Electronic – Classification of VDD and VSS pins

kicadmicrocontrollerpowerschematics

I am creating a library component for KiCAD using a convenient online app at: http://kicad.rohrbacher.net/quicklib.php. The component I am making is the Microchip PIC24EP512GU814 in LQFP http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en554337.

The app asks me to assign a type to each pin. The types avilable are:

Input
Output
Bidir
Tri-state
Passive
Unspecified
Power Input
Power Output
Open Collector
Open Emitter

I must now assign one of these types to the VDD and VSS pins.

My best guess is that VDD should be assigned as Power Input. Would VSS also be considered as a power input?

Perhaps since VDD is analogous to VCC (and VSS to VEE), I could classify VDD as an Open Collector (and VSS as Open Emitter). However I'm not sure if VDD and VSS can be considered as "open" for an IC.

What should VDD and VSS be mapped to?

Best Answer

I would recommend using Power Input for both VDD and VSS (or any power pins on an IC for that matter). If you choose to use these types of pin labeling, then it allows you to verify that all power supply pins are connected and that there is a source that can provide power.

If you set VDD or VSS as a Power Output then the software will see it as something that provides power for the circuit. This would also give you an error if you have multiple chips on the same power supply (e.g. two of these chips). The output of a linear regulator would be a good example of a Power Output.

Making both VDD and VSS the same is a bit counter intuitive compared to current flow, but these are being used as system terms, not electrical current/voltage terms.

Related Topic