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LTC3544 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3544 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  LTC3544 10 3544fa The basic LTC3544 application circuit is shown on the first page of this data sheet. External component selection is driven by the load requirement and begins with the selec- tion 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 10μH. Its value is chosen based on the desired ripple current. Large inductor values lower ripple current and small inductor values 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 for the 300mA regulator is ΔIL = 120mA (40% of 300mA). ΔI L V V V L OUT OUT IN = ()( ) ⎛ ⎝⎜ ⎞ ⎠⎟ 1 1 ƒ – (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 360mA rated inductor should be enough for most applications (300mA + 60mA). For better efficiency, choose a low DCR 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 requirements than on what the LTC3544 requires to operate. Table 1 shows typical surface mount inductors that work well in LTC3544 applications. APPLICATIONS INFORMATION Table 1. Representative Surface Mount Inductors Part Number Value (μH) DCR (Ω MAX) MAX DC CURRENT (A) W × L × H (mm3) Sumida CDH2D09B 10 6.4 4.7 3.3 0.47 0.32 0.218 0.15 0.48 0.6 0.7 0.85 3.0 × 2.8 × 1.0 Wurth TPC744029 10 6.8 4.7 3.3 0.50 0.38 0.210 0.155 0.50 0.65 0.80 0.95 2.8 × 2.8 × 1.35 TDK VLF3010AT 10 6.8 4.7 3.3 0.67 0.39 0.28 0.17 0.49 0.61 0.70 0.87 2.8 × 2.6 × 1.0 CIN and COUT Selection In continuous mode, a worst-case estimate for the input current ripple can be determined by assuming that the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN, and amplitude IOUT(MAX). 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: II VV V V RMS OUT MAX OUT IN OUT IN ≅ () () – This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design. Note that the capacitor manufacturer’s ripple current ratings are often based on 2000 hours of life (non-ceramic capacitors). This makes it advisable to further de-rate the capacitor, or choose a capacitor rated at a higher temperature than required. Always consult the manufacturer if there is any question. The selection of COUT is driven by the required effective series resistance (ESR). Typically, once the ESR require- ment for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple ΔVOUT is determined by: ΔΔ V I ESR C OUT L OUT ≅+ ⎛ ⎝⎜ ⎞ ⎠⎟ 1 8• • ƒ where f = operating frequency, COUT = output capacitance and ΔIL = ripple current in the inductor. For a fixed output |
Similar Part No. - LTC3544_15 |
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Similar Description - LTC3544_15 |
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