Renesas HXT44400-DNU/C

Overview

HXT44400-DNU/C from Renesas Electronics is a quad-channel linear PAM4 directly-modulated laser (DML) driver for 200G LR optical modules, supporting 28 GBaud / 56 Gbps PAM4 signaling, 410 mW per-channel power dissipation, IMOD up to 60 mA_PP, and IBIAS up to 60 mA at V_CC = 2.8 V, deployed in datacenter interconnects with DC-coupled TOSA integration.

For engineers reviewing the HXT44400-DNU/C datasheet, HXT44400-DNU/C pinout, HXT44400-DNU/C application, or HXT44400-DNU/C equivalent, key selection criteria include PAM4 linearity, integrated 12-bit ADC with 6-channel MUX, programmable 8-bit laser bias/modulation control, APC capability, and 2-wire I²C interface compliance for QSFP56 module telemetry and calibration.

Technical Context

The HXT44400-DNU/C implements a linear gain-adjustable pre-driver architecture with CTLE equalization (4-bit programmable), polarity inversion, and eye-shaping control (8-bit GAIN), enabling precise analog modulation of DMLs without digital predistortion. Each channel includes independent bias and modulation current DACs, laser safety logic, and fault detection via V_FAIL sense and TX_FAULT assertion.

It integrates dual temperature sensing (internal TSENSP/TSENSN and external T_SENSE_EXT), RSSI-based receive optical power monitoring via dedicated I-V converter, and automatic power control using closed-loop feedback through the 12-bit ADC and OTP-calibrated registers-all coordinated over a configurable 2-wire slave interface with interrupt masking and reset management.

Key Specifications

Pinout & Package

HXT44400-DNU/C is supplied as a bare die (nominal size 1350 × 3320 μm) intended for direct integration into TOSA packages; no leaded or surface-mount package is assigned. Pin definitions are defined by wafer-level bump map per functional block diagram (Figure 1).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar linear PAM4 DML driver applications.

Compared with MAX3999AETL+T and SiPh1000-DML-DRV, the HXT44400-DNU/C uniquely delivers quad-channel 56G PAM4 linearity, full APC telemetry, and field-programmable 2-wire control in a TOSA-optimized die form-making it the only option meeting QSFP56 LR production requirements for 200G datacenter optics.

Availability

HXT44400-DNU/C is available at Aetrix Electronics and suitable for 200G QSFP56 LR Ethernet modules, Fibre Channel Gen6 transceivers, and InfiniBand EDR optical links requiring stable component supply, calibrated bare-die integration, and long-term lifecycle support.

Supply support for HXT44400-DNU/C 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

Renesas Electronics Corporation is a global semiconductor leader delivering microcontrollers, analog, power, and connectivity solutions for automotive, industrial, infrastructure, and IoT applications.

The HXT44400-DNU/C belongs to Renesas' high-speed optical interconnect product line, engineered specifically for PAM4-based 200G/400G pluggable modules requiring linear drive fidelity, on-die diagnostics, and TOSA-level integration efficiency.

FAQ

What is the primary function of the HXT44400-DNU/C in optical modules?

The HXT44400-DNU/C serves as a quad-channel linear PAM4 DML driver that performs electrical-to-optical conversion by precisely controlling laser bias and modulation currents. It integrates APC, temperature sensing, RSSI-based receive power monitoring, and 2-wire configurability-enabling full telemetry and closed-loop control within 200G QSFP56 LR modules. The HXT44400-DNU/C replaces multiple discrete drivers and monitoring ICs in TOSA assemblies.

Does the HXT44400-DNU/C support PAM4 signaling natively, or does it require external DSP?

The HXT44400-DNU/C supports native linear PAM4 modulation without external DSP. Its analog pre-driver architecture-including CTLE, gain adjustment, and polarity inversion-is optimized for 28 GBaud PAM4 waveforms. Linearity is maintained via factory-trimmed DACs and OTP calibration, eliminating need for digital predistortion. The HXT44400-DNU/C delivers <4% THD at full 60 mA_PP swing, satisfying IEEE 802.3cd PAM4 linearity requirements.

How is temperature managed in the HXT44400-DNU/C for APC stability?

The HXT44400-DNU/C uses dual temperature sensing: an internal differential pair (TSENSP/TSENSN) monitors die junction temperature, while T_SENSE_EXT accepts an external thermistor for module housing measurement. Both inputs feed the integrated 12-bit ADC, enabling real-time APC compensation across –5°C to +95°C. The HXT44400-DNU/C applies OTP-stored thermal coefficients to maintain optical power stability within ±0.5 dB over temperature-critical for GR-468 qualification.

Can the HXT44400-DNU/C be used in NRZ-based modules, or is it strictly for PAM4?

The HXT44400-DNU/C is optimized for PAM4 but remains functional in NRZ mode. Its linear architecture supports 25–28 GBaud NRZ with reduced equalization overhead and lower power vs. dedicated NRZ drivers. However, features like 4-bit EQ control and eye shaping are tuned for PAM4; NRZ users must validate jitter and rise/fall symmetry. The HXT44400-DNU/C retains full APC, monitoring, and I²C functionality in NRZ configurations.

What packaging form is supplied for the HXT44400-DNU/C, and how is it mounted?

The HXT44400-DNU/C is delivered as a bare die (1350 × 3320 μm) with wafer-level bumps, intended for flip-chip or wire-bond mounting directly into TOSA housings. It has no standard IC package-no QFN, BGA, or leaded variant exists. Mounting requires controlled atmosphere die attach, impedance-matched RF routing, and thermal vias to the TOSA baseplate. The HXT44400-DNU/C's DC-coupled design eliminates AC coupling capacitors, improving RF integrity in high-density optical subassemblies.