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CD43-4R7 bảng dữ liệu(PDF) 5 Page - Linear Technology |
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5 / 8 page 5 LT1945 1945f Choosing an Inductor Several recommended inductors that work well with the LT1945 are listed in Table 1, although there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts. Many different sizes and shapes are available. Use the equations and recommenda- tions in the next few sections to find the correct inductance value for your design. Table 1. Recommended Inductors PART VALUE ( µH) MAX DCR ( Ω) VENDOR LQH3C4R7 4.7 0.26 Murata LQH3C100 10 0.30 (714) 852-2001 LQH3C220 22 0.92 www.murata.com CD43-4R7 4.7 0.11 Sumida CD43-100 10 0.18 (847) 956-0666 CDRH4D18-4R7 4.7 0.16 www.sumida.com CDRH4D18-100 10 0.20 DO1608-472 4.7 0.09 Coilcraft DO1608-103 10 0.16 (847) 639-6400 DO1608-223 22 0.37 www.coilcraft.com Inductor Selection—Boost Regulator The formula below calculates the appropriate inductor value to be used for a boost regulator using the LT1945 (or at least provides a good starting point). This value pro- vides a good tradeoff in inductor size and system perfor- mance. Pick a standard inductor close to this value. A larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will in- crease the output voltage ripple without providing much additional output current. A smaller value can be used (especially for systems with output voltages greater than 12V) to give a smaller physical size. Inductance can be calculated as: L VV V I t OUT IN MIN D LIM OFF = −+ () where VD = 0.4V (Schottky diode voltage), ILIM = 350mA and tOFF = 400ns; for designs with varying VIN such as battery powered applications, use the minimum VIN value APPLICATIO S I FOR ATIO in the above equation. For most regulators with output voltages below 7V, a 4.7 µH inductor is the best choice, even though the equation above might specify a smaller value. This is due to the inductor current overshoot that occurs when very small inductor values are used (see Current Limit Overshoot section). For higher output voltages, the formula above will give large inductance values. For a 2V to 20V converter (typical LCD Bias application), a 21 µH inductor is called for with the above equation, but a 10 µH inductor could be used without excessive reduction in maximum output current. Inductor Selection—SEPIC Regulator The formula below calculates the approximate inductor value to be used for a SEPIC regulator using the LT1945. As for the boost inductor selection, a larger or smaller value can be used. L VV I t OUT D LIM OFF = + 2 Inductor Selection—Inverting Regulator The formula below calculates the appropriate inductor value to be used for an inverting regulator using the LT1945 (or at least provides a good starting point). This value provides a good tradeoff in inductor size and system performance. Pick a standard inductor close to this value (both inductors should be the same value). A larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will increase the output voltage ripple without providing much additional output current. A smaller value can be used (especially for systems with output voltages greater than 12V) to give a smaller physical size. Inductance can be calculated as: L VV I t OUT D LIM OFF = + 2 where VD = 0.4V (Schottky diode voltage), ILIM = 350mA and tOFF = 400ns. |
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