TPS40170 - RLIM

Hi all,

Would you mind if we ask TPS40170?

<Question1>
-RLIM-
-TPS40170 with NexFETs 24-V Input, 5 V at 10-A Output Synchronous Buck EVM : 16kohm
-TPS40170 with NexFETs 7A using Webench : 26kohm (Please refer to the attachment file)
About using Webench, we could not get the same value RLIM 26kohm using Equation39 on the datasheet.
(1.3A * 7A + 1/2*1.86)*1.25*13mohm=18kohm
So, on the Webench, is there difference of the coefficient?
20151203_TPS40170_WebenchReportsServlet.pdf

<Question2>
When we calculate Iripple, is the following correct?
-ΔIL= (1/fsw) ×(Vout/Vin）×(Vin-Vout）÷L

<Question3>
Equation39 on the datasheet, it shows1.25*XXmohm.
What does the coefficient 1.25 mean? Is this Safety factor?

<Question4>
Rds of FET depends on temparature or ‎variations in manufacturing(manufacture error).
When we use Rds, we guess that the tolerance of the calculation of RLIM will be big.
That's why, our customer increases(improves) the accuracy of overcurrent detection.
So, in order to improve the accuracy of overcurrent detection, is the inserting XXmohm resistor with Low - side FET valuable?
Or, if you have some advice, could you let us know?

As our customer's request, ‎they would like to reduce the error(tolerance) due to Rds of Low-side FET, other external part.

We do need your help.

Kind regards,

Hirotaka Matsumoto