I have a 3 color LED that I'm controlling from an STM32. VDD for my mcu is controlled by a switching regulator set to 3.0v . Unfortunately the forward drop on the the green led is 3.2 volts. This forces me to source current from the battery attached to my board ( 3.8v lipo). So the anode of each led is connected to the battery, and each cathode is connected to a resistor and then an io pin of my SMT32.
If you cruse the SMT32F* reference manuals you'll find out that each IO pin has a set of protection diodes attached (see below). The problem is when I shutdown the Switching regulator it effectively ties vdd to ground. So we have a path from the battery through each of the leds through a resistor finally though the protection diode to vdd which is tied to ground. I need to turn off the switching regulator to conserve battery power.
My question is does anybody know the forward drop on these protection diodes? If its high enough then i don't have to worry about current flowing through the leds and protection diodes to ground. If it isn't I'm assuming I'll have to put a between the mcu and the regulator unless somebody else has a clever soltuion to this problem.