Let's say that our Vin = 9V, Vout = 5V. Hence our duty cycle D = 5/9.
Let's say that our switching frequency is 100kHz.
Consider T_on as the time the HSFET is on. So our T_on in this case is:
T_on = (1/100kHz)*(5/9) = 5.5us
If I_Load increases, we will need more time that HS FET is kept on. So that will mean that T_on increases. So this 5.5us will increase.
My question : Does the equation I used to calculate 5.5us only apply for no load conditions? I assume I need to have an extra scaling factor which repersents the PWM reacting to increased load and hence inceasing Ton?