Hi,
a bit confusing post.
I recommend to ask only one dedicated question at a time....
So what´s your main question? I´m looking for question marks.
is it really realistic for the IC to have 70C ambient as is in datasheet?)
In automotive or industrial environment an ambient temperature of 70°C isn´t unusal.
--> But you are free to choose any other ambient temperature that fits to your application.
how do i choose capacitor now?
There is a chapter in the datsheet. But many parameters depend on your setup or requirements.
Lucky you there are some example circuits. There you may find some "usual" values.
Additionally there is a complete design example. What else information do you need?
what about capacitance and voltage?
For more detailed capacitor value selection you may use the formula with delta_V_out. The less ripple you want the bigger capacitor you need.
Voltage: As with every application. The capacitor voltage rating needs to be higher than the expected voltage at this node.
How reliable are the voltages? If very reliable then you need less headroom. Like with a regulated input voltage.
But - for example - at a 12V automotive applicaton you won´t use a 12V rated capacitor, because the end_of_charge voltage is 14.4V and you may expect a lot of ripple. I´d not use less than 25V rated capacitors. Tantalum are more prone to fail on short overvoltage peaks...add a higher margin.
You will find this information in your capacitor´s datasheet.
Also what would be good software to design this IC, i have eagle cad for student but i think even windows 10 search is better than that...
Don´t complain about a software as long as you aren´t familiar with it. Dont judge a book by it´s cover. Better learn how to use it.
There are many many users they won´t miss EAGLE anymore.
No need to "design this IC". EAGLE is a schematic an PVB layout sofrware , no IC design software.
Maybe have to manually insert the package...
LTC1625 comes with standard IC packages. It´s not more effort than copy and paste.
After you have chosen the correct package from any other EAGLE library it´s just two mouse clicks to insert it - (completely with all descriptions...) into your library.
I´m using both. EAGLE and LinearTechnolgy datasheets for decades now.
Klaus