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LM3481-Q1 Datasheet(PDF) 22 Page - Texas Instruments |
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LM3481-Q1 Datasheet(HTML) 22 Page - Texas Instruments |
22 / 38 page ![]() DR VOUT FB L D1 Q ISEN COUT RF2 VIN LM3481 RSEN RF1 + RSEN = VSENSE - (D x VSL) IOUT(max) (1-D) + (D x VIN) (2 x fS x L) Isw(peak) = IOUT(max) (1-D) + (D x VIN) (2 x fS x L) VOUT = 1.275 (1+ RF1 RF2 ) LM3481, LM3481-Q1 SNVS346F – NOVEMBER 2007 – REVISED NOVEMBER 2014 www.ti.com Typical Applications (continued) A core size with ratings higher than these values should be chosen. If the core is not properly rated, saturation will dramatically reduce overall efficiency. The LM3481 can be set to switch at very high frequencies. When the switching frequency is high, the converter can operate with very small inductor values. With a small inductor value, the peak inductor current can be extremely higher than the output currents, especially under light load conditions. The LM3481 senses the peak current through the switch. The peak current through the switch is the same as the peak current calculated above. 8.2.1.2.2 Programming the Output Voltage and Output Current The output voltage can be programmed using a resistor divider between the output and the feedback pins, as shown in Figure 33. The resistors are selected such that the voltage at the feedback pin is 1.275 V. RF1 and RF2 can be selected using the equation, (28) A 100-pF capacitor may be connected between the feedback and ground pins to reduce noise. The maximum amount of current that can be delivered at the output can be controlled by the sense resistor, RSEN. Current limit occurs when the voltage that is generated across the sense resistor equals the current sense threshold voltage, VSENSE. Limits for VSENSE have been specified in the Electrical Characteristics section. This can be expressed as: Isw(peak) x RSEN = VSENSE- D x VSL (29) The peak current through the switch is equal to the peak inductor current. Isw(peak) = IL(max) + ΔiL (30) Therefore for a boost converter, (31) Combining the two equations yields an expression for RSEN, (32) Evaluate RSEN at the maximum and minimum VIN values and choose the smallest RSEN calculated. Figure 33. Adjusting the Output Voltage 22 Submit Documentation Feedback Copyright © 2007–2014, Texas Instruments Incorporated Product Folder Links: LM3481 LM3481-Q1 |
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