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LTC3406AB Datasheet(PDF) 8 Page - Linear Technology |
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LTC3406AB Datasheet(HTML) 8 Page - Linear Technology |
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8 / 16 page  LTC3406AB 8 3406abfa The basic LTC3406AB application circuit is shown on the front page. External component selection is driven by the load requirement and begins with the selection of L fol- lowed 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 cur- rent as shown in equation 1. A reasonable starting point for setting ripple current is ΔIL = 240mA (40% of 600mA). Δ= ()( ) − ⎛ ⎝⎜ ⎞ ⎠⎟ 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-resistance inductor. Inductor Core Selection Different core materials and shapes will change the size/current and price/current relationship of an induc- tor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don’t radiate much energy, but generally 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 require- ments than on what the LTC3406AB requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3406AB applications. APPLICATIONS INFORMATION 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 IN OMAX OUT IN OUT required IRMS ≅ − () ⎡⎣ ⎤⎦ 1/2 2 VIN This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant de- viations 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 tem- perature than required. Always consult the manufacturer if there is any question. The selection of COUT is driven by the required effective series resistance (ESR). Table 1. Representative Surface Mount Inductors PART NUMBER VALUE (μH) DCR (Ω MAX) MAX DC CURRENT (A) SIZE W × L × H (mm3) Sumida CDRH3D16 1.5 2.2 3.3 4.7 0.043 0.075 0.110 0.162 1.55 1.20 1.10 0.90 3.8 × 3.8 × 1.8 Sumida CMD4D06 2.2 3.3 4.7 0.116 0.174 0.216 0.950 0.770 0.750 3.5 × 4.3 × 0.8 Panasonic ELT5KT 3.3 4.7 0.17 0.20 1.00 0.95 4.5 × 5.4 × 1.2 Murata LQH32CN 1.0 2.2 4.7 0.060 0.097 0.150 1.00 0.79 0.65 2.5 × 3.2 × 2.0 |
Similar Part No. - LTC3406AB_15 |
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Similar Description - LTC3406AB_15 |
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