An RJ45 connector drawing can show several different groups of contacts and pins on the same page. For a connector with integrated magnetics—often called a magnetic RJ45 jack, an integrated connector module (ICM) or a MagJack—the cable-side contacts and PCB-side pins do not necessarily share the same numbering or electrical function.
Before creating a footprint, separate the drawing into four groups: cable-side contacts inside the RJ45 mating interface; PCB-side signal and center-tap pins; LED terminals; and shield tabs and mechanical posts. Trace each numbered PCB connection through the product's electrical schematic and locate the same number on the recommended PCB layout. Do not infer the circuit from physical position alone.
Quick answer: An RJ45 cable contact number describes a position in the mating interface. A MagJack PCB pin number identifies a manufacturer-defined connection on the board side. Use the part's schematic and footprint together to determine how they relate.
Before looking at individual pins, confirm that the document matches the exact connector being designed into the PCB. Record the manufacturer and complete part number; drawing number and revision; integrated or separate magnetics; Ethernet application and PHY interface; port count, mounting style and latch orientation; and LED and shielding configuration.
A single character in a part number may distinguish LED colors, latch orientation, magnetic circuitry or mechanical construction. Similar product photographs and matching outside dimensions do not establish electrical interchangeability.
A bare RJ45 jack provides the physical mating interface. The required Ethernet magnetics are selected and placed separately. An integrated magnetic RJ45 jack combines the connector with magnetic components inside the same housing. The exact internal circuit varies by part and may include transformer windings, common-mode components and termination networks. Check the schematic instead of assuming every ICM contains the same components.
The front of an Ethernet RJ45-style jack contains eight mating contact positions for the cable plug. On the board side, solder tails or surface-mount terminals connect the module to the PCB.
| Item | Cable side | PCB side |
|---|---|---|
| Location | Inside the mating opening | Pins or pads attached to the PCB |
| Connects to | Ethernet plug and cable | PHY-side circuit, LED driver and other board circuitry |
| Numbering | Mating contacts, often shown as 1–8 | Manufacturer-defined pin numbers and labels |
| Where to verify | Mating interface view and electrical schematic | Electrical schematic, mechanical drawing and PCB layout |
Some drawings label cable contacts J1 to J8; others use different symbols. PCB connections may be numbered without a P prefix. The labels are drawing-specific.
A transformer transfers an AC signal across an isolation barrier; it should not be interpreted as a direct copper connection between cable and PHY sides. Follow the connector drawing and the selected PHY reference design. See the Intel Ethernet Controllers Common Design Checklist.
PCB-side labels can include TD+ and TD−, RD+ and RD−, TRD0± through TRD3±, CT, VCC, GND or shield-related labels. Their meaning and required connections must be checked against the actual part and PHY. A 10/100 interface and a 1000BASE-T interface may expose different numbers of PCB connections and use different internal magnetic circuits.
Center-tap connections depend on the selected PHY, magnetics topology and complete reference circuit. Identify which winding and isolation-barrier side the tap belongs to; check whether taps are separate or connected internally; review the PHY manufacturer's circuit; and verify any PoE and isolation requirements separately. A reference circuit applies to its own topology and is not a universal MagJack rule. See the TI TIDA-010046 reference design.
RJ45 modules can contain single-color LEDs, bi-color LEDs or no LEDs. Check which pins belong to each side, the colors, whether elements are independent or anti-parallel, and whether series resistors are built in.
LINK-PP drawing LP13012302 Rev A shows a left green LED on PCB pins 11 and 12 and a right yellow LED on pins 9 and 10. Pin 11 is positive relative to pin 12 for the green LED circuit; pin 9 is positive relative to pin 10 for the yellow LED circuit. A 250-ohm series resistor is shown in each LED circuit.
Drawing LP11021127 Rev A shows green/yellow LED elements on both sides: left pins 13 and 14, right pins 11 and 12. Each pair is anti-parallel, so color depends on applied polarity and drive circuit. Do not copy the LPJ16183A28NL LED wiring to this model merely because both have green and yellow indicators.
