TS19460_15 Datasheet, PDF (6/9 Pages) Taiwan Semiconductor Company, Ltd – AC/DC WLED Driver with Average-Mode Constant Current Control

TS19460
Taiwan Semiconductor
APPLICATION INFORMATION
The TS19460 is optimized to drive buck LED drivers using average current mode control. This method of control
enables fairly accurate LED current control without the need for high side current sensing or the design of any
closed loop controllers. The IC uses very few external components and enables both linear and PWM dimming of
the LED current.
A resistor connected to the RT pin programs the off-time. Constant off-time control average current mode is used
for stability and to improve the LED current regulation over a wide range of input voltages.
The current through the switching MOSFET source is averaged and used to give constant-current feedback. This
current is detected from a sense resistor at the CS pin, the feedback operates in a fast open-loop mode, there is no
compensation required, the output current is programmed as
I_LED = 0.25V / R_CS
When the Voltage at the LD input >1.5V, otherwise
I_LED = ( V_LD * 0.181 ) / R_CS
When application to design the inductor witching ripple current in it is 40% of average peak to peak, full load
current, the inductance can be calculated as follow:
L_OUT = ( V_OUT(max) * T_OFF ) / ( 0.4 * I_OUT )
The duty cycle range of current control feedback is limited to duty <75%, A reduction in the LED current string
voltage is greater than 75% of input voltage.
Reducing the output LED voltage is below V_OUT(MIN) = V_IN * D_(MIN), where D_(MIN) = 1uS / (T_OFF + 1uS), may also
result in the loss of regulation of LED current. This condition will cause an increase in the LED current and can be
possible to trip the short circuit protection comparator.
The short circuit protection comparator trips when the voltage at CS exceeds 0.44V, the Gate off time (T_HICCUP =
400μs) is generated to prevent stair-casing of inductor current and potentially its saturation due to insufficient
output voltage.
The leading edge blanking delay is provided at CS to prevent false triggering of current feedback and short circuit
protection.
Input Voltage Regulator
The TS19460 can be powered directly from its V_IN pin and can work from 8.0V_DC~450V_DC at its V_IN pin. When a
voltage is applied at the V_IN pin, the TS19460 maintains a constant 7.5V at the V_DD pin. This voltage is used to
power the IC and any external resistor dividers needed to control the IC. The V_DD pin must be bypassed by a low
ESR capacitor to provide a low impedance path for the high frequency current of the output GATE driver. The
TS19460 can be also operated by supplying a voltage at the V_DD pin greater than the internally regulated voltage.
Please note that this external voltage at the V_DD pin should not exceed 12V.
Although the V_IN pin of the TS19460 is rated up to 450V, the actual maximum voltage that can be applied is limited
by the power dissipation in the IC. For example, if an SOP-8 (junction to ambient thermal resistance Rθ_JA = 128°C/
W) TS19460 draws about I_IN = 2.0mA from the V_IN pin, and has a maximum allowable temperature rise of the
junction temperature limited to about the maximum voltage at the V_IN pin would be:
V_IN(MAX) = ( T_J(MAX) – T_A ) / ( Rθ_JA * I_IN ) = 390V
Document Number: DS_P0000188
6
Version: D15