TPS568215: Switching frequency discussion

Hi Brian,

I don't find the Vin value but I think the min on-time is triggered due to the low duty and high frequency. That means the frequency would be limited.

Under this condition, the on-time is constant and the frequency would be changed with the duty as below. 

D=Ton*f

You can refer to the below equation to calculate duty.

D=(Vout+RL*Iout)/Vin.

You can see the duty is increasing as the output current increasing.

Then the frequency would be increasing as the output current increasing.

You can test the on-time to validate my guess.

Besides, there's another possible reason to do with frequency and output current.

You can refer to the below threads.

https://e2e.ti.com/support/power-management-group/power-management---internal/f/power-management---internal-forum/1130653/tps568215-fsw-tolerance-under-light-load-condition/4196136?tisearch=e2e-sitesearch&keymatch=%20user%3A519969#4196136

Please let me know if you have further questions.

Hi Brian,

Usually we think D=Vout/Vin, but it doesn't take the resister of inductor into consideration.

Actually the mean voltage of SW is Vout + V_inductor, and V_inductor equals RL*IL, where IL_average = Iout here.

So D=(Vout+RL*Iout)/Vin.

Regarding the website, I have sent you an email with attachment.