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  • 参数资料
    型号: LM2574M-3.3LM2574M-5.0
    厂商: National Semiconductor Corporation
    英文描述: SIMPLE SWITCHERT 0.5A Step-Down Voltage Regulator(639.73 k)
    中文描述: 简单SWITCHERT 0.5A的降压稳压器(639.73十一)
    文件页数: 15/24页
    文件大?。?/td> 397K
    代理商: LM2574M-3.3LM2574M-5.0
    LM2574
    15
    MOTOROLA ANALOG IC DEVICE DATA
    EXTERNAL COMPONENTS
    Input Capacitor (Cin)
    The Input Capacitor Should Have a Low ESR
    For stable operation of the switch mode converter a low
    ESR (Equivalent Series Resistance) aluminium or solid
    tantalum bypass capacitor is needed between the input pin
    and the ground pin, to prevent large voltage transients from
    appearing at the input. It must be located near the regulator
    and use short leads. With most electrolytic capacitors, the
    capacitance value decreases and the ESR increases with
    lower temperatures. For reliable operation in temperatures
    below –25
    °
    C larger values of the input capacitor may be
    needed. Also paralleling a ceramic or solid tantalum
    capacitor will increase the regulator stability at cold
    temperatures.
    RMS Current Rating of Cin
    The important parameter of the input capacitor is the RMS
    current rating. Capacitors that are physically large and have
    large surface area will typically have higher RMS current
    ratings. For a given capacitor value, a higher voltage
    electrolytic capacitor will be physically larger than a lower
    voltage capacitor, and thus be able to dissipate more heat to
    the surrounding air, and therefore will have a higher RMS
    current rating. The consequences of operating an electrolytic
    capacitor beyond the RMS current rating is a shortened
    operating life. In order to assure maximum capacitor
    operating lifetime, the capacitor’s RMS ripple current rating
    should be:
    Irms
    1.2 x d x ILoad
    where d is the duty cycle, for a continuous mode buck
    regulator
    ton
    T
    d
    Vout
    Vin
    and d
    ton
    T
    |Vout|
    |Vout|
    Vin
    for a buck–boost regulator.
    Output Capacitor (Cout)
    For low output ripple voltage and good stability, low ESR
    output capacitors are recommended. An output capacitor has
    two main functions: it filters the output and provides regulator
    loop stability. The ESR of the output capacitor and the
    peak–to–peak value of the inductor ripple current are the
    main factors contributing to the output ripple voltage value.
    Standard aluminium electrolytics could be adequate for some
    applications but for quality design, low ESR types are
    recommended.
    An aluminium electrolytic capacitor’s ESR value is related
    to many factors, such as the capacitance value, the voltage
    rating, the physical size and the type of construction. In most
    cases, the higher voltage electrolytic capacitors have lower
    ESR value. Often capacitors with much higher voltage
    ratings may be needed to provide low ESR values, that are
    required for low output ripple voltage.
    The Output Capacitor Requires an ESR Value that has
    an Upper and Lower Limit
    As mentioned above, a low ESR value is needed for low
    output ripple voltage, typically 1% to 2% of the output voltage.
    But if the selected capacitor’s ESR is extremely low (below
    0.03
    ), there is a possibility of an unstable feedback loop,
    resulting in oscillation at the output. This situation can occur
    when a tantalum capacitor, that can have a very low ESR, is
    used as the only output capacitor.
    At Low Temperatures, Put in Parallel Aluminium
    Electrolytic Capacitors with Tantalum Capacitors
    Electrolytic capacitors are not recommended for
    temperatures below –25
    °
    C. The ESR rises dramatically at
    cold temperatures and typically rises 3 times at –25
    °
    C and as
    much as 10 times at –40
    °
    C. Solid tantalum capacitors have
    much better ESR spec at cold temperatures and are
    recommended for temperatures below –25
    °
    C. They can be
    also used in parallel with aluminium electrolytics. The value
    of the tantalum capacitor should be about 10% or 20% of the
    total capacitance. The output capacitor should have at least
    50% higher RMS ripple current rating at 52 kHz than the
    peak–to–peak inductor ripple current.
