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AAT1154IAS-1.0-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT1154IAS-1.0-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
10 / 16 page AAT1154 1MHz 3A Step-Down DC/DC Converter 10 1154.2006.09.1.6 Inductor The output inductor is selected to limit the ripple current to 20% to 40% of full load current at the maximum input voltage. Manufacturer's specifica- tions list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the inductor saturation characteristics. The inductor should not show any appreciable saturation under normal load condi- tions. During overload and short-circuit conditions, the inductor can exceed its peak current rating without affecting converter performance. Some inductors may have sufficient peak and average current ratings yet result in excessive losses due to a high DC resistance (DCR). The losses associat- ed with the DCR and its effect on the total convert- er efficiency must be considered. For a 3A load and the ripple current set to 30% at the maximum input voltage, the maximum peak-to-peak ripple current is 0.9A. Assuming a 5V ±5% input volt- age and 30% ripple, the output inductance required is: The factor "k" is the fraction of the full load (30%) selected for the ripple current at the maximum input voltage. The corresponding inductor RMS current is: ΔI is the peak-to-peak ripple current which is fixed by the inductor selection above. For a peak-to-peak current of 30% of the full load current, the peak cur- rent at full load will be 115% of the full load. The 1.5µH inductor selected from the Sumida CDRH6D38 series has a 11m Ω DCR and a 4.0A DC current rating with a height of 4mm. At full load, the inductor DC loss is 99mW for a 1% loss in efficiency. 2 2 3 12 RMS O O I II I A ⎛⎞ Δ =+ = ⎝⎠ ≈ L = · 1 - V OUT V OUT I OUT · k · FS V IN(MAX) = · 1 - 3.3V 3.3V 3A · 0.3 · 1MHz 5.25V ⎛⎞ ⎝⎠ ⎛⎞ ⎛ ⎞ ⎝⎠ ⎝ ⎠ = 1.36 μH Figure 1: 3.3V, 3A Output. D1 B340LA L1 1.5µH C2 120µF C1 10µF VP VCC EN GND FB LX LX VP U1 AAT1154-3.3 R1 100 C3 0.1µF C3 0.1µF 0603ZD104M AVX L1 CDRH6D28-1.5µH Sumida D1 B340LA Diodes Inc. R2 100k C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3 C2 MuRata 100µF 6.3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel) VIN 3.5V to 5.5V VOUT 3.3V @ 3A rtn C4 100µF C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V C2 Vishay120µF 6.3V 594D127X96R6R3C2T Options C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel) + - |
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