參數(shù)資料
        型號: L5986TR
        廠商: STMICROELECTRONICS
        元件分類: 穩(wěn)壓器
        英文描述: 3.9 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8
        封裝: 3 X 3 MM, 1.08 MM HEIGHT, ROHS COMPLIANT, VFQFP-8
        文件頁數(shù): 8/38頁
        文件大小: 1067K
        代理商: L5986TR
        Application information
        L5986
        16/38
        Doc ID 14971 Rev 3
        6.3
        Output capacitor selection
        The current in the capacitor has a triangular waveform which generates a voltage ripple
        across it. This ripple is due to the capacitive component (charge or discharge of the output
        capacitor) and the resistive component (due to the voltage drop across its ESR). So the
        output capacitor has to be selected in order to have a voltage ripple compliant with the
        application requirements.
        The amount of the voltage ripple can be calculated starting from the current ripple obtained
        by the inductor selection.
        Equation 9
        Usually the resistive component of the ripple is much higher than the capacitive one, if the
        output capacitor adopted is not a multi layer ceramic capacitor (MLCC) with very low ESR
        value.
        The output capacitor is important also for loop stability: it fixes the double LC filter pole and
        the zero due to its ESR. In Chapter 6.4, it will be illustrated how to consider its effect in the
        system stability.
        For example with VOUT = 3.3 V, VIN = 12 V, ΔIL = 0.75 A (resulting by the inductor value), in
        order to have a
        ΔV
        OUT = 0.01VOUT, if the multi layer ceramic capacitor are adopted, 11 F
        are needed and the ESR effect on the output voltage ripple can be neglected. In case of not
        negligible ESR (electrolytic or tantalum capacitors), the capacitor is chosen taking into
        account its ESR value. So in case of 330 F with ESR = 30 m
        Ω, the resistive component of
        the drop dominates and the voltage ripple is 22.5 mV
        .
        The output capacitor is also important to sustain the output voltage when a load transient
        with high slew rate is required by the load. When the load transient slew rate exceeds the
        system bandwidth the output capacitor provides the current to the load. So if the high slew
        rate load transient is required by the application the output capacitor and system bandwidth
        have to be chosen in order to sustain the load transient.
        In the table below some capacitor series are listed.
        Table 8.
        Output capacitors
        Manufacturer
        Series
        Cap value (
        μF)
        Rated voltage (V)
        ESR (m
        Ω)
        MURATA
        GRM32
        22 to 100
        6.3 to 25
        < 5
        GRM31
        10 to 47
        6.3 to 25
        < 5
        PANASONIC
        ECJ
        10 to 22
        6.3
        < 5
        EEFCD
        10 to 68
        6.3
        15 to 55
        SANYO
        TPA/B/C
        100 to 470
        4 to 16
        40 to 80
        TDK
        C3225
        22 to 100
        6.3
        < 5
        ΔV
        OUT
        ESR
        ΔI
        MAX
        ΔI
        MAX
        8C
        OUT
        f
        SW
        -------------------------------------
        +
        =
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