| 전자부품 데이터시트 검색엔진 |
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LED7707 데이터시트(PDF) 35 Page - STMicroelectronics |
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LED7707 데이터시트(HTML) 35 Page - STMicroelectronics |
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35 / 48 page ![]() LED7707 Application information 35/48 TOFF can be calculated as: Equation 35 defining D2 as: Equation 36 The worst case for the output voltage ripple is when input voltage is lower (VIN,min = 10.8 V). A simple way to select the COUT value is fixing a maximum voltage ripple. In order to affect as less as possible the current generators, it would be better to fix the maximum ripple lower than the typical voltage across the generators. For example considering ΔV OUT lower than 70 mV (i.e. the 10 % of the voltage across the leading generator), the required capacitance is: Equation 37 A margin from the calculated value should be taken into account because of the capacitance drop due to the applied voltage when MLCCs are used. One 10 µF MLCC (or two 4.7 µF MLCCs) can be a good choice for this application. In case a dimming duty cycle different from 100% is used, a further contribution to the capacitor discharge (during the off time of the dimming cycle) should be considered. 6.4.5 Input capacitor choice The input capacitor of a boost converter is less critical than the output capacitor, due to the fact that the inductor is in series with the input, and hence, the input current waveform is continuous. A low ESR capacitor is always recommended. A capacitor of 10 µF is tentatively a good choice for most of the applications. ⎩ ⎨ ⎧ = = = ⋅ = V 2 . 13 V @ ns 2 . 618 V 8 . 10 V @ ns 7 . 569 D T T max , IN min , IN 2 SW OFF () ⎩⎨ ⎧ = = = − ⋅ ⋅ ⋅ ⋅ = V 2 . 13 V @ 408 . 0 V 8 . 10 V @ 376 . 0 1 M R M L F 2 D max , IN min , IN 0 SW 2 ( ) F 33 . 6 V 2 T I I C max , OUT OFF OUT peak , L OUT μ = Δ ⋅ ⋅ − > |
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