General Description

The MAX3948 is a 3.3V, multirate, low-power laser diode driver designed for Ethernet, Fibre Channel, and SONET transmission systems at data rates up to 11.3Gbps. This device is optimized to drive a differential transmitter optical subassembly (TOSA) with a 25I flex circuit. The unique design of the output stage enables DC-coupling to unmatched TOSAs, thereby lowering transmitter power consumption by more than 100mW.

The MAX3948 receives differential AC-coupled signals with on-chip termination. It can deliver laser modulation currents of up to 85mA at an edge speed of 26ps (20 to 80) into a 5I external differential load. The device is designed to have a high-bandwidth differential signal path with on-chip back termination resistors integrated into its outputs. An input equalization block can be activated to compensate for SFP+/QSFP+ host connector losses. The integrated DC circuit provides programmable laser DC currents up to 61mA. Both the laser DC current generator and the laser modulator can be disabled from a single pin.

The device offers one dedicated pin (VSEL) to program up to four channel addresses for multichannel applications.

The use of a 3-wire digital interface reduces the pin count while permitting adjustment of input equalization, polarity, output deemphasis, and modulation and DC currents without the need for external components. The MAX3948 is available in a 3mm x 3mm, 16-pin TQFN package, and is specified for the -40NC to +95NC extended temperature range.

Benefits and Features

♦ Lowest Power Consumption

   ◇ 168mW Typical IC Power Dissipation at 3.3V

        (LDMOD = 40mA, LDDC = 20mA)

   ◇ 383mW Total Transmitter Power Dissipation at

        3.3V Including LDMOD = 40mA, LDDC = 20mA

   ◇ Enables < 1W Maximum Total SFP+ Module

        Power Dissipation

   ◇ Enables < 2.5W Maximum Total QSFP+ Module

        Power Dissipation

♦ Saves Board Space

   ◇ Small 3mm x 3mm Package

   ◇ DC-Coupling to the Laser Reduces External

        Component Count

♦ Flexibility

   ◇ Operate Up to Four MAX3948 ICs Over Single

        3-Wire Digital Interface

   ◇ Programmable Modulation Current Up to

        85mA (5ω Load)

   ◇ Programmable DC Current Up to 61mA

        (Translates to Up to 100mA Laser Bias Current)

   ◇ Programmable Input Equalization and Output

        Deemphasis

♦ Safety

   ◇ Supports SFF-8431 SFP+ MSA and SFF-8472

        Digital Diagnostic

   ◇ Integrated Eye Safety Features with Maskable

        Faults

   ◇ DC Current Monitor

Applications

   40GBASE-LR4 QSFP+ Optical Transceivers

   10GBASE-LR SFP+ Optical Transceivers

   10GBASE-LRM SFP+ Optical Transceivers

   OC192-SR SFP+ SDH/SONET Transceivers