Cortina Systems LXT9785 and
LXT9785E Advanced 8-Port 10/
100 Mbps PHY Transceivers
Datasheet
The Cortina Systems LXT9785 and LXT9785E are 8-port Fast Ethernet PHY Transceivers supporting
IEEE 802.3 physical layer applications at 10 Mbps and 100 Mbps. These devices provide Serial/Source
Synchronous Serial Media Independent Interfaces (SMII/SS-SMII) and Reduced Media Independent
Interface (RMII) for switching and other independent port applications. The LXT9785 and LXT9785E are
identical except for the IP telephony features included in the LXT9785E transceiver. The LXT9785E is an
enhanced version of the LXT9785 that detects Data Terminal Equipment (DTE) requiring power from the
switch over a CAT5 cable. The system uses the information collected by the LXT9785E to apply power if
the DTE at the far end requires power over the cable, such as an IP telephone.
Each network port can provide a twisted-pair (TP) or Low-Voltage Positive Emitter Coupled Logic
(LVPECL) interface. The twisted-pair interface supports 10 Mbps and 100 Mbps (10BASE-T and
100BASE-TX) Ethernet over twisted-pair. The LVPECL interface supports 100 Mbps (100BASE-FX)
Ethernet over fiber-optic media.
The LXT9785/LXT9785E provides three discrete LED driver outputs for each port. The devices support
both half-duplex and full-duplex operation at 10 Mbps and 100 Mbps and require only a single 2.5 V
power supply.
Applications
Product Features
Enterprise switches
IP telephony switches
Storage Area Networks
Multi-port Network Interface Cards (NICs)
Eight IEEE 802.3-compliant 10BASE-T or
100BASE-TX ports with integrated filters.
100BASE-FX fiber-optic capability on all ports.
2.5 V operation.
Low power consumption; 250 mW per port
typical.
Multiple RMII or SMII/SS-SMII ports for
independent PHY port operation.
Auto MDI/MDIX crossover capability.
Proprietary Optimal Signal Processing
architecture improves SNR by 3 dB over ideal
analog filters.
Optimized for dual-high stacked RJ-45
applications.
MDIO sectionalization into 2x4 or 1x8
configurations.
Supports both auto-negotiation systems and
legacy systems without auto-negotiation
capability.
Robust baseline wander correction.
Configurable through the MDIO port or external
control pins.
JTAG boundary scan.
208-pin PQFP: LXT9785HC, LXT9785EHC,
LXT9785HE.
241-ball BGA: LXT9785BC, LXT9785EBC.
196-ball BGA: LXT9785MBC (includes DTE
detection similar to the LXT9785E)
DTE detection for remote powering applications
(LXT9785E and LXT9785MBC only).
Extended temperature operation of -40 oC to
+85 oC (LXT9785E only).