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LT3475 Datasheet(PDF) 10 Page - Linear Technology |
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LT3475 Datasheet(HTML) 10 Page - Linear Technology |
10 / 20 page LT3475/LT3475-1 10 3475fb current have significantly increased. Exceeding VIN(MAX) is safe if the external components have adequate ratings to handle the peak conditions and if the peak inductor current does not exceed 3.2A. A saturating inductor may further reduce performance. Table 2. Inductors PART NUMBER VALUE (μH) IRMS (A) DCR ( ) HEIGHT (mm) Sumida CR43-3R3 3.3 1.44 0.086 3.5 CR43-4R7 4.7 1.15 0.109 3.5 CDRH4D16-3R3 3.3 1.10 0.063 1.8 CDRH4D28-3R3 3.3 1.57 0.049 3.0 CDRH4D28-4R7 4.7 1.32 0.072 3.0 CDRH6D26-5R0 5.0 2.20 0.032 2.8 CDRH6D26-5R6 5.6 2.0 0.036 2.8 CDRH5D28-100 10 1.30 0.048 3.0 CDRH5D28-150 15 1.10 0.076 3.0 CDRH73-100 10 1.68 0.072 3.4 CDRH73-150 15 1.33 0.130 3.4 CDRH104R-150 15 3.1 0.050 4.0 Coilcraft DO1606T-332 3.3 1.30 0.100 2.0 DO1606T-472 4.7 1.10 0.120 2.0 DO1608C-332 3.3 2.00 0.080 2.9 DO1608C-472 4.7 1.50 0.090 2.9 MOS6020-332 3.3 1.80 0.046 2.0 MOS6020-472 10 1.50 0.050 2.0 DO3316P-103 10 3.9 0.038 5.2 DO3316P-153 15 3.1 0.046 5.2 The optimum inductor for a given application may differ from the one indicated by this simple design guide. A larger value inductor provides a higher maximum load current, and reduces the output voltage ripple. If your load is lower than the maximum load current, then you can relax the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCRresultinginhigherefficiency.Inaddition,lowinductance may result in discontinuous mode operation, which further reduces maximum load current. For details of maximum outputcurrentanddiscontinuousmodeoperation,seeLinear Technology’s Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), a minimum inductance is required to avoid sub-harmonic oscillations: LMIN = (VOUT + VF )• 800kHz f VSW 20V/DIV IL 1A/DIV VOUT 500mV/DIV (AC COUPLED) 3475 F04 Figure 4. Operation above VIN(MAX). Output Ripple and Peak Inductor Current Increases Inductor Selection and Maximum Output Current A good first choice for the inductor value is: L = (VOUT + VF )• 1.2MHz f where VF is the voltage drop of the catch diode (~0.4V), f is the switching frequency and L is in μH. With this value the maximum load current will be above 1.6A at all duty cycles. The inductor’s RMS current rating must be greater than the maximum load current and its saturation current should be at least 30% higher. For highest efficiency, the series resistance (DCR) should be less than 0.15Ω. Table 2 lists several vendors and types that are suitable. For robust operation at full load and high input voltages (VIN > 30V), use an inductor with a saturation current higher than 3.2A. APPLICATIONS INFORMATION |
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Similar Description - LT3475_15 |
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