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SC196A Datasheet(PDF) 9 Page - Semtech Corporation |
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SC196A Datasheet(HTML) 9 Page - Semtech Corporation |
9 / 17 page 9 © 2008 Semtech Corp. www.semtech.com SC196A PRELIMINARY POWER MANAGEMENT Applications Information (Cont.) Table 2 — Recommended Capacitors Note: Where PSAVE operation is required, 22μF must be used for C OUT. Manufacturer/Part # Value (μF) Rated Voltage (VDC) Temperature Characteristic Case Size Murata GRM21BR60J226ME39L 22 6.3 X5R 0805 Murata GRM188R60J106 MKE19 10 6.3 X5R 0603 TDK C2012X5R0J106K 10 6.3 X5R 0603 Inductor Selection The SC196A is designed for use with a 4.7μH inductor. The magnitude of the inductor current ripple is dependent on the inductor value and can be determined by the following equation: OSC N I OUT OUT L f L V V 1 V I This equation demonstrates the relationship between input voltage, output voltage, and inductor ripple current. The inductor should have a low DCR to minimize the conduction losses and maximize efficiency. As a minimum requirement, the DC current rating of the inductor should be equal to the maximum load current plus half of the inductor current ripple, as shown by the following equation: 2 I I I L ) MAX ( OUT LPK Final inductor selection will depend on various design considerations, such as efficiency, EMI, size and cost. Table 1 lists the manufacturers of practical inductor options. C IN Selection The source input current to a buck converter is non- continuous. To prevent large input voltage ripple, a low ESR ceramic capacitor is required. A minimum value of 10μF should be used for sufficient input voltage filtering, and a 22μF should be used for improved input voltage filtering. C OUT Selection The internal compensation is designed to work with a certain output filter corner frequency, which is defined by the equation: OUT C C L 2 1 f This single pole filter is designed to operate with a minimum output capacitor value of 10μF. Larger output capacitor values will improve transient performance. If PSAVE operation is required, the minimum capacitor value is 22μF. Output voltage ripple is a combination of the voltage ripple from the charge - discharge cycle of the output capacitor and the voltage created by the inductor ripple current passing through the output capacitor ESR. Selecting an output capacitor with a low ESR will reduce the output voltage ripple component, as can be seen in the following equation: Capacitors with X7R or X5R ceramic dielectric are strongly recommended for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coefficients make them unsuitable for this application. Table 2 lists the manufacturers of recommended capacitor options. ) COUT ( ) ripple ( L ) ESR ( OUT ESR I V Table 1 — Recommended Inductors Manufacturer/Part # Value (μH) DCR (Ω) Rated Current (A) Tolerance (%) Dimensions LxWxH (mm) BI Technologies HM66404R1 4.1 0.057 1.95 20 5.7 × 5.7 ×2.0 Coilcraft D01608C-472ML 4.7 0.09 1.5 20 6.6 × 4.5 × 3.0 TDK VLCF4020T- 4R7N1R2 4.7 0.098 1.24 30 4.0 × 4.0 × 2.0 Taiyo Yuden LMNP04SB4R7N 4.7 0.050 1.2 30 5.0 × 5.0 × 2.0 TOKO D52LC 4.7 0.087 1.14 20 5.0 × 5.0 × 2.0 Sumida CDRH3D16 4.7 0.050 1.2 30 3.8 × 3.8 × 1.8 Coilcraft LPS3015 4.7 0.2 1.1 20 3.0 × 3.0 × 1.5 Note: recommended Inductors do not necessarily guarantee rated perfor- mance of the part. |
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