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MP2187 датащи(PDF) 15 Page - Monolithic Power Systems |
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MP2187 датащи(HTML) 15 Page - Monolithic Power Systems |
15 / 18 page MP2187 – DUAL 3A, 5.5V, 1.2MHz, SYNCHRONOUS STEP-DOWN SWITCHER MP2187 Rev. 1.0 www.MonolithicPower.com 15 12/12/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 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 1 C V V 1 V V I I The worse case condition occurs at VIN = 2VOUT, where: 2 I I LOAD 1 C = 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 SIN IV V V1 fC1 V V ⎛⎞ Δ= × × − ⎜⎟ × ⎝⎠ Selecting the Output Capacitor The output capacitor (C2) maintains the output DC voltage. Use ceramic capacitors. Low-ESR capacitors keep the output voltage ripple low. The output voltage ripple can be estimated by: OUT OUT OUT ESR S1 IN S VV 1 V1 R fL V 8 f C2 ⎛⎞ ⎛⎞ Δ= × − × + ⎜⎟ ⎜⎟ ×× × ⎝⎠ ⎝⎠ Where L1 is the inductor value and RESR is the equivalent series resistance of the output capacitor. Using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated by: OUT OUT OUT 2 IN S1 VV ΔV1 V 8f L C2 ⎛⎞ =× − ⎜⎟ ×× × ⎝⎠ For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated as: OUT OUT OUT ESR IN S1 VV ΔV1 R fL V ⎛⎞ =× − × ⎜⎟ × ⎝⎠ The characteristics of the output capacitor also affect the stability of the regulation system. PCB Recommendation of MP2187 Proper layout of the switching power supplies is very important, and sometimes critical for proper operation. For high-frequency switching converters, poor layout could lead to poor line or load regulation and stability issues. The high current paths (GND, IN, and SW) should be placed very close to the device using short, direct, and wide traces. The input capacitor needs to be as close as possible to the IN and GND pins. The external feedback resistors should be placed next to the FB pin. Keep the switching node SW short and away from the feedback network. For MP2187 PCB layout, there are two recommended layouts for selecting. Figure 2 (refer to schematic figure 4) shows symmetric PCB layout. If the layout is space limited, and has to be asymmetric, a ferrite bead (The Impedance should >220mΩ@100MHz) is suggested to separate the two input of each channel. Figure 3 (refer to schematic figure 5) shows asymmetric PCB layout. Figure 2: Symmetric PCB Layout |
Аналогичный номер детали - MP2187 |
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Аналогичное описание - MP2187 |
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