Dear Sir/Madam,
I have a problem on designing and choosing component values for the TPS54061 Buck converter. I am trying to follow the detailled design procedure that is on the part datasheet. I know there is the WEBENCH Power Designer to help me, but as I am completing an apprenticeship, my goal is to understand the process of designing an electronical system.
While I was following the procedure and trying to determinate the switching frequency that is adapted to my needs, I saw that there might be errors in the equations (6) and (7) that are used to calculate the switching frequency:
As you can see on the screenshot above, in the denominators of these 2 equations, there is "Vin-Io*Rhs+Io*Rls" or "Vin-Icl*Rhs+Icl*Rls". The problem is that in the procedure, it is said that Rls=10kΩ and Rhs=Rls*((Vout-0.8)/0.8).
As the minimum output voltage is 0.8V the value of Rhs will always be higher than Rls and the problem is that with the equation 6 and 7, we can only find negative switching frequencies...
Here are the values I used for these equations:
fdiv=1
ton=120ns
Vout=3.3V
Vin=28V
Rls=10kΩ
Rhs=31.25kΩ
Io=100mA
Voutsc=0V
Rdc=5Ω
Icl=0.35A
I don't know if the problem is coming from Rls and Rhs or from the equations, but I find a negative result (and that is not in the allowed range of frequencies). For exemple on equation 6, I find fsw(maxskip)= -3.99MHz...
If you could provide me a solution so that I am able to calculate switching frequency, I would be pleased.
I look forward to your reply and help,
Yours Sincerely,
Thomas
