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LTC3854EMSE 数据表(PDF) 20 Page - Linear Technology |
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LTC3854EMSE 数据表(HTML) 20 Page - Linear Technology |
20 / 28 page LTC3854 0 3854fa applicaTions inForMaTion Design Example Consider the design of a 1.2V, 15A buck regulator with a VIN range of 4.5V to 28V using a DCR sensing scheme. Inductor Selection Assuming an inductor ripple of 40% of IOUT, L can be calculated for the worst case of VIN = VIN(MAX). LMIN = 1 ∆IL • fSW • VOUT 1− VOUT VIN(MAX) LMIN = 1 0.40 • 15A • 400kHz • 1.2V • 1 − 1.2V 20V LMIN = 0.47µH Next, determine the DCR of the inductor. When provided, use the manufacturer’s maximum value, usually given at 25°C. Increase this value to account for the temperature coefficientofresistance,whichisapproximately0.4%/°C.A conservative value for TLMAX is 100°C which corresponds to a delta of 0.3. To allow the converter to source 15A with aninductortemperatureof100°Cwithouthittingmaximum current limit we need a DCR at 25°C of: DCR(25°C) = 0.8 • VSENSE(MAX) IMAX + ∆IL 2 •(1 + δ) DCR(25°C) = 0.8 • 50mV 15A + 15A • 0.4 2 •(1 + 0.3) DCR(25°C) = 1.7m Ω The 0.56µH inductor from the IHLP4040DZ-01 series has a typical DCR of 1.7mΩ and a maximum of 1.8mΩ and as ISAT of 49A. The saturation current is well above our operating current maximum. The maximum inductor will be the DC value plus one half the ripple current. Using this inductor gives an inductor ripple current of 6A (keeping the ripple current high will also help insure the minimum on-time requirement of 75ns is not violated). tON(MIN) = VOUT VIN(MAX) • fSW tON(MIN) = 1.2V 20V • 400kHz tON(MIN) =150ns To choose R1 for DCR sensing we use: R1• C1 = L DCR at 25°C Choosing C1 = 100nF and using the maximum DCR value at 25°C, we get: R1 = 0.56µH 1.8m Ω •100nF R1 = 3.11k Choose 3.09k. Output Capacitor Selection The output voltage AC ripple due to capacitive impedance and ESR in normal continuous mode operation can be calculated from: ∆VOUT = ∆IL ESR+ 1 8 • fSW •COUT The second term is the AC capacitive impedance part of the above equation and used alone will yield a minimum COUT of: COUT > ∆IL 8 • fSW • ∆VOUT COUT > 0.4 • 15A 8 • 400kHz • 0.01• 1.2V COUT >156µF |
类似零件编号 - LTC3854EMSE |
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类似说明 - LTC3854EMSE |
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