I have constructed and tested a circuit that achieves MPPT of solar panels. The MPPT circuits involves current sensors that requires 3.3V and -3.3V and also the MOSFET and MOSFET drivers that require 8V. To obtain these voltages, I am using an auxiliary power circuit that involves low power COTS chip converters. It begins by feeding the primary input to a LMR14006 based Buck converter. The output 3.3V is then used to feed the current sensors, a TPS6040X inverter that provides the required -3.3V and the LMR62421 boost converter that provides the required 8V. Please see the attached image which shows the auxiliary circuit component of my MPPT schematic.
As a side note, the MPPT circuit is intended for handling higher powers than that of the aforementioned auxiliary circuits. Its details are not important here as the source of my problem is not from them.
The issue I am getting is that the LMR14006 and (especially) the LMR62421 are not providing me a consistent 3.3V and 8V. When I connect an input voltage of 6V (and short circuit the input kill-switch in my schematic) and don't run any power through my MPPT circuit (easily achieved by turning off the MOSFETs), the LMR14006 and LMR62421 generates the required 3.3V and 8V. The resulting idle current from the 6V input is measured at 0.035A. However, once I begin running power through the circuit which means the MOSFET drivers will become a heavier load, I noticed that the LMR14006 will now drop its output to 3V and the LMR62421 drops its output to only 5V!
To verify that this problem exists on the auxiliary circuit side, alternatively to running power through the MPPT circuit, I connected an external 120 ohm resistor to the supposed output 8V of the LMR62421. Once again, the LMR14006 outputs 3V only and the LMR62421 outputs 5V instead of the originally desired 3.3V and 8V. Why is this happening?
As an additional note, I also noticed that the feedback voltage of the LMR62421 drops from the datasheet specified value of 1.225V to around 790mV. By the way, the TPS6040X voltage inverter is working as intended and I have no issues with it.
Better, but not good enough: