Couple questions about LED driver IC TL4242

[Joshua_S]

TL4242 is a constant current LED driver IC. I am confused by the "Constant Current".

If there is a PWM input at Pin1, then the output Pin6 is PWM? If there is a shunt resistor at Pin 4, this pin is also PWM? How does TL4242 control the brightness according to the block diagram?

My thought is: if LED is working at constant current, Pin6 and Pin4 are constant voltage outputs so the current is also constant. But how a PWM signal can generate a constant voltage output? It looks like there is internal linear voltage/current regulator?

 

[PaulStoffregen]

I believe the PWM signal essentially turns this chip on/off (where "off" is a state where it can turn back on very quickly). When PWM is low, the current is zero. When PWM is high, it's whatever current makes the resistor give 0.177V at the REF pin. So if using a 1 ohm resistor, 177 mA. It looks like just a linear current regulator with fast on/off control.

The main reason to use this chip rather than just a resistor in series with the LED and a big transistor is it keeps the on current fairly constant even as the power supply changes. But it's linear so it looks like it would get pretty hot. Hope it's soldered well to a thermal pad/vias and a big ground plane in the PCB.