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MP2188 Datasheet(PDF) 13 Page - Monolithic Power Systems |
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MP2188 Datasheet(HTML) 13 Page - Monolithic Power Systems |
13 / 17 page MP2188 – DUAL 3A, 5.5V, 1.2MHz, SYNCHRONOUS STEP-DOWN SWITCHER MP2188 Rev. 1.01 www.MonolithicPower.com 13 2/2/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The MP2188 output voltage of the two channels can be changed with external feedback resistors. The feedback resistors cannot be too large considering the internal divider resistors. Choose external feedback resistors <20kΩ: Using below formulas to set the new output voltages: R1_IN V V I CH OUT FB − = R _ ESD I 6 . 0 V FB FB × − = 2 2 FB FB FB OUT 1 R R I V V V R × × − − = Where, VCH is the pre-set fixed output voltage of each channel. For channel 1: VCH=1.1V, R1_IN =214.58kOhm, ESD_R=3.59kOhm. For channel 2: VCH=1.8V, R1_IN =227.61kOhm, ESD_R=4.28kOhm. To mask internal resistor well, the adjustable VOUT is recommended to set higher than 0.8V. Table 1 lists the recommended resistors values for common output voltage. Table 1: Resistor Values for Common Output Voltages 1.1V output channel 1.8V output channel VOUT(V) R1(kΩ) R2(kΩ) R3(kΩ) R4(kΩ) 1.2 3.01 3 3 3 1.5 4.7 3 4.3 3 1.8 6.34 3 6.2 3 2.5 10.5 3 10 3 3.3 15.4 3 14.7 3 Selecting the Inductor A 0.82µH to 4.7µH inductor is recommended for most applications. For highest efficiency, chose an inductor with a DC resistance less than 15mΩ. For most designs, the inductance value can be derived from the following equation. OSC L IN OUT IN OUT f I V ) V V ( V L × Δ × − × = Where ΔIL 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 Δ =+ 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, use 47μF 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: ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ × − × = IN OUT IN OUT LOAD CIN V V 1 V V I I The worse case condition occurs at VIN = 2VOUT, where: 2 I I LOAD CIN = For simplification, choose an input capacitor whose RMS current rating is greater than half of the maximum load current. |
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