFX/NOPB | 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 |
| LM2731YEVAL | 功能描述:BOARD EVALUATION LM2731Y RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:PowerWise® 標(biāo)準(zhǔn)包裝:1 系列:- 主要目的:DC/DC，步降 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:3.3V 電流 - 輸出:3A 輸入電壓:4.5 V ~ 28 V 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):降壓 頻率 - 開關(guān):250kHz 板類型:完全填充 已供物品:板 已用 IC / 零件:L7981 其它名稱:497-12113STEVAL-ISA094V1-ND |
| LM2731YEVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM2731Y EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM2731YMF | 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 |
| LM2731YMF/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 0.6/1.6MHZ BOOST CONVERTER 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 |
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