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CD4536B: Grounding of MONO IN terminal by 10 kOhm resistor or higher

Vigor Vigor
Prodigy 10 points
Part Number: CD4536B

Hi,

the datasheet says on the first page (page number 3-311) that the MONO IN terminal must be

grounded by a 10 kOhm or higher resistor in order to disable the on-chip monostable output.

The logic diagram on page number 3-314 shows that an internal n-channel MOSFET can only switch

the MONO IN terminal to VSS (ground). So why do I need a resistor to connect MONO IN to ground?

On my opinion one could also directly connect MONO IN to ground. Is that true?

Other compatible ICs e.g. MC14536B always directly connect MONO IN to ground if the monostable

output isn't used.

Regards

  • 0
    TI__Guru* 97046 points

    Hi Vigor,

    I agree that the schematic shows what you've described, and directly grounding the MONO IN pin is probably fine.

    This device was released by Harris so long ago that I couldn't find a release date -- I'm guessing about 40 years. TI acquired the parts only to continue manufacturing them in the late 1990's, so we don't have all the details that the original designers did. My assumption would be that the engineer who wrote the datasheet originally had a good reason for recommending a 10kohm or larger resistor to terminate MONO IN, but I don't have any way to verify this. For this reason alone I would still stick with the datasheet recommendation. Additionally, TI can only guarantee what's in the datasheet.