1Gbps to 11.3Gbps, SFP+ Laser Driver with Laser Impedance Mismatch Tolerance

The MAX3946 is a +3.3V, multirate, low-power laser diode driver designed for Ethernet and Fibre Channel transmission systems at data rates up to 11.3Gbps. This device is optimized to drive a differential transmitter optical subassembly (TOSA) with a 25Ω flex circuit. The unique design of the output stage enables use of unmatched TOSAs, greatly reducing headroom limitations and lowering power consumption.

The device receives differential CML-compatible signals with on-chip line termination. It can deliver laser modulation current of up to 80mA, at an edge speed of 22ps (20% to 80%), into a 5Ω to 25Ω external differential load. The device is designed to have a symmetrical output stage with on-chip back terminations integrated into its outputs. A high-bandwidth, fully differential signal path is implemented to minimize deterministic jitter. An equalization block can be activated to compensate for the SFP+ connector. The integrated bias circuit provides programmable laser bias current up to 80mA. Both the laser bias generator and the laser modulator can be disabled from a single pin.

A 3-wire digital interface reduces the pin count and permits adjustment of input equalization, pulse-width adjustment, Tx polarity, Tx deemphasis, modulation current, and bias current without the need for external components. The MAX3946 is available in a 4mm x 4mm, 24-pin TQFN package.

Applications

* 10GBASE-LR SFP+ Optical Transceivers * 10GBASE-LRM SFP+ Optical Transceivers * 10GFC SFP+ Optical Transceivers * 4x/8x FC SFP+ Optical Transceivers * OC192-SR XFP/SFP+ SDH/SONET Transceivers

* 225mW Power Dissipation Enables < 1W SFP+ Modules

* Up to 100mW Power Consumption Reduction by Enabling the Use of Unmatched FP/DFB TOSAs

* Supports SFF-8431 SFP+ MSA and SFF-8472 Digital Diagnostic

* 225mW Power Dissipation at 3.3V (IMOD = 40mA, IBIAS = 60mA Assuming 25Ω TOSA)

* Single +3.3V Power Supply

* Up to 11.3Gbps (NRZ) Operation

* Programmable Modulation Current from 10mA to 100mA (5Ω Load)

* Programmable Bias Current from 5mA to 80mA

* Programmable Input Equalization

* Programmable Output Deemphasis

* 25Ω Output Back Termination at TOUT+ and TOUT-

* DJ Performance 7psP-P with Mismatched Differential Load (5Ω)

* DJ Performance 5psP-P with Mismatched Differential Load (25Ω)

* DJ Performance 5psP-P with 50Ω Differential Load

* Programmable Pulse Width

* Edge Transition Times of 22ps

* Bias Current Monitor

* Integrated Eye Safety Features

* 3-Wire Digital Interface

* -40°C to +95°C Operation