MAX3969E/D

Overview

The MAX3969 is a limiting amplifier with PECL data outputs designed for low-cost fiber optic receivers in ATM, Fast Ethernet, FDDI, and ESCON applications. It features 1mV P-P input sensitivity and an integrated power detector providing an analog RSSI output. The device includes TTL LOS and PECL SD outputs with programmable thresholds down to 2.7mV P-P. An optional squelch function holds data outputs at known states when signals fall below the threshold. Available in a 20-pin Thin QFN package or die form, it operates over -40°C to +85°C.

Feature Summary

• Integrated power detector provides analog received-signal-strength indicator
• Programmable loss-of-signal threshold with complementary TTL and PECL outputs
• Optional squelch function disables data switching during signal loss
• Compatible with 4B/5B data coding standards

Applications

• SFP/SFF Transceivers
• Fast Ethernet/FDDI Transceivers
• 155Mbps LAN ATM Transceivers
• ESCON Receivers
• FTTx Transceivers

Procurement Notes

Verify the specific ordering suffix to confirm package type and temperature range. The MAX3969ETP is available in a 20-pin Thin QFN package for commercial temperatures, while dice are offered for higher junction temperature ranges but tested only at ambient room temperature. Ensure compatibility with host board voltage levels and termination requirements for PECL outputs before procurement.

Selection Notes

Select the MAX3969 for applications requiring high sensitivity and diagnostic monitoring capabilities. The device supports AC-coupled inputs and requires external capacitors for offset correction and filtering. Consider the exposed pad requirement for thermal management in the QFN package. Verify that the host system can accommodate the required pull-up resistors for TTL outputs and proper termination for PECL interfaces.

Part Context

This component belongs to Maxim Integrated's family of limiting amplifiers optimized for optical receiver front-ends. It integrates gain stages, offset correction, and signal detection into a single compact solution. The design targets cost-sensitive multi-gigabit serial communication links where reliable signal detection and strength monitoring are critical for network performance and maintenance.

Replacement Considerations

No official substitute part numbers are confirmed in the datasheet.

FAQ

How is the power-detect threshold programmed?

The threshold is set using two external resistors, R1 and R2, connected between VTH, INV, and ground. R1 is typically 100kΩ, and R2 determines the trip point based on the Power-Detect Threshold vs. R2 graph.

What is the purpose of the SQUELCH pin?

Connecting SQUELCH to VCC enables the squelch function, which forces OUT- low and OUT+ high when the input signal falls below the programmed threshold, preventing downstream devices from responding to noise.

How should the PECL outputs be terminated?

The PECL outputs (OUT+, OUT-, SD) should be terminated with 50Ω to (VCC - 2V) for proper operation, although other standard termination techniques may be used.