TS19452 Datasheet, PDF (4/7 Pages) Taiwan Semiconductor Company, Ltd – AC/DC WLED Driver with Internal MOSFET

TS19452
AC/DC WLED Driver with Internal MOSFET
Universal Switch Mode
Application Information (Continue)
Where L is the inductance value, and C_L is the coil capacitance. Charging and discharging this capacitance every
switching cycle causes high-current spikes in the LED string. Therefore, connecting a small capacitor C_O(~100nF)
is recommended to bypass these spikes.
Using an ultra-fast rectifier diode for D1 is recommended to achieve high efficiency and reduce the risk of false
triggering of the current sense comparator. Using diodes with shorter reverse recovery time t_rr and lower junction
capacitance C_J achieves better performance. The reverse voltage rating V_R of the diode must be greater than the
maximum input voltage of LED lamps.
The total parasitic capacitance present at the Drain pin of the TS19452 can be calculated as:
C_P = C_DRAIN + C_PCB + CL + C_J
When the switching MOSFET turns on, the capacitance C_P is discharged into the Drain pin of the IC. The discharge
current is limited to about 150mA typically. However, it may become lower at increased junction temperature. The
duration of the leading edge current spike can be estimated as:
T_PSIKE = ((V_IN x C_P) / (I_SAT)) + t_r
EMI Filter
As with all off-line converters, selecting an input filter is critical to obtaining good EMI. A switching side capacitor,
albeit of small value, is necessary in order to ensure low impedance to the high frequency switching currents of the
converter. As a rule of thumb, this capacitor should be approximately 0.1~0.2µF/W of LED output power.
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Version: A12