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CSD18532NQ5B: Logic level

Alfred Fuchs1
Intellectual 320 points
Part Number: CSD18532NQ5B
Other Parts Discussed in Thread: CSD18532Q5B

I saw that the FET above is listed as a logic-level FET @ TI.

It has a typical gate threshold voltage of 2.8V and a max. of 3.4V.

Just wondering: Is there an (more or less) industry-agreed criterion what constitutes a logic-level FET? 

Some go up to 4.5V, but TI's filter apparently not.

My personal opinion: Vgsth should be 2V or lower so that at venerable TTL-high(min) of 2.4V it is clearly turned on.

Actually that would have to be the threshold maximum.

I think we can agree that then it is a logic-FET for sure, even if some logic families nowadays may have lower supply voltages.

But marketing guys may well disagree with me, so - being an engineer - I'd prefer to have a hard rule.

There must have been a time when this term first came about. Was it with HC or with CD4000...? I do not know.

Just wondering how TI does it officially.

  • 0
    TI__Mastermind 32415 points

    Hello Alfred,

    Thanks for your interest in TI FETs. In my experience, traditionally a logic level FET can be driven by 5V and has Rds(on) specified down to VGS = 4.5V. The term logic level is indirectly related to threshold voltage. For TI FETs, any device with Rds(on) specified at VGS = 4.5V or below is considered to be logic level. All of TI's low voltage (BVDSS <= 30V) and a portion of our mid voltage (BVDSS >= 40V and BVDSS <= 60V) FETs are logic level with a few exceptions. All of TI's 80V and 100V FETs have Rds(on) specified down to VGS = 6V and are not considered logic level devices. There is a mistake in the selection table on TI.com with regards to the CSD18532N15B. It is NOT a logic level FET as the minimum VGS = 6V where Rds(on) is specified in the datasheet. This is being corrected. The CSD18532Q5B is the logic level version of this device. Sorry for any confusion.

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Intellectual 320 points

    Very interesting and surprising (not to use Vgsth), but makes a lot of sense actually.