MIC4827 Low Input Voltage, 180VPP Output Voltage, EL Driver - Micrel - #9

Text version of the page

Micrel, Inc. MIC4827 July 2009 9 M9999-070709-A (408) 955-1690 Application Information Inductor In general, smaller value inductors, which can handle more current, are more suitable to drive larger size lamps. As the inductor value decreases, the switching frequency (controlled by RSW) should be increased to avoid saturation or the input voltage should be increased. Typically, inductor values ranging from 220ìH to 560ìH can be used. Murata offers the LQH3C series up to 560ìH and LQH4C series up to 470ìH, with low DC resistance. A 220ìH Murata (LQH4C221K04) inductor is recommended for driving a lamp size of 3 square inches. It has a maximum DC resistance of 4.0Ù Diode The diode must have a high reverse voltage (150V), since the output voltage at the CS pin can reach up to 110V. A fast switching diode with lower forward voltage and higher reverse voltage (150V), such as BAV20WS, can be used to enhance efficiency. Output Capacitor Low ESR capacitors should be used at the regulated boost output (CS pin) of the MIC4827 to minimize the switching output ripple voltage. Selection of the capacitor value will depend upon the peak inductor current, inductor size, and the load. MuRata offers the GRM42-6 series with up to 0.047ìF at 100V, with a X7R temperature coefficient in 1206 surface-mount package. Typically, values ranging from 0.01ìF to 0.1ìF at 100V can be used for the regulated boost output capacitor Pre-designed Application Circuit R1332kR23.32MLi-Ion BatteryVIN3.0V to 4.2VC10.22..F/10VMurataGRM39X7R 224K10COUT0.01..F/100VGRM40X7R103KD1BAV20WSL1220..HMurataLQH4C221K0415687234SWCSVAVBVDDRSWRELGNDMIC48273in2 LAMPC210..F/6.3VMurataGRM42-6X5R106K6.3 VIN IIN VA – VB FEL Lamp Size 3.3V 28mA 180VPP 106Hz 3in2 TIME (2ms/div)VB(50V/div)VA(50V/div)VAÐVB(50V/div) Figure 5. Typical 100Hz EL Driver for 3in2 Lamp