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參數(shù)資料
| 型號(hào)： | LM20242MH |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 36V, 2A PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| 中文描述： | 4.65 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | TSSOP-20 |
| 文件頁(yè)數(shù)： | 11/20頁(yè) |
| 文件大?。?/td> | 384K |
| 代理商： | LM20242MH |
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Design Guide
This section walks the designer through the steps necessary
to select the external components to build a fully functional
power supply. As with any DC-DC converter numerous trade-
offs are possible to optimize the design for efficiency, size, or
performance. These will be taken into account and highlight-
ed throughout this discussion. To facilitate component selec-
tion discussions the circuit shown in
Figure 2
below may be
used as a reference. Unless otherwise indicated all formulas
assume units of amps (A) for current, farads (F) for capaci-
tance, henries (H) for inductance and volts (V) for voltages.
30031429
FIGURE 2. Typical Application Circuit
The first equation to calculate for any buck converter is duty-
cycle. Ignoring conduction losses associated with the FETs
and parasitic resistances it can be approximated by:
INDUCTOR SELECTION (L)
The inductor value is determined based on the operating fre-
quency, load current, ripple current and duty cycle.
The inductor selected should have a saturation current rating
greater than the peak current limit of the device. Keep in mind
the specified current limit does not account for delay of the
current limit comparator, therefore the current limit in the ap-
plication may be higher than the specified value. To optimize
the performance and prevent the device from entering current
limit at maximum load, the inductance is typically selected
such that the ripple current,
Δ
i
L
, is not greater than 30% of the
rated output current.
Figure 3
illustrates the switch and in-
ductor ripple current waveforms. Once the input voltage, out-
put voltage, operating frequency and desired ripple current
are known, the minimum value for the inductor can be calcu-
lated by the formula shown below:
30031467
FIGURE 3. Switch and Inductor Current Waveforms
If needed, slightly smaller value inductors can be used, how-
ever, the peak inductor current, I
+ Δ
i
/2, should be kept
below the peak current limit of the device. In general, the in-
ductor ripple current,
Δ
i
L
, should be more than 10% of the
rated output current to provide adequate current sense infor-
mation for the current mode control loop. If the ripple current
in the inductor is too low, the control loop will not have suffi-
cient current sense information and can be prone to instability.
OUTPUT CAPACITOR SELECTION (C
OUT
)
The output capacitor, C
OUT
, filters the inductor ripple current
and provides a source of charge for transient load conditions.
A wide range of output capacitors may be used with the
LM20242 that provide excellent performance. The best per-
formance is typically obtained using ceramic, SP or OSCON
type chemistries. Typical trade-offs are that the ceramic ca-
pacitor provides extremely low ESR to reduce the output
ripple voltage and noise spikes, while the SP and OSCON
capacitors provide a large bulk capacitance in a small volume
for transient loading conditions.
When selecting the value for the output capacitor, the two
performance characteristics to consider are the output volt-
age ripple and transient response. The output voltage ripple
can be approximated by using the following formula.
11
www.national.com
L
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM20242MH/NOPB | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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 |
| LM20242MHE | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP T/R |
| LM20242MHE/NOPB | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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 |
| LM20242MHX | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP T/R |
| LM20242MHX/NOPB | 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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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