Embedded project needs devices which can work continuously at +125 degree C

I have selected the battery charger IC as LT1513 and boost regulator IC as LT3581.

These are the links for the datasheets.

https://www.analog.com/media/en/technical-documentation/data-sheets/1513fas.pdf

https://www.analog.com/media/en/technical-documentation/data-sheets/3581fb.pdf

These are my calculations for battery charger and boost converter (find attachment)

The first two calculations are for battery charger.

Battery voltage is 3.6V and I chose Vbat as 4.2V because for each Ni-CD cell I read that the max charging voltage should not exceed 1.5V and so it will be 1.5V * 3 = 4.5V.

So, I chose 4.2V.

Just give me a confirmation whether my R1 value calculation is okay or not ?

For boost converter please check the calculations in the attached PDF.
Refer page no 13 of datasheet (LT3581), Boost Design Equations.

I require max 1.2A from the boost converter.

I am having problem in Step 7 of Boost Design Equations (page 13 of datasheet).
I will not be using PMOS and I want to know how to calculate Cout = Cout1 + cout2.
Should i just remove the Rdson_pmos from the equation of step 7 or replace it with 1 ?
-.9999562000
Also I have issue with step 10 of the equations that is for Rt. In attached pdf I am getting negative value for Rt that is

-0.9999562000