How to Choose a Quad-Port Gigabit LAN Transformer: 72-, 88- and 96-Pin Footprints, PoE and Temperature | VOOHU

How do you choose a quad-port Gigabit LAN transformer? A four-port device can reduce package count when four copper Ethernet ports sit together in a switch, gateway or controller. The package name alone is not enough, however. A 72-pin device may use a long inline footprint, while 88- and 96-pin devices use different block-style hole patterns. Pin pitch, port order, PoE center-tap routing and operating temperature also change with the product. Selecting only by “quad-port Gigabit” can leave a board that cannot accept the component or a schematic whose center taps do not match the intended power path.

VOOHU offers100/1000BASE-T LAN transformersin single- and multi-port, DIP and SMT, non-PoE and several PoE configurations. This article uses four VOOHU products—WHDG72303G, WHDG88403G, WHDG88409PG and WHDG96503PTG—to show how the 72-, 88- and 96-pin mechanical branches differ, then brings PoE capability and temperature into the decision. These checks remove unsuitable options before detailed pin mapping and sample qualification begin.

1. Group quad-port Gigabit LAN transformers by PCB structure

Each Gigabit Ethernet port uses four differential pairs. A quad-port transformer therefore brings four complete port groups into one package. It saves component count, but it also concentrates more differential traces, center taps and port labels around one footprint. Start with the mechanical drawing. Record the package envelope, total pin count, pitch, row spacing, recommended hole diameter and Pin 1 orientation before deciding whether a candidate fits the board.

A 72-pin quad-port transformer follows a long inline layout

WHDG72303Gis a 72-pin DIP device with 1.78 mm pitch. Its body length is 65.70 ± 0.50 mm and its maximum height is 12.00 mm. The recommended holes run along the long axis, which can suit four adjacent RJ45 connectors. The tradeoff is the amount of board edge consumed. When the enclosure cutouts and jack spacing are fixed, place the transformer outline, differential-pair exits and port order into the early PCB floorplan.

An 88-pin package concentrates four ports in one area

WHDG88403GandWHDG88409PGare 88-pin DIP products with 1.65 mm pitch. Their bodies are approximately 29.00 × 26.50 mm with a maximum height of 14.50 mm. This block-style footprint suits layouts where the PHY and four RJ45 connectors are grouped closely. The two products have similar mechanical outlines, but WHDG88403G is non-PoE and WHDG88409PG supports PoE+. Similar pin count does not remove the need to check the internal schematic and center-tap functions.

A 96-pin product needs its own PCB library

WHDG96503PTGuses a 96-pin DIP footprint with 2.0 mm pitch. Its body is approximately 28.25 × 28.90 mm and its maximum height is 14.50 mm. Although it also looks like a block package, its hole count, pitch, group spacing and Pin 1 position differ from the 88-pin layout. Moving from a 72- or 88-pin device to this product requires a new library and another routing review.

2. Decide whether 72, 88 and 96 pins are interchangeable

Pin count is a useful search filter, not proof of interchangeability. Mechanical fit comes first. Hole count, hole locations, pitch, row spacing, body keepout and Pin 1 orientation must all agree. The 1.78 mm pitch of the 72-pin product, 1.65 mm pitch of the 88-pin products and 2.0 mm pitch of the 96-pin product belong to different PCB grids. Extra board area cannot correct a mismatched hole pattern.

The second check is the circuit. Label the four ports A through D and map every PHY-side pair, cable-side pair, polarity, center tap and no-connect pin. A multi-port pin sequence does not always follow a simple port-by-port numerical order. A replacement review is easier when the schematic net name, transformer pin and PCB pad appear in one mapping sheet. This exposes crossed ports, reversed pairs and incorrect center-tap routing before the board is built.

The four products in this article all target 100/1000BASE-T. Their specified turns ratio is 1CT:1CT ±5%, open-circuit inductance is 350 µH minimum, and isolation is 1500 VAC at 1 mA for 60 seconds. Those shared electrical values still do not establish pin-to-pin compatibility. PoE capability, temperature range, footprint and internal connections must also match the design.

3. Match PoE capability with the thermal condition

A non-PoE product belongs in a port where power is not carried through the transformer center taps. A PoE+ design needs magnetics whose center-tap routing and current capability match the PSE or PD circuit. Substituting a non-PoE device into an energized center-tap path, or treating every 88-pin product as electrically equivalent, can cause power-up failure, DC bias or excessive temperature rise.

WHDG88409PG and WHDG96503PTG are specified for IEEE 802.3at operation with 720 mA current capability, making them appropriate starting points for quad-port PoE+ designs. The 720 mA figure defines a component capability; it is not a shortcut for total switch power. The PSE or PD architecture, current per pair, supply voltage, cable drop, conversion efficiency and cooling all affect the final power budget. Apply the intended load to the actual port configuration during qualification.

Temperature separates the options further. WHDG72303G, WHDG88403G and WHDG88409PG are specified for 0 to 70 °C operation. WHDG96503PTG covers -40 to +85 °C. Outdoor cabinets, fanless switches and boards near DC/DC converters require the ambient temperature and component temperature rise to be considered together. A room-temperature link test cannot qualify a 0 to 70 °C product for a sub-zero requirement.

