WHD40101G 10/100BASE-TX LAN Transformer

The WHD40101G holds eight 1CT:1CT units, split across four ports at two channels — one pairset — each.

A 100M link uses two differential pairs, one transmitting and one receiving, so each port takes two units, and four ports take eight. The count also works in reverse as a rate check: a quad-port Gigabit device holds sixteen units. A quad-port device with only eight units is a 100M part.

CMGND marks the common-mode ground node for each port: the WHD40101G drawing gives one per port on the cable side, with TCT1 through TCT4 as the corresponding chip-side centre taps.

The cable-side common-mode ground is where the termination network attaches — typically through a capacitor to chassis or reference ground — while the chip-side centre tap takes bias or a reference potential as the PHY reference design specifies. The two are brought out separately and named differently precisely to signal that they must not be tied into one net, which would defeat the isolation. Each of the four ports has its own set.

A 37.80 × 7.80 mm body, 11.20 mm Max high, on 1.78 mm pitch with a 33.82 mm span and 4.80 mm row spacing.

Leads are 3.00 mm with a recommended ø0.90 mm hole. The approval document for the WHD40101G specifies laser marking, which resists solvents and abrasion better than ink printing — the text survives wave soldering and cleaning, making incoming inspection and line traceability more reliable. The body is a long narrow bar, so the layout needs close to 38 mm of straight space. Other outlines sit in the 10/100 BASE-T range.

Four-port 100M equipment where the component temperature stays between 0 °C and +70 °C and the PCB can give a 40-pin through-hole layout about 38 mm long on 1.78 mm pitch.

Typical uses are small industrial switches, multi-port acquisition gateways and 100M line cards in rack equipment. The WHD40101G has no PoE capability, so all four ports are powered locally — the 8 mA in the datasheet is the DC bias used when measuring inductance, not current available for powering anything. Other port counts sit in the 10/100 BASE-T range.