TS19460CSRLG datasheet(7/9 Pages) TSC

7 / 9 page

TS19460

Taiwan Semiconductor

Document Number: DS_P0000188

Version: D15

APPLICATION INFORMATION (CONTINUE)

In these cases, to operate the TS19460 from higher input voltages, a Zener diode can be added in series with the

VIN pin to divert some of the power loss from the TS19460 to the Zener diode. In the above example, using a 100V

Zener diode will allow the circuit to easily work up to 490V.

The input current drawn from the VIN pin is a sum of the 1.0mA current drawn by the internal circuit and the current

drawn by the GATE driver (which in turn depends on the switching frequency and the GATE charge of the external.

IIN ≈ 1mA + QG x fS

In the above equation, fS is the switching frequency and QG is the GATE charge of the external MOSFET (which

can be obtained from the datasheet of the MOSFET).

Oscillator

The oscillator in the TS19460 is controlled by a single resistor connected at the RT pin. The equation governing the

off-time of the GATE output is given by:

TOFF(μS) = ( RT(kΩ) / 25 ) + 0.3

within the range of 30kΩ ≤ R

T ≤ 1MΩ

Linear Dimming

The Linear Dimming pin is used to control the LED current, when voltage at LD is fall below 1.5V, the internal

reference voltage (250mV) to the constant current feedback become over ridden by VLD * 0.181, and the current in

the inductor remain continuous, the LED current is given by ILED = ( VLD * 0.181 ) / RCS, The Gate output is disable

when LD voltage <150mV(typ.) and recovery when LD voltage >200mV (typ.)

The Linear Dimming input could also be used for mixed-mode dimming to expand the dimming ratio, in this kind of

application condition, the pulse-width modulated signal of a measured amplitude below 1.5V should be applied at

LD.

PWM Dimming

PWM Dimming can be achieved by driving the PWMD pin with a square wave signal. The rising and falling edges

are limited by current slew rate in inductor, the first switching cycle is terminated upon reaching the level (250mV)

at CS, the circuit is further reaching its steady state within 3~5 switching cycle regardless of the switching

frequency.

TS19460CSRLG датащи(PDF) 7 Page - Taiwan Semiconductor Company, Ltd