Hello Ti,
We are designing pfc with UCC28064A and we did not realize how to select RTset value.
It seems the Rtset value, not only affect maximum frequency, but also affect minimum frequency.
Can you give me a guideline about selecting RTset? What is the trade off for selecting it?
Hello,
I reviewed the data sheet and section section 9.2.2.9 below give guidance on selecting the resistor on the TSET pin. They called it RT instead of RTSET.
However you should be able to use the calculations to properly select RTSET.
https://www.ti.com/lit/ds/symlink/ucc28064a.pdf
Regards,
Hello Mike,
In SLUAA28 document says RTSET also determine minimum period(or max frequency).
Can you please explain more, how RTSET affects ton time? What is the operational principle?
Can you please explain more, how RTSET affects toff time? What is the operational principle?
Hello,
The on time Ton of the UCC28064A is determined based on the comp output voltage (Vcomp), the peak of the link voltage (VINACPK) and the value of RTSET below described in the equation below.
The off time (toff) is generally based on how long it take the boost inductor (L) peak current Ipk current during the switching period as described below. This is based on V = L*di/dt.
toff = Ipk*L/Vin
Regards,
