When we refer to PMP30308 reference design ,we can get Rt=200K and CT=470pf and the frequency =200KHZ.
But when we use Frequency=200KHz and CT=470pf and Equation 5 as the picture shows 
we can calculate Rt= 183K Not 200K ,Is it right ? If it is right , when we want to get Frequency =1/3*200K=67kHZ then Rt=566K.
The following picture shows the process of calculation .
Hi Brigitte
1:The measured figure of Frequency (Figure 2) is not accurate , For the RT=200K CT=470pF, we can easily conclude that the Fs=200Khz, But when we want to get 67kHZ, it is not easy to get the value of RT from the curve .
2:For Rt=200kHZ and Ct=470pf , there are two different frequency 300kHZ (From data sheet )and 200kHZ(From PMP30308)
How to explain this difference . 
3:what you really mean is that we can measure the practical frequency to verify Figure 2 after we calculate the Frequency with formula 5.
Thank you for your reply
