TS19460CSRLG datasheet(6/9 Pages) TSC

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TS19460

Taiwan Semiconductor

Document Number: DS_P0000188

Version: D15

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

ILED = 0.25V / RCS

When the Voltage at the LD input >1.5V, otherwise

ILED = ( VLD * 0.181 ) / RCS

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:

LOUT = ( VOUT(max) * TOFF ) / ( 0.4 * IOUT )

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

VOUT(MIN) = VIN * D(MIN), where D(MIN) = 1uS / (TOFF + 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 (

THICCUP =

400

μs) 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 VIN pin and can work from 8.0VDC~450VDC at its VIN pin. When a

voltage is applied at the VIN pin, the TS19460 maintains a constant 7.5V at the VDD pin. This voltage is used to

power the IC and any external resistor dividers needed to control the IC. The VDD 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 VDD pin greater than the internally regulated voltage.

Please note that this external voltage at the VDD pin should not exceed 12V.

Although the VIN 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 IIN = 2.0mA from the VIN pin, and has a maximum allowable temperature rise of the

junction temperature limited to about the maximum voltage at the VIN pin would be:

VIN(MAX) = ( TJ(MAX) – TA ) / ( RθJA * IIN ) = 390V

TS19460CSRLG Datasheet(PDF) 6 Page - Taiwan Semiconductor Company, Ltd

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