I'm working on an extremely compact circuit, and I'm trying to figure out the best way to current limit three LEDs. The issue is that they are RGB LEDs, so there are actually 9 of them. They dont need to be driven individually, so only three control inputs are needed, but I'm having trouble figuring out a compact way to tie them together.
I can't just put them in parallel (because of possible minute Vf differences), and I don't have enough voltage to put them in series. The voltage drive varies between 3-6 volts, and I want a current of around 10mA in each of the LEDs, +/- 10%. I'm controlling them with a 1.8V mcu, so I was just going to use a mosfet for switching, but I need something to limit the current more precisely than just having a resistor. Any thoughts?
It's very important that it be compact, because every mm2 counts here. I know I could use a purpose made chip, but I haven't found any that are small enough and have enough inputs. I certainly wouldn't want to be using 9 PSSI2021SAYs (although three would be ok, but how do you tie the LEDs together?).