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MP2560 Datasheet(PDF) 10 Page - Monolithic Power Systems |
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MP2560 Datasheet(HTML) 10 Page - Monolithic Power Systems |
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10 / 19 page 
MP2560 – 2.5A, 4MHz, 42V STEP-DOWN CONVERTER MP2560 Rev. 1.2 www.MonolithicPower.com 10 1/25/2010 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2010 MPS. All Rights Reserved. APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to FB pin. The voltage divider divides the output voltage down to the feedback voltage by the ratio: 2 R 1 R 2 R V V OUT FB + = Thus the output voltage is: 2 R ) 2 R 1 R ( V V FB OUT + = About 20µA current from high side BS circuitry can be seen at the output when the MP2560is at no load. In order to absorb this small amount of current, keep R2 under 40KΩ. A typical value for R2 can be 40.2kΩ. With this value, R1 can be determined by: ) k )( 8 . 0 V ( 25 . 50 1 R OUT Ω − × = For example, for a 3.3V output voltage, R2 is 40.2kΩ, and R1 is 124kΩ. Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage. However, the larger value inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. Also, make sure that the peak inductor current is below the maximum switch current limit. The inductance value can be calculated by: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − × × = IN OUT L S OUT V V 1 ∆I f V 1 L Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ∆IL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − × × × + = IN OUT S OUT LOAD LP V V 1 1 L f 2 V I I Where ILOAD is the load current. Table 1 lists a number of suitable inductors from various manufacturers. The choice of which style inductor to use mainly depends on the price vs. size requirements, the switching frequency, and any EMI requirement. |
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