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What affects VOH_min and VOL_max? Is it just the current being sourced/sunk by the pin? Or are there manufacturing variances or temperature effects etc that can swing the output voltage away from supply/ground even with no or very little current in the pin?

Edit: What affects VOH and VOL? What are the major contributors causing VOH be lower than supply and VOL be higher than ground?

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  • \$\begingroup\$ VOH_min and VOL_max aren't affected by anything : they are part of the specification. VOH and VOL on the other hand are affected by all sorts of things including process, temperature, supply voltage, and load impedance. \$\endgroup\$
    – user16324
    Sep 14, 2020 at 21:28

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For a given specified value of \$I_{OL}\$ and \$I_{OH}\$, the actual (not specified) values of \$V_{OL}\$ and \$V_{OH}\$ are subject to the usual influences: temperature, manufacturing variation, supply voltage, aging, packaging resistance differences, and so on. Which of these might be a "major" contributor depends a great deal on the specific device design, fabrication, and usage.

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CMOS MCU outputs will be driven deep into "triode region", where the FET looks almost like a linear resistor.

If the external load requires just nanoamps of DC leakage current, the Vout will be either at GND or at VDD, regardless of how large the CMOS FETs are.

For 1Kohm or 100ohm Rloads on the PCB, the Voh_min and Vol_max will be set to allow/sell/recover_development_costs for all output drivers that have all the FET stripes intact (no missing bits of metal), and provide acceptable output current for VDD-10% and for VDD+10%.

Do not expect any temperature testing; that is slow. Varying VDD+-10% is very fast, so can be done.

The output drive strength, and also the output linear_resistance, varies inverse linear with the VDD. Expect the drive strength (its in "triode region") to vary +-10% if you vary the VDD +-10%. Notice the ringing of VDD, nanosecond by nanosecond, will cause a variation in drive strength, will cause a variation is DELAY and thus will cause timing jitter as the program_execution charge demands vary.

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