I was having trouble with consistently entering VLPS mode (Very-Low-Power Shutdown mode) with a FRDM-KL03Z development board. It appears that light shining on the LED hinders the KL03 MCU from entering VLPS mode. Once in VLPS mode, the addition of light does not appear to affect VLPS mode. Apparently the photovoltaic properties of the LED are feeding a small amount of voltage to the MCU, and somehow corrupting entry into VLPS mode. I'm wondering if anyone has an explanation for this, or has had a similar problem. My final product won't have LED's, so it's not a huge concern for me presently, but it could really mess up some products. Putting tape over the LED solved the problem, as did also configuring the pins connected to the LED as ALT0 inputs. Any comments would be appreciated.
A clarification: The LED I am referring to on the FRDM-KL03Z board is the tri-color red/green/blue LED. I had previously reconnected the red & green parts of the RGB LED to PTB3 & PTB4 (with open drain outputs) to make the normal outputs available for other use; that may be a factor.