TL4242,pdf(Adjustable LED Driv

The TL4242 is an integrated adjustable constant-current source, driving loads up to 500 mA. The output current level can be adjusted via an external resistor. The device is designed to supply high-power LEDs (for example, OSRAM Dragon LA W57B) under the severe conditions of automotive applications, resulting in constant brightness and extended LED lifetime. It is provided in the DRJ (QFN) package. Protection circuits prevent damage to the device in case of overload, short circuit, reverse polarity, and overheat. The connected LEDs are protected against reverse polarity as well as excess voltages up to 45 V.

The integrated PWM input of the TL4242 permits LED brightness regulation by pulse-width modulation (PWM). Due to the high input impedance of the PWM input, the LED driver can be operated as a protected high-side switch.

The TL4242 is characterized for operation from –40°C to 150°C.

An external shunt resistor in the ground path of the connected LEDs is used to sense the LED current. A regulation loop holds the voltage drop at the shunt resistor at a constant level of 177 mV (typical). The constant-current level can be adjusted by selecting the shunt resistance, R_REF. Calculate the typical output current using the equation:

I_Q,typ = V_REF/R_REF

where V_REF is the reference voltage (typically 177 mV) (see Reference Electrical Characteristics). The equation applies for R_REF = 0.39 to 10 .

The output current is shown as a function of the reference resistance in Figure 1. With the PWM input, the LED brightness can be regulated via duty cycle. Also, PWM = L sets the TL4242 in sleep mode, resulting in a very low current consumption of