Drawing LP18042006 Rev A shows a left green LED on PCB pins 15 and 16 and a right yellow LED on pins 17 and 18. Its recommended PCB layout is a top view. The schematic also distinguishes cable-side contacts J1–J8, PCB-side signal pins and VC1–VC4 connections. Use the drawing and PHY/PoE system design together; pin numbering is specific to this model.
Design check: Some connectors include series resistors and others do not. Calculate or verify LED current using the actual connector schematic, supply and PHY or GPIO drive arrangement.
Larger holes or slots can serve different purposes. A metal shield tab may provide electrical connection and/or mechanical retention. EMI spring fingers may contact a panel or enclosure. Plastic locating posts provide alignment and retention. Check the drawing's views, notes, plating and soldering requirements; do not classify a hole based only on its diameter.
There is no single connection correct for every product. The strategy depends on the enclosure, chassis and protective-earth arrangement, isolation requirements, ESD path, EMC objectives and PCB stackup. Some designs connect the shield to a chassis or earth reference; others use a different network consistent with their system architecture. Follow the equipment-level grounding design and manufacturer guidance, then validate through appropriate EMC and safety tests.
Do not add a generic capacitor and resistor network—or connect every shield tab to a particular ground—solely because it appears in another product's schematic.
A recommended PCB layout labeled top view normally describes the specified top/component-side view; a bottom or solder-side view is from the side identified in that drawing; a front view looks into the mating opening; and a side view describes height and board relationships. Verify numbered pin positions, latch direction, board edge and mating-face orientation. Check whether the ECAD view is mirrored rather than assuming a universal convention.
Use exact dimensions and tolerances from the part drawing. Determine whether each value is a finished hole, drill size or another specified dimension; ask the manufacturer if unclear. Confirm which holes require plating or solder connection. Check pad size, annular ring and solder-mask clearance against the fabricator's rules, review assembly requirements, and verify clearance around the housing, shield and latch. Avoid copying a typical RJ45 footprint without comparing every numbered pin and mechanical feature.
| Drawing item | LPJ16183A28NL | LPJG16314A4NL |
|---|---|---|
| Ethernet application | 10/100BASE-T | 1000BASE-T |
| Drawing | LP13012302 Rev A | LP11021127 Rev A |
| Drawing dimensions | 21.25 x 15.95 x 13.45 mm | 21.25 x 15.95 x 13.45 mm |
| LED configuration | Left green; right yellow; 250-ohm series resistor shown in each circuit | Green/yellow on both sides; anti-parallel elements |
Both drawings show the same nominal external dimensions, but their Ethernet applications, magnetic circuits, LED arrangements and PCB-side connections differ. Review the drawings separately before either part is used.
View LPJG16314A4NL product information. For the PoE application example, see LPJG0928GENL product information.
No. Cable-side mating contacts and PCB-side connections are different parts of the connector system. Read their numbering and electrical relationship from the specific drawing.
No. Circuit topology, signal pins, center taps, LEDs, shield tabs and mechanical features can differ. Verify both drawings and the target board.
Use the polarity marks and diode symbols in the manufacturer's schematic. A two-pin bi-color LED may contain anti-parallel elements, so reversing polarity can select a different color. Do not rely on pad shape or pin number alone.
Only after comparing the complete drawings. Matching external dimensions or latch orientation does not prove that signal pins, LED connections, shield tabs or mechanical posts match.
The correct connection depends on the complete system design. Review the enclosure, earth and signal-ground architecture, manufacturer guidance, EMC and applicable safety requirements before selecting and validating a connection.
Contact LINK-PP with the complete part number and intended application, or visit the relevant product page to request the current drawing. For a replacement review, also provide the original part number, PCB revision and required Ethernet speed.
Related reading: RJ45 PCB Footprint Land Pattern Guide.
