DPI interface for Raspberry pi including backlight driver
From comments
If I take a guess, I would say that if you pushed a current of 40 mA into the LED, it will develop a forward voltage of typically 12.8 volts. This means that you shouldn't have to worry about doing anything about the voltage because it will settle to a value that is suitable for 40 mA flowing through it. So, choose a resistor like 10 ohm that limits current to 20 mA (as per your last question and my answer) and maybe if that looks OK, try lowering that resistor to 6.8 ohms and see what the voltage across the LED is.

So with constant current, isn't the voltage adjusted to dim the load
up and down? So if I wire everything with the TPS to provide a 40mA
constant current, are you saying that it &quot;should&quot; run at 12.8V when at
full power just by itself, then if I dim using the PWM input, it
should lower this voltage appropriately?

Yes, that's what I'm saying - it will produce the right voltage to drive 40 mA through the load because it is the 40 mA that is being measured by the Rset resistor and FB requires 200 mV on that pin to start regulating hence 40 mA through 10 ohm = 200 mV.

Just to say that the driver circuit worked and the backlight dims
perfectly. Thanks! – Bassline Soup