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MAX16831 Datasheet(PDF) 14 Page - Maxim Integrated Products |
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MAX16831 Datasheet(HTML) 14 Page - Maxim Integrated Products |
14 / 19 page Applications Information Inductor Selection The minimum required inductance is a function of oper- ating frequency, input-to-output voltage differential, and the peak-to-peak inductor current ( ΔIL). Higher ΔIL allows for a lower inductor value while a lower ΔIL requires a higher inductor value. A lower inductor value minimizes size and cost, improves large-signal tran- sient response but reduces efficiency due to higher peak currents and higher peak-to-peak output ripple voltage for the same output capacitance. On the other hand, higher inductance increases efficiency by reduc- ing the ripple current, ΔIL. However, resistive losses due to extra turns can exceed the benefit gained from lower ripple current levels, especially when the induc- tance is increased without also allowing for larger inductor dimensions. A good compromise is to choose ΔIL equal to 30% of the full load current. The inductor saturating current is also important to avoid runaway current during the output overload and continuous short circuit. Select the ISAT to be higher than the maxi- mum peak current limit. Buck configuration: In a buck configuration, the aver- age inductor current does not vary with the input. The worst-case peak current occurs at a high input voltage. In this case, the inductance L for continuous conduc- tion mode is given by: where VINMAX is the maximum input voltage, fSW is the switching frequency, and VOUT is the output voltage. Boost configuration: In the boost converter, the average inductor current varies with line and the maximum aver- age current occurs at low line. For the boost converter, the average inductor current is equal to the input cur- rent. In this case, the inductance L is calculated as: where VINMIN is the minimum input voltage, VOUT is the output voltage, and fSW is the switching frequency. Buck-boost configuration: In a buck-boost converter, the average inductor current is equal to the sum of the input current and the load current. In this case, the inductance L is: where VINMIN is the minimum input voltage, VOUT is the output voltage, and fSW is the switching frequency. Output Capacitor The function of the output capacitor is to reduce the output ripple to acceptable levels. The ESR, ESL, and the bulk capacitance of the output capacitor contribute to the output ripple. In most of the applications, the out- put ESR and ESL effects can be dramatically reduced by using low-ESR ceramic capacitors. To reduce the ESL effects, connect multiple ceramic capacitors in parallel to achieve the required bulk capacitance. In a buck configuration, the output capacitance, CF, is calculated using the following equation: where ΔVR is the maximum allowable output ripple. In a boost configuration, the output capacitance, CF, is calculated as: where IOUT is the output current. In a buck-boost configuration, the output capacitance, CF, is calculated as: where VOUT is the voltage across the load and IOUT is the output current. Connect the output capacitor(s) from the output to ground in a buck-boost configuration (not across the load as for other configurations). Input Capacitor A capacitor connected between the input line and ground must be used when configuring the MAX16831 as a buck converter. Use a low-ESR input capacitor that can handle the maximum input RMS ripple current. Calculate the maximum allowable RMS ripple using the following equation: In most of the cases, an additional electrolytic capaci- tor should be added to prevent input oscillations due to line impedances. I IV V V V IN RMS OUT OUT INMIN OUT INMIN () () = ×× - C VI VV V f F OUT OUT ROUT INMIN SW ≥ ×× ×+ × 2 Δ () C VV I VV f F OUT INMIN OUT ROUT SW ≥ ×× ×× () -2 Δ C VV V VL V f F INMAX OUT OUT RINMAX SW ≥ × ×× × × () - Δ 2 2 L VV VV f I OUT INMIN OUT INMIN SW L = × +× × () Δ L VV V Vf I INMIN OUT INMIN OUT SW L = × ×× () - Δ L VV V Vf I OUT INMAX OUT INMAX SW L = × ×× () - Δ High-Voltage, High-Power LED Driver with Analog and PWM Dimming Control 14 ______________________________________________________________________________________ |
Similar Part No. - MAX16831_09 |
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Similar Description - MAX16831_09 |
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