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LM5146: Question about the FETs in my webench design

mark ross
Prodigy 20 points
Part Number: LM5146
Other Parts Discussed in Thread: CSD19534Q5A, CSD19537Q3, LM5013

Tool/software:

The electrical BOM says the fets are M1 and M2, manufacturer is NA and part number is IdealFET. So obviously this is not correct, the FET does not exist or is not in the database. The only parameters they are giving me is VDSMax is 200V and IdsMax is 7.251 amps.

Ok I guess I have to find my own FET, but here is my concern, with no other design data for these, when I look at the schematic, it appears that these are N channel depletion mode based on the schematic symbols. How can I verify if this is correct?

Design in question says Design : 4 LM5146QRGYRQ1

  • 0
    TI__Guru 62817 points

    Hi Mark,

    I'm not sure why WEBENCH isn't selecting FETs. The LM5146 is a 100V rated device, so 100V FETs should be fine.

    If you can fill out the LM5146 quickstart calculator, I can review your design and recommend some FETs.

    https://www.ti.com/tool/LM5146DESIGN-CALC

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 20 points

    Our only critical issues are this power supply is going on various electrical forklifts and my supply can be 9 to 80V with typical being 24 and we need about 3.5A so we put in 5. Other than that, nothing is critical. When I put in those parameters, ignore the others, I get two different FETS, NVMFS6B25 and NVMFS6B14L both which are flagged as obsolete at distributors. But it did answer my question partially. Those two parts are N Channel. The data sheet schematic symbol looks like depletion mode and so does the transistors in the calculator, but it isn't specifcally called out. 

  • 0 in reply to mark ross
    TI__Guru 62817 points

    Hi Mark,

    The data sheet has the symbol for a power MOSFET. Check with onsemi for replacements of the B25 and B14 100V FETs (if you need Q grade). Otherwise, TI has the CSD19537Q3, CSD19534Q5A 100V commercial-grade FETs.

    Note if the load is only 3.5A, you could use a converter here (with integrated FET), e.g. LM5013.

    Regards,

    Tim