HX1188FNL

The Pulse Electronics HX1188FNL is a single-port 100Base-TX Ethernet transformer/choke designed for Local Area Network (LAN) applications. It provides the necessary impedance matching, signal coupling, and electrical isolation between the Ethernet PHY transceiver and the RJ-45 connector. The device features a center-tapped 1:1 turns ratio for both transmit and receive channels, with 350uH open-circuit inductance measured at 100kHz with 8mA DC bias. The transformer provides 1500Vrms isolation voltage and meets all IEEE 802.3 electrical specifications for 100Base-TX operation. With crosstalk performance of -62dB minimum and common-mode rejection of -32dB typical, it ensures reliable signal integrity in noisy environments. The 16-terminal gull-wing SMD package enables automated pick-and-place assembly.

The HX1188FNL operates as a signal coupling and isolation transformer for 100Base-TX Ethernet: 1) Impedance Matching: The 1:1 turns ratio transformers match the impedance between the PHY transceiver (100Ohm differential) and the twisted-pair cable (100Ohm characteristic impedance), minimizing signal reflections. 2) Galvanic Isolation: The transformer provides 1500Vrms electrical isolation between the Ethernet controller side and the cable side, protecting equipment from ground loops, common-mode voltages, and transient events per IEEE 802.3 requirements. 3) Common-Mode Rejection: The center-tapped windings allow connection of Bob Smith termination resistors (75Ohm to ground via high-voltage capacitors) that absorb common-mode noise, improving EMI performance. 4) Signal Coupling: The transformer magnetically couples the differential transmit and receive signals between the PHY and the cable, passing the high-frequency data signals while blocking DC and low-frequency common-mode interference.

• 100Base-TX Ethernet PHY to RJ-45 interface in embedded systems
• LAN on motherboard (LOM) designs for desktop and server platforms
• Network interface cards (NIC) for 100Mbps Ethernet
• Industrial Ethernet equipment requiring galvanic isolation
• Set-top boxes and IoT gateways with Ethernet connectivity