TS19453CS-RLG datasheet(4/7 Pages) TSC

4 / 7 page

Preliminary

TS19453

AC/DC Programmable Current WLED Driver

w/PWM Dimming Control

4/7

Version: Preliminary

Application Information (Continue)

L is the inductance value, and CL 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 CO(~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 trr and lower junction

capacitance CJ achieves better performance. The reverse voltage rating VR 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 TS19453 can be calculated as:

CP = CDRAIN + CPCB + CL + CJ

When the switching MOSFET turns on, the capacitance CP is discharged into the Drain pin of the IC. The discharge

current is limited to about 50mA typically. However, it may become lower at increased junction temperature. The

duration of the leading edge current spike can be estimated as:

TPSIKE = ((VIN x CP) / (ISAT)) + trr

In order to avoid false trigger of the current sense comparator, CP must be minimized in accordance with the

following expression.

CP =< (Isat * ( TBLANK(min) - trr )) / Vin(max)

When TBLANK(min) is the minimum blanking time of 200nS, and Vin(max) is the maximum instantaneous input voltage.

Estimating Power Loss

Discharging the parasitic capacitance CP in the the Drain output of TS19453 is responsible for the bulk of the

switching power loss. It can be estimated using as:

PSWITCH = ((CP * VIN

2 / 2 ) + (V

IN * ISAT * trr)) * FS

FS is the switching frequency and is the saturated Drain current of TS19453, the switching loss is the greatest at

the maximum input voltage.

Disregarding the voltage drop at TS19453 and D1, the switching frequency is given as

FS = (VIN - VOUT ) / (VIN * TOFF)

When the TS19453 is powered from full wave rectified AC input, the swithching power loss can be estimated as:

PSWITCH = 1 / (2 * TOFF) * ((VAC * CP + 2 * ISAT * trr ) * (VAC - VOUT )))

When the TS19453 is powered from DC input voltage, conduction power loss can be estimated as:

PCOND = (D * IOUT

2 * R

ON) + IDD * VIN * (1 – D)

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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