Analog Devices Inc./Maxim Integrated MAX3946ETG+T

Overview

MAX3946ETG+T from Maxim Integrated is a +3.3V, multirate SFP+ laser driver IC optimized for 1Gbps to 11.3Gbps Ethernet and Fibre Channel optical transceivers. It drives differential TOSAs with 5Ω–50Ω loads, delivers up to 80mA modulation current (22ps edge speed), integrates programmable bias (5–80mA) and modulation DACs, and features on-chip 25Ω back-termination at TOUT+/TOUT− for SFP+ compliance.

For engineers reviewing the MAX3946ETG+T datasheet, MAX3946ETG+T pinout, MAX3946ETG+T application, or MAX3946ETG+T equivalent, this page provides verified technical context, deterministic jitter performance (5ps_P-P @ 25Ω), SFF-8431/8472 compliance, 3-wire digital interface control, and real-world SFP+ module design constraints including laser impedance mismatch tolerance and eye safety circuitry.

Technical Context

The MAX3946ETG+T implements a fully differential, high-bandwidth signal path with integrated input equalization (programmable via SET_TXEQ register) and output deemphasis (controlled by TXDE_MD[1:0] and SET_TXDE[5:0]) to compensate for SFP+ connector losses and channel attenuation. Its symmetrical output stage includes on-chip 25Ω back terminations at both TOUT+ and TOUT−, enabling stable operation into unmatched FP/DFB TOSAs without external termination.

It integrates dual 9-bit DACs - one for laser bias current (SET_IBIAS, 5–80mA range, ±0.5%FS INL) and one for modulation current (SET_IMOD, 10–80mA into 25Ω, ±1%FS INL) - both controllable via a 3-wire serial interface (SDA/SCL/CSEL). Fault detection includes HARD FAULT latching (via BMAX/BMON comparators) and SOFT FAULT warning registers (TXSTAT1/TXSTAT2).

Key Specifications

Pinout & Package

MAX3946ETG+T is housed in a 4mm × 4mm, 24-pin TQFN-EP package with exposed pad (EP) soldered to ground for thermal and electrical integrity. Pin count and layout comply with SFP+ MSA mechanical specifications.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar SFP+ laser driver applications.

Compared with MAX3946ETG+T, MAX3947ETG+T offers higher speed and drive strength but omits critical eye safety circuitry, while TLK10232IRCP adds CDR capability at the cost of pin compatibility and integrated bias control - making MAX3946ETG+T the optimal choice for standard SFP+ MSA-compliant, safety-certified 10G optical modules.

Availability

MAX3946ETG+T is available at Aetrix Electronics and suitable for 10GBASE-LR/LRM optical transceivers, 4x/8x Fibre Channel SFP+ modules, and OC192-SR SONET/SDH applications requiring stable component supply, SFP+ MSA compliance, and laser safety certification.

Supply support for MAX3946ETG+T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in high-performance analog, mixed-signal, and RF solutions for communications, computing, and industrial markets.

The MAX3946 product line is designed specifically for SFP+ optical transceiver modules, delivering low-power, multirate laser driving with integrated safety, diagnostics, and channel compensation to meet MSA and IEEE standards.

FAQ

What is the maximum data rate supported by the MAX3946ETG+T?

The MAX3946ETG+T supports data rates from 1Gbps up to 11.3Gbps NRZ, fully covering SFP+ MSA requirements for 10GBASE-LR, 10GBASE-LRM, and 4x/8x Fibre Channel. Its deterministic jitter remains ≤5ps_P-P at 11.3Gbps into a 25Ω differential load, ensuring compliance with IEEE 802.3ae and FC-PI-4 specifications. The MAX3946ETG+T is not rated for 12.5Gbps CPRI applications - that requires the MAX3947ETG+T variant.

Does the MAX3946ETG+T include integrated laser safety features?

Yes, the MAX3946ETG+T includes hardware-enforced eye safety circuitry. It uses dedicated pins (BMAX and BMON) to monitor laser bias current in real time: BMAX compares a resistor-divider voltage against an internal 1.2V bandgap reference, triggering a latched HARD FAULT if exceeded; BMON provides a 1/100× scaled current output for external monitoring. These features satisfy IEC 60825-1 Class 1 laser safety requirements when implemented per datasheet guidelines.

How is the modulation current programmed on the MAX3946ETG+T?

The MAX3946ETG+T uses a 9-bit digital-to-analog converter (DAC) controlled via its 3-wire serial interface to set modulation current from 10mA to 80mA_P-P into a 25Ω load. The upper 8 bits are written to the SET_IMOD[8:1] register during initialization; the LSB is updated via MODINC for fine-grained, safe adjustment. The IMODMAX register enforces a hardware current limit (up to 96mA) to protect the laser diode from overcurrent conditions.

What package type and thermal characteristics does the MAX3946ETG+T have?

The MAX3946ETG+T is packaged in a 4mm × 4mm, 24-pin TQFN-EP (exposed pad) package. Its junction-to-ambient thermal resistance (θ_JA) is 36°C/W on a 4-layer JEDEC-standard board, and junction-to-case (θ_JC) is 3°C/W. The exposed pad must be soldered to a solid ground plane to achieve specified thermal performance and ensure reliable operation at full 225mW dissipation across –40°C to +85°C ambient.

Is the MAX3946ETG+T compatible with SFF-8472 digital diagnostics?

Yes, the MAX3946ETG+T supports SFF-8472 Digital Diagnostic Monitoring (DDM) through its 3-wire interface and integrated registers. It provides real-time readback of bias current (via BMON scaling), modulation current (via DAC settings), supply voltage, and temperature (when used with external sensor). Fault status (TXSTAT1/TXSTAT2) and warning flags (e.g., IBIASERR, IMODERR) are accessible via the same interface, enabling full SFP+ MSA-compliant DDM implementation.