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LTC3406B Datasheet(PDF) 8 Page - Linear Technology |
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LTC3406B Datasheet(HTML) 8 Page - Linear Technology |
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8 / 16 page  8 LTC3406B 3406bfa APPLICATIO S I FOR ATIO The basic LTC3406B application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of L followed by CIN and COUT. Inductor Selection For most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher VIN or VOUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is ∆IL = 240mA (40% of 600mA). ∆ = ()( ) − ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ I fL V V V L OUT OUT IN 1 1 (1) The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 720mA rated inductor should be enough for most applications (600mA + 120mA). For better efficiency, choose a low DC-resis- tance inductor. Inductor Core Selection Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy mate- rials are small and don’t radiate much energy, but gener- ally cost more than powdered iron core inductors with similar electrical characteristics. The choice of which style inductor to use often depends more on the price vs size requirements and any radiated field/EMI requirements than on what the LTC3406B requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3406B applications. Table 1. Representative Surface Mount Inductors PART VALUE DCR MAX DC SIZE NUMBER (µH) (Ω MAX) CURRENT (A) W × L × H (mm3) Sumida 1.5 0.043 1.55 3.8 × 3.8 × 1.8 CDRH3D16 2.2 0.075 1.20 3.3 0.110 1.10 4.7 0.162 0.90 Sumida 2.2 0.116 0.950 3.5 × 4.3 × 0.8 CMD4D06 3.3 0.174 0.770 4.7 0.216 0.750 Panasonic 3.3 0.17 1.00 4.5 × 5.4 × 1.2 ELT5KT 4.7 0.20 0.95 Murata 1.0 0.060 1.00 2.5 × 3.2 × 2.0 LQH3C 2.2 0.097 0.79 4.7 0.150 0.65 CIN and COUT Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: CI VV V V IN OMAX OUT IN OUT IN required IRMS ≅ − () [] 12 / This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is com- monly used for design because even significant deviations do not offer much relief. Note that the capacitor manufacturer’s ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Always consult the manufac- turer if there is any question. The selection of COUT is driven by the required effective series resistance (ESR). |
Similar Part No. - LTC3406B_15 |
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Similar Description - LTC3406B_15 |
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