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參數(shù)資料
| 型號(hào)： | LM2731XMF |
| 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)： | 12/16頁 |
| 文件大?。?/td> | 528K |
| 代理商： | LM2731XMF |
Application Hints
SELECTING THE EXTERNAL CAPACITORS
The best capacitors for use with the LM2731 are multi-layer
ceramic capacitors. They have the lowest ESR (equivalent
series resistance) and highest resonance frequency which
makes them optimum for use with high frequency switching
converters.
When selecting a ceramic capacitor, only X5R and X7R
dielectric types should be used. Other types such as Z5U
and Y5F have such severe loss of capacitance due to effects
of temperature variation and applied voltage, they may pro-
vide as little as 20% of rated capacitance in many typical
applications. Always consult capacitor manufacturer’s data
curves before selecting a capacitor. High-quality ceramic
capacitors can be obtained from Taiyo-Yuden, AVX, and
Murata.
SELECTING THE OUTPUT CAPACITOR
A single ceramic capacitor of value 4.7 μF to 10 μF will
provide sufficient output capacitance for most applications. If
larger amounts of capacitance are desired for improved line
support and transient response, tantalum capacitors can be
used. Aluminum electrolytics with ultra low ESR such as
Sanyo Oscon can be used, but are usually prohibitively
expensive. Typical AI electrolytic capacitors are not suitable
for switching frequencies above 500 kHz due to significant
ringing and temperature rise due to self-heating from ripple
current. An output capacitor with excessive ESR can also
reduce phase margin and cause instability.
In general, if electrolytics are used, it is recommended that
they be paralleled with ceramic capacitors to reduce ringing,
switching losses, and output voltage ripple.
SELECTING THE INPUT CAPACITOR
An input capacitor is required to serve as an energy reservoir
for the current which must flow into the coil each time the
switch turns ON. This capacitor must have extremely low
ESR, so ceramic is the best choice. We recommend a
nominal value of 2.2 μF, but larger values can be used. Since
this capacitor reduces the amount of voltage ripple seen at
the input pin, it also reduces the amount of EMI passed back
along that line to other circuitry.
FEED-FORWARD COMPENSATION
Although internally compensated, the feed-forward capacitor
Cf is required for stability (see
Basic Application Circuit
).
Adding this capacitor puts a zero in the loop response of the
converter. The recommended frequency for the zero fz
should be approximately 6 kHz. Cf can be calculated using
the formula:
Cf = 1 / (2 X
π
X R1 X fz)
SELECTING DIODES
The external diode used in the typical application should be
a Schottky diode. A 20V diode such as the MBR0520 is
recommended.
The MBR05XX series of diodes are designed to handle a
maximum average current of 0.5A. For applications exceed-
ing 0.5A average but less than 1A, a Microsemi UPS5817
can be used.
LAYOUT HINTS
High frequency switching regulators require very careful lay-
out of components in order to get stable operation and low
noise. All components must be as close as possible to the
LM2731 device. It is recommended that a 4-layer PCB be
used so that internal ground planes are available.
As an example, a recommended layout of components is
shown:
20059116
Recommended PCB Component Layout
Some additional guidelines to be observed:
1.
Keep the path between L1, D1, and C2 extremely short.
Parasitic trace inductance in series with D1 and C2 will
increase noise and ringing.
2.
The feedback components R1, R2 and CF must be kept
close to the FB pin of U1 to prevent noise injection on
the FB pin trace.
3.
If internal ground planes are available (recommended)
use vias to connect directly to ground at pin 2 of U1, as
well as the negative sides of capacitors C1 and C2.
SETTING THE OUTPUT VOLTAGE
The output voltage is set using the external resistors R1 and
R2 (see
Basic Application Circuit
). A value of approximately
13.3 k
is recommended for R2 to establish a divider current
of approximately 92 μA. R1 is calculated using the formula:
R1 = R2 X (V
OUT
/1.23 1)
SWITCHING FREQUENCY
The LM2731 is provided with two switching frequencies: the
“X” version is typically 1.6 MHz, while the “Y” version is
typically 600 kHz. The best frequency for a specific applica-
tion must be determined based on the trade-offs involved:
Higher switching frequency means the inductors and capaci-
tors can be made smaller and cheaper for a given output
voltage and current. The down side is that efficiency is
slightly lower because the fixed switching losses occur more
frequently and become a larger percentage of total power
loss. EMI is typically worse at higher switching frequencies
because more EMI energy will be seen in the higher fre-
quency spectrum where most circuits are more sensitive to
such interference.
L
www.national.com
12
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2731XMF/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 |
| LM2731XMFX | 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 |
| 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(píng)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(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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