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SE1484-HF Datasheet(PDF) 5 Page - Seaward Electronics Inc. |
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SE1484-HF Datasheet(HTML) 5 Page - Seaward Electronics Inc. |
5 / 8 page Rev1.0 Preliminary and all contents are subject to change without prior notice. © Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 5 9/4/2012 SE1484 3A 27V Synchronous Buck Converter Applications inductance value。 L based on the ripple current requirement: Where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE =~ 30% to correspond to the peak-to-peak ripple current being ~30% of the maximum output current. With this inductor value, the peak inductor current is IOUT•(1+KRIPPLE/2). Make sure that this peak inductor current is less than the upper switch current limit. Finally, select the inductor core size so that it does not saturate at the current limit. Typical inductor values for various output voltages are shown in Table 2. Table 2. Typical Inductor Values Output Voltage Setting Figure1. Output Voltage Setting Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors R1 and R2 based on the output voltage. Typically, use R2≈ 10KΩ and determine R1 from the following equation: Table1-Recommended Resistance Values: VOUT 1V 1.2V 1.8V 2.5V 3.3V 5V 9V L(uH) 4.7 4.7 10 10 10 10 22 VOUT R1 R2 Input Capacitor The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. A low ESR Electrolytic (EC) capacitor is highly recommended. Since large current flows in and out of this capacitor during switching, its ESR also affects efficiency. When EC cap is used, the input capacitance needs to be equal to or higher than 68uF. The RMS ripple current rating needs to be higher than 50% of the output current. The input capacitor should be placed close to the VIN and GND pins of the IC, with the shortest traces possible. The input capacitor can be placed a little bit away if a small parallel 0.1uF ceramic capacitor is placed right next to the IC. When Vin is >15V, pure ceramic Cin (* no EC cap) is not recommended. This is because the ESR of a ceramic cap is often too small, Pure ceramic Cin will work 1V 1.0K Ω 12K Ω 1.2V 3.0K Ω 10K Ω 1.8V 9.53K Ω 10K Ω 2.5V 16.9K Ω 10K Ω 3.3V 26.1K Ω 10K Ω 5V 44.2K Ω 10K Ω 12V 121K Ω 10K Ω Inductor Selection The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an |
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