TS19460_15 Datasheet, PDF (7/9 Pages) Taiwan Semiconductor Company, Ltd – AC/DC WLED Driver with Average-Mode Constant Current Control

TS19460
Taiwan Semiconductor
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 V_IN 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.
I_IN ≈ 1mA + Q_G x f_S
In the above equation, f_S is the switching frequency and Q_G 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:
T_OFF(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 V_LD * 0.181, and the current in
the inductor remain continuous, the LED current is given by I_LED = ( V_LD * 0.181 ) / R_CS, 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.
Document Number: DS_P0000188
7
Version: D15