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SC192IMLTR Datasheet(PDF) 11 Page - Semtech Corporation |
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SC192IMLTR Datasheet(HTML) 11 Page - Semtech Corporation |
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11 / 15 page  11 © 2007 Semtech Corp. www.semtech.com SC192 POWER MANAGEMENT Inductor Selection The inductor values listed in Table 1 will work for nearly all combinations of output current and output voltages. After selecting 4.7uH or 10uH for the inductor value two additional inductor parameters should be considered. The current rating of the inductor and the DC resistance. The DC resistance has a great impact on efficiency due to copper losses. However, small inductors tend to have higher DC resistance. Therefore a compromise between size and efficiency will need to be made. The inductor current must be chosen to prevent the in- ductor from saturation. The most conservative approach would be to select an inductor with a saturation current slightly above the maximum current capability of the SC192 which is 1.56A peak current for ILIM = Vin or 780mA for ILIM = GND. A more accurate design of the inductor would be to rate the inductor for the maximum output current plus the inductor ripple current that can be calculated as follows: 2 I I I L ) O(MAX L(MAX) Δ + = OUT IN OUT L V f L V V - 1 I • ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ • = Δ f = Switching frequency L = Inductor Value ΔI L= Peak-to-peak inductor ripple current I L = Maximum inductor current V OUT = Output voltage V IN = Input voltage C OUT = Output Capacitance I OUT = Output Current I OUT(MAX) = Maximum DC Output Current Output Capacitor Selection Because the SC192 has external compensation avail- able, low ESR ceramic capacitors can be used. This elimi- nates the need for bulky tantalum capacitors. Values for the output capacitors in Table 1 will work for nearly all combinations of output current and output voltages. The equation for determining the size of the output capaci- tor in terms of minimizing the ripple voltage is given as follows: ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + • • • Δ = Δ ESR f C 8 1 I V OUT L O Input Capacitor Selection The input ripple current can be reduced with properly selecting the input capacitor. Again, values for the input capacitors in Table 1 will work for nearly all combina- tions of input current and output voltages. The input ca- pacitor should be rated for the maximum input ripple current calculated as: PSAVE, Cout = 4.7uF, Lout = 4.7uH PWM, Cout = 4.7uF, Lout = 4.7uH Applications Information Cont. |
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