Forum Post: RE: LM3150 datasheet formulas vs. Webench results

Hi Kevin,

Thank you for your reply, this answers question #2 and 3. I now understand that results from the datasheet equations and WEBENCH should not be mixed. Also, thanks for the tip on the feedforward cap.

Still, question #1 is still unanswered.

Look at the R_LIM calculation at page 19 in the datasheet: R_LIM = (10.4 x 0.014) / (75 x 10^-6) = 1.9 kΩ
Here I_LIM-TH(T_j) is 75 x 10^-6. When using this I_LIM-TH(T_j) value in equation 24, you get an I_LIM-TH value of 60uA.
But I_LIM-TH is a LM3150 constant which typically is 85uA (see bottom row in Electrical Characteristics on page 3)
IMHO, this example gives a incorrect R_LIM value of 1.9 kΩ when the correct value should be 1.3 kΩ

So once again, which is the correct I_LIM-TH to use in equation 24?

Best Regards
PO