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MP2225 数据表(PDF) 14 Page - Monolithic Power Systems |
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MP2225 数据表(HTML) 14 Page - Monolithic Power Systems |
14 / 20 page MP2225 –18V/5A SYNCHRONOUS STEP-DOWN CONVERTER MP2225 Rev. 1.01 www.MonolithicPower.com 14 4/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. APPLICATION INFORMATION Setting the Output Voltage The external resistor divider sets the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. First, choose a value for R1, R2 is then given by: OUT R1 R2 V 1 0.6V = − (1) The feedback network—as shown in Figure 5— is highly recommended. Figure 5: Feedback Network Table 1 lists the recommended resistors and capacitors value for common output voltages. Table 1: Component Selection for Common Output Voltages (9) VOUT (V) R1 (kΩ) R2 (kΩ) 1.0 120 180 1.2 120 120 1.35 100 80.6 1.5 80.6 53.6 1.8 80.6 40.2 2.5 80.6 25.5 3.3 40.2 8.87 5 40.2 5.49 9) The recommended parameters are based on 500kHz switching frequency, different output inductors and capacitors affect the recommended values of R1 and R2. For the other components’ parameters, please refer to TYPICAL APPLICATION CIRCUITS on 17-19. Selecting the Inductor Use a 1µH-to-10µH inductor with a DC current rating at least 25% percent higher than the maximum load current for most applications. For highest efficiency, use an inductor with a DC resistance less than 15mΩ. For most designs, the inductance value can be derived from the following equation. OUT IN OUT 1 IN L OSC V(V V ) L VI f × − = ×Δ × (2) Where ΔIL is the inductor ripple current. Choose the inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current is: 2 I I I L LOAD ) MAX ( L Δ + = (3) Use a larger inductor for improved efficiency under light-load conditions—below 100mA. Selecting the Input Capacitor The input current to the step-down converter is discontinuous, therefore 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. Use ceramic capacitors with X5R or X7R dielectrics for best results because of their low ESR and small temperature coefficients. For most applications, use a 22µF capacitor. Since C1 absorbs the input switching current, it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ × − × = IN OUT IN OUT LOAD 1 C V V 1 V V I I (4) The worse case condition occurs at VIN = 2VOUT, where: 2 I I LOAD 1 C = (5) For simplification, choose an input capacitor with an 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, add a small, high quality ceramic capacitor (e.g. 0.1μF) placed as close to the IC |
类似零件编号 - MP2225 |
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类似说明 - MP2225 |
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