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How to convert discrete NexFETs to NexFET PowerBlock

Other Parts Discussed in Thread: CSD16321Q5, CSD17579Q5A, CSD87353Q5D, CSD87334Q3D

In the WEBENCH design I did it came up with two discrete NexFETs.  If possible I would like to convert them to a NexFET PowerBlock. But looking at the PowerBlock data sheets I am not entirely clear on how I should go about selecting a PowerBlock to replace the discretes.  The two discretes specified were 

CSD16321Q5 (VdsMax = 25V, IdsMax = 100A, Rdson = 2.6mOhm)

CSD17579Q5A (VdsMax = 30V, IdsMax = 25A, Rdson = 0.013Ohm)

This is a non-isolated DC-DC buck converting 10.5V-12.6V to 8.0V. 

Thanks, 

  • Robert,
    This sounds like a great application for power block! Power block datasheets are written more from a system level solution, as opposed to discreet FETs , so it just depends on your input conditions and how much power loss you are willing to accept at what given output current. You probably only need a 25V device, although 30V would work too.

    Also sounds like you want something that is good for high duty cycle operation so something like the CSD87353Q5D or CSD87334Q3D might be a good bet.

    I would try our Buck Converter NexFET Selection tool here: www.ti.com/.../fetpwrcalc

    This tool will recommend discrete solutions and a power block solutions, and allow you to compare 1k cost and size as a trade off. In that sense, its a bit more flexible at the FET / power stage side than Webench.

    It's a relatively new tool so I'd love to hear your feedback on the tool if you like it or have suggestions for how it might be better.
  • Hi, thank you for the suggestions and pointer to the tool. The tool picked the CSD87353Q5D as you suggested above. It worked really well. I was quite happy. The only thing I would suggest is some way to get some kind of print out when the final decision is made. If it already does this I did not see the option.