I am trying to design a buck regulator with the following specification: Vin = 24V Vout = 5V I max = 8A Fsw=228k. The load is basically a long strip of RGB LED's. Which in certain cases would be all white for certain durations. I have measured these to be full white at 6.9A (hence 8A design).
I am considering the following high side FET: https://www.farnell.com/datasheets/2311812.pdf
And the buck regulator is LM25085A (https://www.ti.com/lit/ds/symlink/lm25085a.pdf?ts=1635166406663&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM25085A)
I found the following equation for swithcing losses here (https://www.ti.com/lit/an/slyt664/slyt664.pdf?ts=1635224006712&ref_url=https%253A%252F%252Fwww.google.com%252F):
Which if I try to calculate is 24 * 8 * 228k *((17n + 19n)/1.75A) = 0.9W. 1.75A is the source current going to gate and 1.65A is the sink current from the gate (values from LM25085) but for this example this value should be acceptable.
So that would be 45m * 5/24 * (8^2 +(1.6^2/12) = 0.602W
Total losses are therefore around 1.5W.
The only temperature value in the datasheet of the FET is channel to ambient and that is just 2.5C/W
So temp rise is 2.5* 1.5 = 3.75 degrees rise.
That sounds pretty low but I guess makes sense as the package is rated for 25A continuous current.
If I use the DC operation as a starting point, and VDS as max input voltage (24 V), it would seem the safe operating limit is 2A? I am not sure I understand this bit and whether the FET would work in such application? What pw value from the SOA graph should I be using?