I am modifying a design that uses the MP3306EG-LF-P-Z :
It is used with 2 LED in series (the forward voltage of each LED is 3 V). There is a 0.4R resistor in series with the LED (R20). The resistor is connected to a microcontroller, it was previously used to measure the current passing through the LED. The driver is controlled by a fixed PWM on the PWMI input, and another PWM on the EN input (5 ms on, 5 ms off, and so on).
I plan to remove the series resistor R20 because I do not need to measure the current anymore. I have several questions:
- Is it advisable to have a series resistor with the LED (other than being able to measure the current) ? Do I need to put a 0 ohm resistor, or is it OK if I put no resistor at all ?
- If I remove the 0.4R resistor, will there be a difference (even a tiny one) in the current passing through the LED, for the whole range of the input PWM ?
I would expect that there is no difference given that it is a constant current driver, but I want to make sure.