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MP2166 Datasheet(PDF) 16 Page - Monolithic Power Systems |
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MP2166 Datasheet(HTML) 16 Page - Monolithic Power Systems |
16 / 21 page MP2166 – 6V, DUAL 2A/2A OR 3A/1A, SYNC, BUCK REGULATOR WITH PG AND SS MP2166 Rev. 1.0 www.MonolithicPower.com 16 3/14/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. APPLICATION INFORMATION Setting the Output Voltage The external resistor divider sets the output voltage. The feedback resistor (R1) also sets the feedback loop bandwidth with the internal compensation (see Figure 5). FB VOUT R1 R2 Figure 5: External Resistor Divider In the case of ceramic capacitors used as output capacitors (CO), the feedback loop bandwidth (fC) is no higher than 1/10 of the switching frequency for optimal transient performance and good phase margin. If an electrolytic capacitor is used, the loop bandwidth is no higher than 1/4 of the ESR zero frequency (fESR). fESR can be calculated by Equation (2): ESR ESR O 1 f 2 R C (2) For example, choose fC = 80kHz with a ceramic capacitor and CO = 22μF. R1 is estimated to be 10 0kΩ. R2 can then be calculated with Equation (3): OUT R1 R2 V 1 0.6V (3) Use Table 1 to select resistor values based on different output voltages. Table 1: Resistor Selection vs. Output Voltage Setting VOUT R1 R2 1.2V 100k Ω 100k Ω 1.5V 100k Ω 66.5k Ω 1.8V 100k Ω 49.9k Ω 2.5V 100k Ω 31.6k Ω 3.3V 100k Ω 22.1k Ω Inductor Selection An inductor with a DC current rating at least 25% higher than the maximum load current is recommended for most applications. For best efficiency, the inductor DC resistance should be less than 20mΩ. For most designs, the inductance value can be derived from Equation (4): SW L IN OUT IN OUT f I V ) V - (V V L (4) Where ∆IL is inductor ripple current. Choose the inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current can be calculated with Equation (5): L L(MAX) LOAD ΔI I = I + 2 (5) Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high- frequency switching current from passing to the input source. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a 22µF capacitor is sufficient. Output Capacitor Selection The output capacitor (CO) keeps the output voltage ripple small and ensures a stable regulation loop. The output capacitor impedance should be low at the switching frequency. Use ceramic capacitors with X5R or X7R dielectrics. If an electrolytic capacitor is used, pay close attention to the output ripple voltage, extra heating, and the selection of the upper feedback resistor due to the large ESR of electrolytic capacitor (refer to the Setting the Output Voltage section). The output ripple ( ∆V OUT) can be approximated with Equation (6): ) 8 1 ( Co f ESR f L V ) V - (V V V SW SW IN OUT IN OUT OUT (6) |
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