4. Four VOOHU quad-port Gigabit LAN transformer options

All four products are quad-port Gigabit DIP LAN transformers. Their main selection differences are the PCB structure, PoE capability and operating temperature. Use the existing hole pattern and power architecture to narrow the branch, then review the product schematic and electrical limits.

WHDG72303G and WHDG88403G provide two different non-PoE layout branches: a long 72-pin footprint and a compact 88-pin footprint. WHDG88409PG adds a PoE+ option in the 88-pin mechanical family, but its schematic must still be reviewed before an existing non-PoE design is reused. WHDG96503PTG combines a 96-pin footprint, 2.0 mm pitch, PoE+ and -40 to +85 °C operation for designs that need a wider temperature range and can support a new PCB library.

5. Replace a product on an existing PCB in three steps

Overlay the hole pattern and body outline

Export the existing PCB hole map and overlay it with the top-view drawing of the candidate. Check hole diameter, pitch, row spacing, component outline, Pin 1 and routing keepout. The recommended hole diameter is 0.90 mm typical for the four products discussed here, but their hole groups are different. A common drill size does not create a common footprint.

Map all four ports pair by pair

Mark ports A through D in the schematic, then map each port’s four differential pairs between the PHY and RJ45. Include every center tap, power function and no-connect pin. If the current net names use only TX and RX without a port identifier, update them before the replacement review. Clear port labels make a rotated component or changed pin sequence much easier to detect.

Set the PoE and temperature boundaries

Identify whether all four ports are powered, only selected ports carry PoE, or the design is entirely non-PoE. A powered design also needs the PSE or PD role, target current and maximum ambient temperature. For a wide-temperature product, include the required cold-start link condition. Completing these decisions before requesting samples prevents a mechanically correct sample from failing the power or temperature requirement.

6. Qualify the sample with all four ports active

Inspect soldering and static connectivity

A quad-port DIP component has many through-hole joints. After wave soldering, inspect for bridges, insufficient solder, open joints and an incorrect Pin 1 orientation. Check continuity and net mapping one port at a time. Static tests expose assembly and wiring errors early, but they do not replace live-link testing.

Bring up each port before running concurrent traffic

Connect known-good PHY, RJ45 and cable paths to ports A through D and record negotiated rate and error counters. Then run sustained traffic on all four ports. A board that works one port at a time but loses speed or accumulates errors under concurrency needs checks around PHY power, reference planes, inter-port routing and local temperature before the transformer itself is blamed.

Apply the intended PoE load during the thermal test

When WHDG88409PG or WHDG96503PTG is used for PoE+, connect the planned PSE or PD circuit, cable and load. Operate every port that will carry power, wait for temperatures to stabilize, and record surface temperature, link state, error counters and hot-restart recovery. If port powers differ, rotate the high load among ports to expose uneven PCB copper or airflow.

7. Frequently Asked Questions about quad-port Gigabit LAN transformer selection

1. Can a 72-pin quad-port transformer directly replace an 88-pin product?

No. WHDG72303G uses a long 72-pin, 1.78 mm-pitch footprint. WHDG88403G and WHDG88409PG use block-style 88-pin, 1.65 mm-pitch footprints. Their hole patterns and body envelopes differ, so the mechanical drawing, schematic and PCB library must be reviewed as a new design branch.

2. Can non-PoE and PoE+ 88-pin products share one schematic?

Do not assume so from pin count or outline. WHDG88403G is non-PoE, while WHDG88409PG supports PoE+. Match the center taps and internal connections to each product schematic. A similar mechanical footprint does not guarantee that the electrical nets can be reused.

3. Does a 720 mA rating give the total power of a four-port switch?

No. The current capability helps define the magnetics selection range. Total system power also depends on the PSE or PD architecture, current per pair, supply voltage, cable drop, efficiency and thermal design. Validate temperature and link stability with the actual four-port load.

4. Can a 0 to 70 °C product be used in outdoor equipment below freezing?

Choose a product whose operating range covers the equipment requirement. WHDG96503PTG provides a -40 to +85 °C PoE+ branch. The PHY, RJ45 connector, power components and remaining parts must meet the same system-level temperature requirement.

5. What information helps VOOHU select a quad-port LAN transformer?

Provide the PHY model and reference circuit, the arrangement of four RJ45 connectors, the current PCB hole map or available space, PoE requirement, PSE or PD role, target ambient range, isolation requirement and assembly process. These details quickly show whether the 72-, 88- or 96-pin branch is the right starting point.

8. Conclusion

The 72-, 88- and 96-pin versions of a quad-port Gigabit LAN transformer represent different mechanical and electrical branches, not interchangeable numbers. WHDG72303G and WHDG88403G cover two non-PoE layout options, WHDG88409PG provides an 88-pin PoE+ option, and WHDG96503PTG provides a 96-pin wide-temperature PoE+ option. Define the hole pattern, four-port arrangement, power architecture and temperature range first, then complete pin-by-pin mapping and concurrent four-port testing. For help with an existing board,send the design requirements to VOOHU and request samples.