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DC Operating Conditions

Kika
Intellectual 420 points

Hello,

We had this question from our customer.

In the LM4F230E5QR's datasheet  "Table 25-2"

the parameter "Low-level output voltage " says MAX  VOL= 0.4V

whereas "Low-level sink current"  parameter IOL says 8-mA Drive, VOL=1.2 V.

Please let us know how this is related.

Regards.

  • 0
    TI__Expert 6140 points

    Kika,

     

    In the paragraph above that table it explains that at 8mA drive strength you can use 4 GPIOs to sink up to 18mA each and at that setting Vol = 1.2V:

     

  • 0
    Guru 35555 points

    Kika said:
    "Low-level sink current"  parameter IOL says 8-mA Drive, VOL=1.2 V.

    That is not a specification for VOL  - that the condition under which you can have IOL of 18mA.

    It is left as an exercise for the student to estimate, from the figures given, the effective on-resistance of the output stage...

  • 0 in reply to Andy Neil
    Guru 47900 points

    Pardon - in the interest of safer, more conservative "specsmanship" I interpret the spec as suggesting that VOL may rise to 1.2V when 8mA of current flows - not when 18mA flows.  The reference to 18mA current flow has not been promoted to the full, written spec - and I would not base a design upon any guarantee nor assurance that VOL will "hold" @ 1.2V when 18mA flows...  Surely 18mA can be supported - but the spec does not list VOL for such condition...

  • 0 in reply to cb1
    Guru 35555 points

    cb1- said:
    I interpret the spec as suggesting that VOL may rise to 1.2V when 8mA of current flows - not when 18mA flows.

    I disagree.

    I think the text & table quoted by the previous posters clearly do show that 18mA is allowed (subject to the restricions stated) and, at that current, VOL may rise to 1.2V.

    cb1- said:
    Surely 18mA can be supported - but the spec does not list VOL for such condition...

    Yes it does - it is 1.2V (max): 

     

  • 0 in reply to Andy Neil
    Guru 47900 points

    I was wrong - see now that VOL is listed @ 0.4V @ 2, 4, & 8mA current flow (bet that it varies between 2 and 8 though) and that indeed - VOL = 1.2V @ 18mA.  Somehow I missed the 18.0mA entry at 1st reading.   In defense - duplicative current listings (2-mA Drive...2.0 mA) w/in the present chart probably would offer more comfort/clarity if VOL instead was listed & thus matched to the specific current drive.  Again - both responding posters appear correct...

  • 0 in reply to cb1
    Guru 35555 points

    cb1- said:
    VOL is listed @ 0.4V @ 2, 4, & 8mA current flow (bet that it varies between 2 and 8 though)

    Yes, I suspect that it does!

    Agree that the clarity of the chart could be better - the column title, "Parameter Name" tells far short of the full story...