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## FC9921 Datasheet(PDF) 5 Page - First Silicon Co., Ltd

 No. de Pieza. FC9921 Descripción 3-Pin Switch-Mode LED Lamp Driver IC Descarga 8 Pages Scroll/Zoom 100% Fabricante FS [First Silicon Co., Ltd] Página de inicio http://www.firstsilicon.co.kr/ Logo

## FC9921 Datasheet(HTML) 5 Page - First Silicon Co., Ltd

 5 / 8 page FC99212012. 10. 315/8Revision No : 0current is limited to about 150mA typically. However, itmay become lower at increased junction temperature. Theduration of the leading edge current spike can be estimatedas:TSPIKE = ((VIN • CP) / (ISAT)) +trr(4)In order to avoid false triggering of the current sensecomparator, CP must be minimized in accordance with thefollowing expression:CP < ISAT •(TBLANK(MIN) - trr )(5)VIN(MAX)where TBLANK(MIN) is the minimum blanking time of 200ns, andVIN(MAX) is the maximum instantaneous input voltage.Estimating Power LossDischarging the parasitic capacitance CP into the DRAIN pin ofthe FC9921 is responsible for the bulk of the switching powerloss. It can be estimated using the following equation:PSWITCH = [(VIN2• CP ) / 2 + VIN • ISAT • trr ] • FS(6)where FS is the switching frequency, ISAT is the saturatedDRAIN current of the FC9921. The switching loss is thegreatest at the maximum input voltage.The switching frequency is given by the following:FS = (VIN - η-1• VO) / VIN • TOFF(7)whereηWhen the FC9921 LED driver is powered from the full-waveas:PSWITCH ≈(8)1(VAC • CP + 2 • ISAT • trr )(VAC - η-1• VO )2 • TOFFVAC is the input AC line voltage.The switching power loss associated with turn-off transitionsof the DRAIN pin can be disregarded. Due to the large amountof parasitic capacitance connected to this switching node,the turn-off transition occurs essentially at zero-voltage.Conduction power loss in the FC9921 can be calculated as:PCOND = (D • IO2• RON) + [IDD • VIN • (1 - D)](9)where D = VO /ηVIN is the duty ratio, RON is the on-resistance,IDD is the internal linear regulator current.When the LED driver is powered from the full-waveconduction loss is more cumbersome. However, it can beestimated using the following equation:PCOND = (KC • IO2• RON ) + (KD • IDD • VAC )(10)where VACCand Kd can be determined from the minimum duty ratio ofthe FC9921.Fig. 1.C and KdEMI FilterAs wto obtaining good EMI. A switching side capacitor, albeit ofsmall value, is necessary in order to ensure low impedanceto the high frequency switching currents of the converter. Asa rule of thumb, this capacitor should be approximately 0.1-shown in Figure 2 for the following design example.Design ExampleLet us design an FC9921 LED lamp driver meeting theInput:Universal AC, 85-265VACOutput Current: 20mALoad:String of 10 LED (LW541C by OSRAMVF = 4.1V max. each)00.10.20.30.40 50.60.70.70.60.50.40.30.20.1Kd(Dm)Kc(Dm)Dm