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LT1933ES6-TRPBF Datasheet(PDF) 8 Page - Linear Technology |
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LT1933ES6-TRPBF Datasheet(HTML) 8 Page - Linear Technology |
8 / 20 page LT1933 8 1933fd APPLICATIONS INFORMATION Table 1.Inductor Vendors Vendor URL Part Series Inductance Range (μH) Size (mm) Coilcraft www.coilcraft.com D01608C 10 to 22 2.9 × 4.5 × 6.6 MSS5131 10 to 22 3.1 × 5.1 × 5.1 MSS6122 10 to 33 2.2 × 6.1 × 6.1 Sumida www.sumida.com CR43 10 to 22 3.5 × 4.3 × 4.8 CDRH4D28 10 to 33 3.0 × 5.0 × 5.0 CDRH5D28 22 to 47 3.0 × 5.7 × 5.7 Toko www.toko.com D52LC 10 to 22 2.0 × 5.0 × 5.0 D53LC 22 to 47 3.0 × 5.0 × 5.0 Würth Elektronik www.we-online.com WE-TPC MH 10 to 22 2.8 × 4.8 × 4.8 WE-PD4 S 10 to 22 2.9 × 4.5 × 6.6 WE-PD2 S 10 to 47 3.2 × 4.0 × 4.5 saturation current should be about 30% higher. For robust operation in fault conditions the saturation current should be ~1A. To keep efficiency high, the series resistance (DCR) should be less than 0.2Ω. Table 1 lists several vendors and types that are suitable. Of course, such a simple design guide will not always re- sult in the optimum inductor for your application. A larger value provides a slightly higher maximum load current, and will reduce the output voltage ripple. If your load is lower than 500mA, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is OK, but further reduces maximum load current. For details of maximum output current and discontinuous mode opera- tion, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. Choosing L greater than 3(VOUT + VD) μH prevents subharmonic oscillations at all duty cycles. Catch Diode A 0.5A or 1A Schottky diode is recommended for the catch diode, D1. The diode must have a reverse voltage rating equal to or greater than the maximum input voltage. The ON Semiconductor MBR0540 is a good choice; it is rated for 0.5A forward current and a maximum reverse voltage of 40V. The MBRM140 provides better efficiency, and will handle extended overload conditions. Input Capacitor Bypass the input of the LT1933 circuit with a 2.2μF or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and ap- plied voltage, and should not be used. A 2.2μF ceramic is adequate to bypass the LT1933 and will easily handle the ripple current. However, if the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input sup- ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT1933 and to force this very high frequency |
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