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MP2229 Folha de dados(PDF) 15 Page - Monolithic Power Systems |
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MP2229 Folha de dados(HTML) 15 Page - Monolithic Power Systems |
15 / 22 page MP2229 – 21V, 6A SYNCHRONOUS STEP-DOWN CONVERTER MP2229 Rev. 1.0 www.MonolithicPower.com 15 2/12/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The external resistor divider sets the output voltage (see “Typical Application” on page 1). Choose R1 around 20kΩ, then R2 is: OUT R1 R2 V 1 0.6V = − The T-type network is recommended highly (see Figure 6). FIGURE 6. T-Type Network Table 1 lists the recommended T-type resistor values for common output voltages. TABLE1. Resistor Selection for Common Output Voltages (9) VOUT (V) R1 (kΩ) R2 (kΩ) RT (kΩ) 1.0 20 30 68 1.2 20 20 68 1.5 20 13.7 51 1.8 20 10 51 2.5 20 6.34 33 3.3 20 4.42 24 5 20 2.7 16 Notes: 9) The recommended parameters are based on a 500kHz switching frequency. A different input voltage, output inductors, and output capacitors may affect the recommended values of R1, R2, and RT. For additional component parameters, please refer to the “Typical Application Circuits” on pages 19-21. Selecting the Inductor For most applications, use a 1µH to 10µH inductor with a DC current rating at least 25% percent higher than the maximum load current. Select an inductor with a DC resistance less than 15mΩ for best efficiency. Use the following equation to derive the inductor value for most designs: OUT IN OUT 1 IN L OSC V(V V ) L VI f ×− = ×Δ × 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 + = Under light-load conditions (below 100mA), use a larger inductor for improved efficiency. Setting the Switching Frequency An external resistor (RFREQ) from FREQ/SYNC to GND sets the MP2229 oscillating frequency. The value of RFREQ can be calculated approximately using the formula below: FREQ S 16000 R(k ) -2.3 f(kHz) Ω= Setting the LPM Voltage The LPM voltage is used to set the transition point from LPM to CCM. Choose a transition point that provides the best combination of efficiency, stability, ripple, and transient. If the LPM voltage is set lower than the recommended value (see Figure 8), then stability and ripple improves but efficiency during LPM mode and transient degrades. Likewise, if the LPM voltage is set higher, then the efficiency during LPM and transient improves, but stability and ripple degrades. Calculate the optimal balance point of the LPM voltage for good efficiency, stability, and ripple. The LPM voltage comes from the tap of a resistor divider from VCC (5V) to GND (see Figure 7. FIGURE 7. LPM Network |
Nº de peça semelhante - MP2229 |
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Descrição semelhante - MP2229 |
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