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LTM4661 Fiches technique(PDF) 8 Page - Linear Technology |
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LTM4661 Fiches technique(HTML) 8 Page - Linear Technology |
8 / 20 page LTM4661 8 4661f For more information www.linear.com/LTM4661 The typical LTM4661 application circuit is shown in Figure 17. External component selection is primarily de- termined by the input voltage, the output voltage and the maximum load current. Minimum Input Voltage The LTM4661 is designed to allow start-up from input voltages as low as 1.8V. When VOUT exceeds 2.5V, the LTM4661 continues to regulate its output, even when VIN falls as low as 0.7V. This feature extends operating times by maximizing the amount of energy that can be extracted from the input source. The limiting factors for the applica- tion become the availability of the power source to supply sufficient power to the output at the low input voltage, and the maximum duty cycle, which is clamped at 94%. In a step-up boost converter, the duty cycle can be cal- culated at: D = 1– VIN • η VOUT where ηistheconverterefficiency.85%isagoodestimate to start with. Note that at low input voltages, voltage drops due to series resistance become critical and greatly limit the power delivery capability of the converter. Output Current Capability The LTM4661 is designed to provide up to 4A switch cur- rent. Due to the nature of the boost converter, the actually output current capability depends highly on the input/ output voltage ratio. The peak inductor current, same as switch current, in a boost converter can be calculated as: ISW = VIN • D 2 • fS • L + IOUT 1– D where D is the duty cycle showing above and fS = 1MHz and L = 2.2µH/2 = 1.1µH. APPLICATIONS INFORMATION Based on common input and output values, Table 1 lists differentoutputcurrentcapabilityoftheLTM4661module. Table 1. Output Current Capability vs Input Voltage VIN (V) 3.3 5 VOUT (V) 5 8 12 15 8 12 15 Output Current (A) 1.9 1 0.7 0.5 1.7 1 0.7 Efficiency (%) 82 84 83 81 88 87 88 Peak Switch Current (A) 4 3.8 3.9 4 3.94 4.1 4.1 Output Voltage Programming The PWM controller has an internal 1.2V reference volt- age. As shown in the Block Diagram, a 100k 0.5% internal feedback resistor connects VOUT and FB pins together. Adding a resistor RFB from FB pin to GND, programs the output voltage: RFB = 1.2V VOUT – 1.2V • 100k Table 2. VFB Resistor Value vs Various Output Voltages VOUT (V) 1.2 2.5 3.3 5 8 12 15 RFB (k) OPEN 93.1 57.6 31.6 17.8 11.0 8.66 For parallel operation of N-piece of LTM4661 modules, the following equation can be used to solve for RFB: RFB = 1.2V VOUT – 1.2V • 100k N Multiphase Operation The LTM4661 uses a unique dual-phase single-output architecture, rather than the conventional single phase of otherboostconverters.Byinterleavingtwophasesequally spaced 180° apart, both input and output current ripple get significantly reduced as well as the amount of input and output decoupling capacitor required. |
Numéro de pièce similaire - LTM4661 |
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Description similaire - LTM4661 |
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