Analog Devices Inc./Maxim Integrated DS1856B-020

Overview

DS1856B-020 from Maxim Integrated is a dual, temperature-controlled, nonvolatile variable resistor IC with integrated 12-bit analog monitoring (VCC, MON1–MON3, internal temperature), password-protected EEPROM, and SFF-8472-compliant diagnostics. It delivers two 256-position linear resistors (20kΩ/20kΩ), ±3°C thermometer accuracy, and 2-wire serial interface for optical transceiver bias control and real-time thermal compensation.

For engineers reviewing the DS1856B-020 datasheet, DS1856B-020 pinout, DS1856B-020 application, or DS1856B-020 equivalent, this device serves as a drop-in upgrade path from DS1852/DS1859 in SFF-8472-compliant modules requiring calibrated analog monitoring, secure resistor programming, and temperature-indexed lookup tables across –40°C to +95°C.

Technical Context

The DS1856B-020 implements a dual-resistor architecture where each 20kΩ resistor is controlled via a temperature-addressed 72-byte lookup table (00h–C7h), enabling independent resistance assignment every 2°C from –40°C to +102°C. Resistor positions are stored in EEPROM and retain settings after power cycle.

Its analog subsystem integrates a 12-bit ADC with factory-calibrated full-scale ranges (2.5V for MON inputs, 6.5536V for VCC), alarm/warning flags per channel, and automatic round-robin conversion every 47–60ms. The 2-wire interface supports standard (100kHz) and fast (400kHz) modes with programmable slave addresses (A2h default, configurable via ADFIX).

Key Specifications

Availability

DS1856B-020 is available at Aetrix Electronics and suitable for optical transceivers, RF power amplifier bias control, and industrial instrumentation requiring stable component supply, long-term calibration retention, and SFF-8472 compliance.

Supply support for DS1856B-020 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, mixed-signal, and digital ICs for communications, computing, and industrial applications.

The DS1856B-020 belongs to Maxim's optical monitoring and control product line, engineered specifically for SFF-8472-compliant pluggable transceivers needing integrated temperature-compensated resistors, multi-channel analog monitoring, and secure configuration storage.

FAQ

What is the resistor value and tolerance of DS1856B-020 at 25°C?

The DS1856B-020 features two 20kΩ nonvolatile variable resistors. At TA = +25°C, Position 00h resistance is 0.20–0.55kΩ and Position FFh is 15–25kΩ. Absolute linearity is ±2 LSB, and temperature coefficient is 50 ppm/°C - ensuring stable biasing over temperature in optical modules.

Does DS1856B-020 support SFF-8472 compliance out of the box?

Yes, DS1856B-020 is explicitly designed for SFF-8472 compatibility. It provides five monitored channels (temperature, VCC, MON1–MON3), alarm/warning flags, Tx fault and LOS outputs (OUT1/OUT2), and memory-mapped registers aligned with SFF-8472 Table 4–11 - enabling direct integration into GBIC/SFP modules without external logic.

How does the temperature-controlled resistor function work in DS1856B-020?

The DS1856B-020 uses an internal direct-to-digital temperature sensor to index into two 72-byte lookup tables (one per resistor). Each table entry corresponds to a 2°C increment from –40°C to +102°C, allowing independent resistor position (00h–FFh) assignment per temperature bin - enabling precise thermal compensation of laser bias and modulation currents.

What security levels does DS1856B-020 offer, and how are they enforced?

DS1856B-020 implements three-tier password protection: User (read-only monitoring), Level 1 (read/write customer data tables), and Level 2 (full access including PW1/PW2 programming). Passwords are entered into PWE bytes (7Bh–7Eh); PW1 and PW2 are stored in protected EEPROM (B0h–B7h) and never readable - preventing unauthorized reconfiguration of critical optical parameters.

What package type and pin count does DS1856B-020 use?

DS1856B-020 is housed in a 16-ball CSBGA package (4mm × 4mm, 1.0mm pitch), identical in footprint to the DS1856E-020 TSSOP variant. Pinout includes dual resistor terminals (L0/H0, L1/H1), three analog monitor inputs (MON1–MON3), 2-wire interface (SDA/SCL), dual open-drain buffers (OUT1/OUT2), and dedicated VCC/GND - optimized for high-density optical module PCB layouts.