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LTC3418 датащи(PDF) 14 Page - Linear Technology |
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LTC3418 датащи(HTML) 14 Page - Linear Technology |
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14 / 20 page ![]() 14 LTC3418 3418f APPLICATIO S I FOR ATIO Using a 0.2µH inductor results in a maximum ripple current of: ∆ = () µ () ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ = I V MHz H V V A L 25 10 2 1 25 33 303 . . – . . . COUT will be selected based on the ESR that is required to satisfy the output voltage ripple requirement and the bulk capacitance needed for loop stability. For this design, five 100µF ceramic capacitors will be used. CIN should be sized for a maximum current rating of: IA V V V V A RMS RMS = () ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ = 8 25 33 33 25 13 43 . . . . –. Decoupling the PVIN and SVIN pins with four 100µF capacitors is adequate for this application. The burst clamp and output voltage can now be pro- grammed by choosing the values of R1, R2 and R3. The voltage on the MODE pin will be set to 0.67V by the resistor divider consisting of R2 and R3. A burst clamp voltage of 0.67V will set the minimum inductor current, IBURST, to approximately 1.2A. If we set the sum of R2 and R3 to 200k, then the following equations can be solved. RR k R R V V 2 3 200 1 2 3 08 067 += += . . The two equations shown above result in the following values for R2 and R3: R2 = 33.2k, R3 = 169k. The value of R1 can now be determined by solving the equation: 1 1 202 2 25 08 1 430 += = R k V V Rk . . . A value of 432k will be selected for R1. Figure 4 shows the complete schematic for this design example. PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SVIN TRACK PGOOD RUN/SS ITH RT SGND PGND PGND PGND PGND 1 2 11 12 20 21 30 31 25 27 38 37 36 34 33 32 19 18 16 3 4 9 10 22 23 28 29 24 35 5 7 26 6 8 13 14 15 17 SW SW SW SW SW SW SW SW VFB SYNC/MODE PGND PGND PGND PGND PGND PGND PGND PGND VREF LTC3418 L1 0.2µH C1 22pF X7R COUT 100µF ×5 CREF 2.2µF X7R CIN 100µF ×4 VIN 3.3V VOUT 2.5V 8A R1 432k RPG 100k RSS 2.2M CSS 1000pF X7R CITH 820pF X7R RITH 7.5k RSVIN 100Ω ROSC 69.8k R2 33.2k R3 169k VREF C1 47pF X7R 3418 F04 CIN, COUT: AVX 18126D107MAT L1: TOKO FDV0620-R20M CSVIN 1µF X7R Figure 4. 2.5V, 8A Regulator at 1MHz, Burst Mode Operation |
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