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SP6659 Datasheet(PDF) 9 Page - Sipex Corporation |
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SP6659 Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 11 page  9 Date: 9/25/06 Rev C SP6659 1.5MHz, 600mA Synchronous Buck Regulator © 2006 Sipex Corporation THEORY OF OPERATION choose an inductor with DC series resis- tance in the 50mΩ to 150mΩ range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100mΩ. The DC cur- rent rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (600mA+105mA). Table 1 lists some typical surface mount inductors that meet target applications for the SP6659. Table 1: Typical Surface Mount Inductors ________________ INPUT CAPACITOR SELECTION The input capacitor reduces the surge cur- rent drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current from passing to the input. A low ESR (Equiva- lent Series Resistance) input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielec- trics are highly recommended because of their low ESR and small temperature coeffi- cients. A 4.7μF ceramic capacitor for most applications is sufficient. ______________ OUTPUT CAPACITOR SELECTION The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capaci- tor must have low impedance at the switch- ing frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripple ΔVOUT is determined by: X {ESR + } 1 (8X ƒ OSC X COUT) ΔVOUT ≤ VOUT X (VINMax - VOUT) VINMax X L X ƒ OSC SP6659 Inductor Selection Chart Murata LQH32CN2R2M11 1.0 78 1 3.2x2.5x1.55 Murata LQH32CN2R2M11 2.2 126 0. 79 3.2x2.5x1.55 Murata LQH32CN4R7M11 4.7 1 9 5 0.6 5 3.2x2.5x1.55 1.4 56.2 2.52 2.2 71.2 1.5 3.3 86.2 1.44 4.7 108.7 1.15 1.5 2.2 75 1.32 3.3 110 1.04 4.7 162 0.84 1.5 120 1.29 2.2 140 1.14 3.3 180 0.98 4.7 240 0.79 Inductor in Bold is used on the SP6659EB evaluation Board 4.7x4.7x2.0 Size WxLxH (mm) Sumida CR43 Sumida CDRH4D18 Toko D312C Part # Inductor (µH) Max DCR (mΩ) Rated DC Current (Amps) 4.5x4.0x3.5 3.6x3.6x1.2 |
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