Choice of transistors and frequency for LM5145

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I'm thinking about designing a universal source with LM5145.
any as
Input voltage 48V
Output adjustable 1-40
current 0-20A
driver LM5145 75V Synchronous Buck Controller With Wide Input Voltage and Duty Cycle Ranges
I'm not sure of two things with which TI webench did not help me either

1.Output transistor
Webench can not design a source for example 15V 20A, because does not have the corresponding transistor in the database.
For example, in the database is
**broken link removed**
100V 100A 3,5mOhm Qoss 91nC
Why this transistor does not suit?
What pair of available transistors would be ideal?

2. Switching frequency
LM5145 works in range 100kHz - 1MHz
The higher the frequency, the higher switching losses and the smaller inductors and the capacitors
The question is how to choose the frequency for proposal?
Thank you for your suggestions
 

1) If you actually read the data sheet, the BSC035N10NS5 is rated for 19Amps at 25degC. Obviously, not good for 20 amps.

2) Only you can answer that question. Which is more important to you, smaller inductors (cost) or greater efficiency?
 

I believe there is an error in the datasheet of BSC035N10NS5.When you look at the "Safe Operating Area" curves, you see the the transistor can work up to 30 A @ 80VGS.( page-6)
Can you verify the datasheet information from Infineon.?
 

Her is calculating power lost for any Infeon transistor used s High side Swith with LM5145
output voltage 15V , optput current 2-20A switching frequency 220kHz
Code: 
	         4A	8A	12A	16A	20A		
BSC117N08NS5	0,5	1,04	2,1	4,19	9,87	80V    11.7 mOhm
BSC070N10NS5	0,47	0,89	1,57	2,66	4,54	100V	7,3 mOhm
[B]BSC040N10NS5	0,57	1,04	1,66	2,46	3,56	100V	4,0 mOhm[/B]
BSC035N10NS5	0,62	1,16	1,8	2,63	3,64	100V	3,5 mOhm
BSC030N08NS5	0,6	1,11	1,74	2,5	3,45	80V	3.0 mOhm
[B]BSC040N08NS5	0,49	0,88	1,38	2,09	3,1	80V	4.0 mOhm[/B]
BSC072N08NS5	0,47	0,89	1,58	2,73	4,75	80V	7,2 mOhm
BSC052N08NS5	0,46	0,83	1,36	2,13	3,26	80V	5,1 mOhm
BSC026N08NS5	0,69	1,3	2,05	2,9	3,93	80V	2,6 mOhm
BSC037N08NS5	0,52	0,94	1,5	2,22	3,24	80V	3,7 mOhm
Best choice in 80V is BSC040N08NS5
Best choice in 100V is BSC040N10NS5

Her is power lost BSC040N08NS5 for five different frequency
Code: 
	         4A	8A	12A	16A	20A		
BSC040N08NS5	0,22	0,45	0,87	1,38	2,12	80V	100kHz
BSC040N08NS5	0,49	0,88	1,38	2,09	3,1	80V	220kHz
BSC040N08NS5	0,68	1,15	1,76	2,58	3,66	80V	300kHz
BSC040N08NS5	0,92	1,5	2,24	3,21	4,51	80V	400kHz
BSC040N08NS5	1,15	1,84	2,73	3,87	5,34	80V	500kHz
Power lost is switching + conduction lost over high side trancistor in Watt for current 4,8,12,16,20A
 
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    FvM

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100V 100A 3,5mOhm Qoss 91nC
Why this transistor does not suit?
What pair of available transistors would be ideal?
Click to expand...
Using a too large transistor is surely not optimal, because it causes additional switching losses of transistor capacitances. You are trading switching against conduction losses.
 

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