Analog Devices Inc./Maxim Integrated DS1875T+

Overview

DS1875T+ from Maxim Integrated is a PON triplexer and SFP controller IC designed for burst-mode optical transceivers. It integrates laser bias/modulation control, APD bias generation via PWM, 10-channel analog monitoring (including internal temperature sensor), four DAC outputs, and full SFF-8472 diagnostics. It enables compliant BPON/GPON/EPON triplexer modules with eye-safety shutdown and APC loop functionality.

For engineers reviewing the DS1875T+ datasheet, DS1875T+ pinout, DS1875T+ application, or DS1875T+ equivalent, this device supports critical timing-critical burst-mode operation in SFP/SFP+ modules, provides factory-calibrated RSSI (29dB electrical dynamic range), and delivers programmable APD bias up to 90V using its integrated PWM controller with selectable switching frequencies (131–1050 kHz).

Technical Context

The DS1875T+ implements closed-loop APC using BMD input feedback and temperature-indexed LUTs for both bias and modulation current control. Its dual-range RSSI circuit supports enhanced signal monitoring across varying optical power levels, while the 13-bit ADC with programmable full-scale ranges (e.g., MON3 fine resolution of 312.5 µV) enables precise analog sensing of APD, laser, and supply parameters.

Its I²C interface (400 kHz fast-mode compatible) manages configuration, fault reporting, and nonvolatile memory (120 + 128 + 256 bytes across protected address spaces). The PWM controller operates in boost or buck mode with compensation pin (COMP), feedback pin (FB), and dedicated BIAS/MOD outputs synchronized to transmit enable (TX-D) timing with sub-5 µs turn-on/off delays.

Key Specifications

Pinout & Package

DS1875T+ is housed in a 38-pin TQFN package (5 mm × 7 mm × 0.8 mm) with exposed pad (EP) for thermal dissipation. Pin functions are validated per Maxim's DS1875 datasheet Rev 1 (10/08), Figure "Pin Configuration" and "Pin Description" (p.13).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PON triplexer and SFP controller applications.

Compared with MAX3643, DS1875T+ provides full-system integration (monitoring, control, diagnostics), while DS1878 extends operational reliability at higher ambient temperatures without altering layout or software architecture.

Availability

DS1875T+ is available at Aetrix Electronics and suitable for BPON/GPON triplexers, SFP transceiver modules, and APD-based optical receivers requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for DS1875T+ 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 precision analog, mixed-signal, and power management solutions for communications, computing, and industrial markets.

The DS1875T+ belongs to Maxim's optical networking product line, engineered specifically to consolidate burst-mode control, APD biasing, and SFF-8472 compliance into a single IC for cost-sensitive, high-volume PON and SFP modules.

FAQ

What is the primary function of the DS1875T+ in an optical transceiver?

The DS1875T+ serves as a fully integrated PON triplexer and SFP controller, providing laser bias and modulation control via APC loops, APD bias generation using its PWM controller, 10-channel analog monitoring (including internal temperature), four DAC outputs, and complete SFF-8472 diagnostic compliance. It replaces multiple discrete components in burst-mode optical modules.

Does the DS1875T+ support both boost and buck configurations for APD bias generation?

Yes, the DS1875T+ PWM controller supports both boost and buck topologies. In boost mode, it can generate up to 90 V APD bias using optional external components (inductor, diode, FET); in buck mode, it regulates lower-voltage bias supplies. Selection is determined by external circuit configuration-not internal register setting.

How does the DS1875T+ ensure laser eye safety compliance?

The DS1875T+ ensures eye safety through hardware-enforced shutdown: the FETG output drives an external FET to cut APD/laser power within 5 µs upon detecting overcurrent, temperature violation, or loss-of-signal (LOSI). TX-F asserts simultaneously, and safety thresholds are stored in password-protected memory to prevent tampering.

What are the key timing specifications for burst-mode operation in the DS1875T+?

The DS1875T+ meets all PON burst-timing requirements: BEN high time ≥400 ns, first BMD sample within 400 ns of BEN assertion, BIAS/MOD turn-on/off delay ≤5 µs, and TX-F assertion ≤5 µs after fault detection. These are guaranteed across −40°C to +95°C and 2.85–3.9 V supply range.

Can the DS1875T+ be used in SFP+ modules, or is it limited to SFP?

The DS1875T+ is qualified for SFP modules per SFF-8472 and supports GPON/BPON burst-mode timing, but it is not rated for SFP+ data rates (up to 10.3125 Gbps). Its analog monitoring bandwidth and control loop latency are optimized for 1.25–2.5 Gbps PON applications-not 10G Ethernet physical layer requirements.