Logical Descriptions in Footprint Expert

Logical Descriptions are mostly used by the EE engineer in the schematic symbol. The Logical Description defines the electronic function of the device and is not usually imported into a PCB Footprint. The PCB designer is mostly interested in the Physical Description as it defines the physical attributes of the component package that solders to the PCB.

The Logical Description is usually in the schematic Bill of Materials (BOM) and that becomes part of the PCB designer's documentation for the CAD library which ties the schematic symbol with the PCB footprint. Logical Descriptions come from several places and there is no standard format that defines them. To achieve the highest level of automation, everything should be standardized. Even the Logical Description.

Organize the Logical Description by component family. Examples: IC, Transistor, Inductor, Capacitor, Connector, Header, Resistor, Crystal.

Semiconductor datasheets usually provide the Logical Description on the first page of the component datasheet. Texas Instruments primarily produces semiconductors, and their datasheets are meta data friendly to allow you to copy/paste the Logical Description. Put 'IC' before the description.

It is important to note that most library PLM systems are ASCII data and "symbols" are not ASCII. Do not copy/paste symbols from a PDF datasheet into your PLM library. Symbols include:

Here are sample semiconductor datasheets. 

Note: if the Logical Descriptions contain the word 'with', exclude everything after that to keep the Logical Description less than 80 characters.

Discrete components are much more complex than semiconductors because a single datasheet represents multiple devices with different values.

Note: the rule for spaces in the Logical Description

Single capital letters like V, W, A have no space between the value and the letter.

Multiple capital letters like VWM, MHz, GHz have a space between the value and the letters.

Multiple letters that start with a capital letter like ‘Ohm' have a space between the value and the letters.

Multiple letters that start with a lower-case letter like uH, mOhm, uF, nH have no space between the value and the letters.

Note: the rule for commas in the Logical Description. A space always follows the comma:

The component family always is first, followed by the package style and function and last the values.

Resistor: Resistor, Chip, Thick Film, 196K Ohm, 1%, 1/8W

Capacitor 1: Capacitor, Chip, Multilayer Ceramic, 2.2uF, 10%, 10V, X7R

Capacitor 2: Capacitor, Molded, Tantalum Polymer, 22uF, 10%, 50V, X7R

Inductor: Inductor, Low Profile, IHLP Power, 150nH, 26A, 2.5mOhm

Diode: Diode, TVS, 350 VWM, 564 VC, 64A

Transistor: Transistor, Bipolar NPN, 40V, 200mA, 300 MHz, 625mW

Crystal: Crystal, Mobile Communications, 38.4 MHz

Connector Logical Descriptions can be organized by these parameters.

Example: Connector, 140 Position, 0.80 mm Pitch, Board-to-Board, Dual Row, Receptacle, Vertical