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How to convert discrete NexFETs to NexFET PowerBlock

Robert Ritchey
Intellectual 370 points
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, 

  • 0
    TI__Mastermind 18200 points
    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.
  • 0 in reply to Brett Barr1
    Intellectual 370 points
    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.