    Catch Diode
    Locate the Catch Diode Close to the LM2574
    The LM2574 is a step–down buck converter, it requires a
    fast diode to provide a return path for the inductor current
    when the switch turns off. This diode must be located close to
    the LM2574 using short leads and short printed circuit traces
    to avoid EMI problems.
    Use a Schottky or a Soft Switching
    Ultra–Fast Recovery Diode
    Since the rectifier diodes are very significant source of
    losses within switching power supplies, choosing the rectifier
    that best fits into the converter design is an important
    process. Schottky diodes provide the best performance
    because of their fast switching speed and low forward
    voltage drop.
    They provide the best efficiency especially in low output
    voltage applications (5.0 V and lower). Another choice could
    be Fast–Recovery, or Ultra–Fast Recovery diodes. It has to
    be noted, that some types of these diodes with an abrupt
    turnoff characteristic may cause instability or EMI troubles.
    A fast–recovery diode with soft recovery characteristics
    can better fulfill some quality, low noise design requirements.
    Table 1 provides a list of suitable diodes for the LM2574
    regulator. Standard 50/60 Hz rectifier diodes, such as the
    1N4001 series or 1N5400 series are NOT suitable.
    Inductor
    The magnetic components are the cornerstone of all
    switching power supply designs. The style of the core and the
    winding technique used in the magnetic component’s design
    have a great influence on the reliability of the overall power
    supply.
    Using an improper or poorly designed inductor can cause
    high voltage spikes generated by the rate of transitions in
    current within the switching power supply, and the possibility
    of core saturation can arise during an abnormal operational
    mode. Voltage spikes can cause the semiconductors to enter
    avalanche breakdown and the part can instantly fail if enough
    energy is applied. It can also cause significant RFI (Radio
    Frequency Interference) and EMI (Electro–Magnetic
    Interference) problems.
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    相关代理商/技术参数
    参数描述
    LM2574M-5 制造商:NSC 制造商全称:National Semiconductor 功能描述:SIMPLE SWITCHERT 0.5A Step-Down Voltage Regulator(639.73 k)
    LM2574M-5.0 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
    LM2574M-5.0 制造商:Texas Instruments 功能描述:SWITCHING REG 0.5A 5.0V SMD 2574
    LM2574M-5.0/NOPB 功能描述:直流/直流开关转换器 0.5A STEP-DOWN VLTG REG RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
    LM2574M-ADJ 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
  • 你距鸟巢的距离,只有21.0975公里! 2019-04-24
  • 王牧的专栏作者中国国家地理网 2019-04-24
  • 每个具体事物的本质联系即规律都是普遍规律的特殊表现47 2019-04-15
  • 全论坛的人都跟你一样不会算8421,把自己的祖宗十八代都算没了?[大笑] 2019-04-15
  • 中国对农产品、汽车等500亿美元美国进口商品加征关税 2019-04-13
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  • 永济:雨天采摘黄花菜 多元增收过端午 2019-04-09
  • 一个企业里的劳动力,有可能被叫做职工,意指按职责做事的人,也可能被叫做劳工,意指按劳动力做事的人。不同的称呼,体现了不同的企业性质与追求。懂这点,你才明白这“意 2019-04-08
  • 只用把这2味调料倒进马桶里,马桶立马洁净如新,一点臭味都没有 2019-04-08
  • 上海合作组织青岛峰会举行 2019-04-05
  • [大笑]那是你认的远祖也,跟咱没关系! 2019-04-02
  • 玉带串明珠 蛟龙贴地飞 2019-04-02
  • 山东十一运夺金开奖走势图 足彩开奖 双色球复试有计算公式吗 湖南幸运赛车开奖 pc蛋蛋机器人怎么破解 大神吧幸运28 易算北京赛车pk10破解 新疆时时彩开奖号 安徽省福利彩票走势图 香港自小姐一肖中特马 新疆时时彩开奖结果彩票控 福彩3d图谜总汇 15选5走势图彩经网 湖南快乐十分 pk10单双投注方法 秒速时时彩是国家的吗