Design and Implementation of On-board Electrical Power ... - OUFTI-1
Design and Implementation of On-board Electrical Power ... - OUFTI-1
Design and Implementation of On-board Electrical Power ... - OUFTI-1
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Switching frequencyThe switching frequency <strong>of</strong> the TPS63001 is between 1,250 <strong>and</strong> 1,500 kHz.<strong>Design</strong> <strong>of</strong> inductor <strong>and</strong> capacitorThe components <strong>of</strong> the 3.3V converter must suit for the two operation modes, buck <strong>and</strong> boost.Two worksheets were used, one for the design <strong>of</strong> the boost mode (it is the same worksheet asfor the other converters), <strong>and</strong> one for the design <strong>of</strong> the buck mode (it is a new worksheet).For the buck mode, the inductance is computed using Eq. 5.9. The peak inductor currentis found with Eq. 5.7. The desired series resistance <strong>and</strong> the output capacitor are alsodetermined with Eqs. 5.10 <strong>and</strong> 5.13.The inputs are V in,Min , V in,Max , V out , I out,Max , the expected efficiency η, the switchingfrequency f s , k (∆i L /I av max), <strong>and</strong> ∆v max .The V in,Min for the buck mode is equal to the V in,Max for the boost mode but it is notnecessarily 3.3V. For a buck converter with an efficiency <strong>of</strong> η, the V inMin is equal to Voutη .Similarly, for a boost converter with a efficiency <strong>of</strong> η, the V in,Max is equal to Voutη .Inductor selectionThe chosen inductor is the EPCOS B82472P6472M000. It is the same model as for the5V converter. The inductance is 4.7µH. With this value, the k is equal to 0.429 in the boostmode <strong>and</strong> equal to 0.633 in the buck mode. <strong>On</strong>ce again, the k is quite high but the converterworks fine with a high k (the recommended value for L in the datasheet is 2.2µH).Capacitor selection<strong>On</strong>e 10µF ceramic capacitor will be used at the output.The maximum inductor current is 0.34A. This current is acceptable for the switch, whichis able to withst<strong>and</strong> 1.6A.<strong>Design</strong> <strong>of</strong> other componentsC by <strong>and</strong> R byR by <strong>and</strong> C by are decoupling components. Values <strong>of</strong> respectively 100Ω <strong>and</strong> 0.1µF arerecommended by the datasheet <strong>of</strong> the TPS63001.Schottky diodeThe present 3.3V converter <strong>and</strong> the EPS2 [2] will have to work in parallel. The behavior<strong>of</strong> these system must be studied. The engineering model will be equipped <strong>of</strong> a Schottky diodeon the output <strong>of</strong> the 3.3V converter, before the feedback loop. A jumper will be placed inparallel to short-circuit the diode if needed. The same model <strong>of</strong> diode as in the 7.2V converteris used.67
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