Analog Devices Inc./Maxim Integrated MAX3268CUB

Overview

MAX3268CUB from Maxim Integrated is a 1.25Gbps PECL-output limiting amplifier for optical receiver front-ends, featuring programmable loss-of-signal (LOS) detection with RTH-set thresholds (e.g., 2.20–4.8mV low-level assert), 11ps deterministic jitter, 100–150ps edge speed, and operation from +3.0V to +5.5V supply. It serves as the final gain stage in Gigabit Ethernet and Fibre Channel receivers following transimpedance amplifiers like MAX3266/MAX3267.

For engineers reviewing the MAX3268CUB datasheet, MAX3268CUB pinout, MAX3268CUB application, or MAX3268CUB equivalent, key selection criteria include its 10-pin µMAX-EP package, PECL output compatibility (VCC − 2V termination), LOS hysteresis (2.2–4.4dB), input-referred noise (150µVRMS), and absence of external SQUELCH control (internally unconnected).

Technical Context

The MAX3268CUB implements a multistage limiting amplifier with 55dB total gain and integrated RMS power detection. Its offset-correction loop uses CAZ1/CAZ2 pins to stabilize DC operating points, minimizing deterministic jitter caused by sub-100µV input offsets.

It delivers standards-compliant PECL outputs (−1.025V to −0.880V high, −1.810V to −1.620V low, referenced to VCC) with 4Ω single-ended output resistance and supports AC-coupled transmission-line interfaces. The device lacks external SQUELCH control-functionally disabled per pin configuration-and relies on internal LOS assertion logic driven by TH-resistor programming.

Key Specifications

Pinout & Package

MAX3268CUB is housed in a 10-pin µMAX-EP package (3.0mm × 3.0mm, 0.6mm height) with exposed paddle soldered to PCB ground for thermal management.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar limiting amplifier applications.

Compared with MAX3268CUE and MAX3768CUB, the MAX3268CUB offers identical performance in a compact µMAX package at commercial temperature grade-ideal for cost-sensitive, space-constrained SFF optical modules where extended temperature is unnecessary.

Availability

MAX3268CUB is available at Aetrix Electronics and suitable for Gigabit Ethernet optical receivers, Fibre Channel 1x receivers, and small-form-factor transceivers requiring stable component supply, consistent lead-free µMAX-EP packaging, and guaranteed commercial-temperature performance.

Supply support for MAX3268CUB 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) designs precision analog and mixed-signal ICs for communications, computing, and industrial applications.

The MAX3268CUB belongs to Maxim's high-speed limiting amplifier product line, engineered specifically for optical receiver front-ends in datacom and storage networks demanding low jitter, programmable LOS, and PECL compatibility.

FAQ

What is the operating temperature range for the MAX3268CUB?

The MAX3268CUB is specified for operation from 0°C to +70°C ambient temperature. This commercial-grade range aligns with typical SFP and GBIC module environments. For extended-temperature applications, consider the pin-compatible MAX3768CUB, which operates from −40°C to +85°C while retaining identical electrical performance and µMAX-EP packaging.

Does the MAX3268CUB support squelch functionality?

No, the MAX3268CUB does not support external squelch control. Per the datasheet pin description, the SQUELCH pin is internally unconnected in the 10-pin µMAX variants (including MAX3268CUB). Squelch is only available on MAX3264/MAX3265 TSSOP versions and MAX3765/MAX3768 devices where it is internally tied to VCC.

How is loss-of-signal (LOS) threshold set on the MAX3268CUB?

The LOS threshold on the MAX3268CUB is programmed using an external resistor (RTH) connected between the TH pin and ground. The datasheet provides curves showing LOS assert level versus RTH value-e.g., 2.5kΩ yields ~2.20–4.8mV low-level assert, while 20kΩ yields ~18.0–41.5mV high-level assert. Hysteresis is fixed at 2.2–4.4dB across all settings.

What termination is required for the PECL outputs of the MAX3268CUB?

The MAX3268CUB PECL outputs (OUT+, OUT−) require termination to VCC − 2V using two 50Ω resistors-one from each output to VCC − 2V-as shown in Figure 1(c) of the datasheet. This standard PECL biasing ensures correct logic levels (−1.025V to −0.880V high, −1.810V to −1.620V low) and optimal signal integrity.

Can the MAX3268CUB be used with CML-output systems?

No, the MAX3268CUB provides PECL-compatible outputs only. CML output capability is exclusive to the MAX3264/MAX3265/MAX3765 family members. Attempting to interface MAX3268CUB outputs with CML receivers will result in incompatible voltage levels and potential signal integrity failure. Use MAX3265CUB for CML output in the same µMAX package.