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MP2145 Datasheet(PDF) 16 Page - Monolithic Power Systems |
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MP2145 Datasheet(HTML) 16 Page - Monolithic Power Systems |
16 / 19 page MP2145 – 5.5V, 6A, 1.2MHz, COT, BUCK SWITCHER MP2145 Rev. 1.11 www.MonolithicPower.com 16 12/20/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The external resistor divider sets the output voltage (see the Typical Application schematic). Select the feedback resistor R1 which considers reducing VOUT leakage current, typically between 40k Ω to 200kΩ. There is not strict requirement on feedback resistor. R1>10kΩ is reasoned for some application. R2 can be gotten below then: out R1 R2 V 1 0.6 The feedback circuit is shown as Figure 6: R1 R2 Vout FB MP2145 Figure 6: Feedback Network Table 1 lists the recommended resistors values for common output voltages. Table 1: Resistor Values for Common Output Voltages VOUT (V) R1 (k Ω) R2 (k Ω) 1.0 200(1%) 300(1%) 1.2 200(1%) 200(1%) 1.8 200(1%) 100(1%) 2.5 200(1%) 63.2(1%) 3.3 200(1%) 44.2(1%) Selecting the Inductor In order to achieve high efficiency at light load, a low value inductor such as 0.47 µH is recommended for most applications. For highest efficiency, chose an inductor with a DC resistance less than 30m Ω. For most designs, the inductance value can be derived from the following equation. OUT IN OUT 1 IN L OSC V (V V ) L V I f Where ΔI L is the inductor ripple current. Choose an inductor current to be approximately 30% of the maximum load current. The maximum inductor peak current is: L L(MAX) LOAD I II 2 Selecting the Input Capacitor The input current to the step-down converter is discontinuous, and requires a capacitor to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low-ESR capacitors for the best performance. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR values and small temperature coefficients. For most applications, a 22µF capacitor is sufficient. For higher output voltage, 47uF may be needed to improve system stability. Since the input capacitor absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: OUT OUT C1 LOAD IN IN VV I I 1 VV The worse case condition occurs at VIN = 2VOUT, where: LOAD C1 I I 2 For simplification, choose an input capacitor whose RMS current rating greater than half of the maximum load current. The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, use a small high-quality ceramic capacitor (0.1μF), placed as close to the IC as possible. When using ceramic capacitors, make sure that they have enough capacitance to prevent excessive voltage ripple at input. The input voltage ripple caused by capacitance can be estimated by: LOAD OUT OUT IN IN S IN I V V V1 f C1 V V |
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