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I started a new design based on a PIC24EP256GP202. I was interested in finding how much current can a single pin sink/source, but the datasheet looks a bit confusing to me:

The Absolute Maximum Ratings:

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Is the current sink/source capability of a pin 3.5 mA (= 15 mA / 4) or 3.125 mA (= 25 mA / 8)?

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2 Answers 2

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This might help: -

enter image description here

It basically shows where your figures come from graphically. I'd go by these numbers and note the absolute max rating line dotted across the centre of each graph.

Note that some pins are called x4 and some pins are called x8 capability. Those with x8 are twice as good at driving compared to x4 pins.

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  • \$\begingroup\$ Why do the sinking (VOL) and sourcing (VOH) capabilities differ that much? I thought that modern CMOS MCUs have the same sinking and sourcing driving power, unlike the old TTL ICs.. \$\endgroup\$
    – m.Alin
    Jul 2, 2013 at 12:19
  • \$\begingroup\$ @m.Alin Maybe I'm reading the graphs wrong but I don't think they do - the 8x pins are both max limited at 25mA and Voh drops down 0.5V (approx) and Vol rises approx 0.4V \$\endgroup\$
    – Andy aka
    Jul 2, 2013 at 12:46
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Do not look at the absolute maximum ratings when trying to determine the proper operating range for the source / sink current ratings for the pins. Microchip as already tried to tell you that in the notes under the table, albeit in different words. The absolute maximum ratings are there as a guide to give indication of just how rugged the part is under abuse level conditions. The part is never expected to be used at those levels.

What you want to do instead is to study Table 30-12. This table gives you the specified voltage levels that the I/O pins will attain worst case at particular current operating levels. Use these as a guide to loading the pins but still maintain the output drive voltage levels needed for the application.

Do keep in mind that you cannot put these loads on all pins at once. If you do you will quickly exceed the absolute maximum ratings putting the part into the "you are hurting me" danger zone.

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  • \$\begingroup\$ Why do the sinking (VOL) and sourcing (VOH) capabilities differ that much? I thought that modern CMOS MCUs have the same sinking and sourcing driving power, unlike the old TTL ICs.. \$\endgroup\$
    – m.Alin
    Jul 2, 2013 at 12:17
  • \$\begingroup\$ @m.Alin - Each manufacturer chooses to design and specify their devices in a manner that they think provides a best fit for their customer requirements. CMOS structures can be designed to offer symmetrical source and sync capabilities but they do not have to be designed that way. Even if they were designed one way the manufacturer may choose to specify the Vol and Voh at particular Ioh and Iol levels to provide compatibility guarantees to certain logic families. Obviously in this case Microchip chose to use the old TTL standard for the Vol and Voh numbers. That is rather common!! \$\endgroup\$ Jul 2, 2013 at 12:52

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