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參數(shù)資料
| 型號(hào)： | LM2733XMF |
| 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 40V Internal FET |
| 中文描述： | 1.5 A SWITCHING REGULATOR, 1850 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁(yè)數(shù)： | 10/13頁(yè) |
| 文件大?。?/td> | 507K |
| 代理商： | LM2733XMF |
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Application Hints
(Continued)
20055405
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.
The equation shown for calculating duty cycle incorporates
terms for the FET switch voltage and diode forward voltage.
The actual duty cycle measured in operation will also be
affected slightly by other power losses in the circuit such as
wire losses in the inductor, switching losses, and capacitor
ripple current losses from self-heating. Therefore, the actual
(effective) duty cycle measured may be slightly higher than
calculated to compensate for these power losses. A good
approximation for effctive duty cycle is :
DC (eff) = (1 - Efficiency x (V
IN
/V
OUT
))
Where the efficiency can be approximated from the curves
provided.
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 tradeoffs 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 LM2733 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 tradeoffs, 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:
20055412
10 μH Inductor Current,
5V–12V Boost (LM2733X)
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.
L
www.national.com
10
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| LM2734YMK | Thin SOT23 1A Load Step-Down DC-DC Regulator |
| LM2734XMKX | Thin SOT23 1A Load Step-Down DC-DC Regulator |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2733XMF/MEY8 | 制造商:Texas Instruments 功能描述: |
| LM2733XMF/NOPB | 功能描述:DC/DC 開(kāi)關(guān)控制器 0.6/1.6MHZ BOOST CONVERTER 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 |
| LM2733XMFNOPB | 制造商:National Semiconductor 功能描述:Conv DC-DC Single Step Up 2.7V to 14V 5-Pin SOT-23 T/R |
| LM2733XMF-NOPB | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM2733 0.6/1.6 MHz Boost Converters With 40V Internal FET Switch in SOT-23 |
| LM2733XMFX | 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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