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CN5815 Datasheet(PDF) 10 Page - Shanghai Consonance Electronics Incorporated

 Part No. CN5815 Description 4.5V to 32V Input, Constant Current Boost HB LED Driver Download 12 Pages Scroll/Zoom 100% Maker CONSONANCE [Shanghai Consonance Electronics Incorporated] Homepage http://www.consonance-elec.com/ Logo

CN5815 Datasheet(HTML) 10 Page - Shanghai Consonance Electronics Incorporated

 10 / 12 page CONSONANCEwww.consonance-elec.com10REV 1.0The inductor, output capacitor and the load RLED form 1 pole and 2 zeros, they are:The pole formed by output capacitor and the load:The zero formed by the output capacitor and its equivalent series resistance(ESR)This zero can be neglected if low ESR ceramic capacitor is used.A right half plane zero at the frequency:In the above 3 equations, VLED is the LED forward voltage, ILED is the LED current, COUT is the outputcapacitance, resr is the ESR of output capacitor, D is the duty cycle, and L is the inductance.In Figure 2, C1, C2 and R3 form the compensation network. The design procedure of the compensation networkis:Step 1: Calculate ωP1, ωz1 and ωz2 based on the above 3 equationsStep 2: Determine the crossover frequency ωc of the overall loopFor stable operation, the overall loop gain should cross 0dB with -20dB/decade slope. Due to thepresence of the RHP zero, the 0dB crossover frequency should be from 0.3×ωz2 to 0.4×ωz2.Step 3: Determine R3’s value in ohm (Ω)Step 4: Calculate C1’s value in Farad (F)Step 5: Determine C2’s value in Farad (F)R3 and C2 form a pole used to cancel the effect of ωz1. If low ESR capacitor is used for output capacitor,ωz1 can be neglected, hence C2 can be omitted. Otherwise, C2 can be calculated by the equation:About Capacitor C5In the typical application circuit shown in Figure 1, capacitor C5 is used to filter out the high frequency noise sothat the over voltage protection can function correctly. Capacitor C5 is estimated by the below equation: