I am using the TPS5420 as a step-down regulator for a solar panel, with the solar panel connected directly to the input of the TPS5420. I am trying to get a grasp for the expected behavior. I have identified that the output power of the TPS5420 (set at 14V) is equal to P = V*I = 14 * (14 - V_diode - V_battery) / R, and the solar cells (modeled as a current source in the schematic), will operate at a power equal to the power output of the TPS5420 plus any power losses.
With this in mind, as the battery depletes in charge starting from 14V, the power demand on the output of the TPS5420 increases. This can be visualized by starting at Voc on the PV curve and moving upwards until the power demand reaches Pmp minus your power losses. What I am wondering, is what will the TPS5420 do once this point is reached? The solar panel can not provide any more power, so either the voltage or current needs to drop. I suspect the voltage will drop, meaning the TPS5420 will no longer be able to output at its setpoint and the output voltage will decrease in order to keep at maximum power and satisfy Ohm's law over the output resistor, but I am not sure!
Thank you for your help!
Fig 1: Simplified Schematic
Fig 2: PV IV Curve