Analog Devices Inc./Maxim Integrated DS1857B-050+

Overview

DS1857B-050+ from Maxim Integrated is a dual nonvolatile temperature-controlled digital potentiometer with external temperature sensing (LM50-compatible), two analog monitor inputs (MON1/MON2), and 2-wire serial interface. It integrates two 50kΩ, 256-position linear variable resistors whose values are automatically adjusted every 2°C across –40°C to +102°C, enabling precise laser bias and modulation control in optical transceivers.

For engineers reviewing the DS1857B-050+ datasheet, DS1857B-050+ pinout, DS1857B-050+ application, or DS1857B-050+ equivalent, this device supports SFF-8472-compliant diagnostic monitoring, resistor disable via RHIZ, EEPROM-stored look-up tables, and simultaneous VCC/temperature/analog channel measurement with alarm flagging - critical for optical module calibration and production test.

Technical Context

The DS1857B-050+ implements a temperature-indexed dual-resistor architecture where each 50kΩ resistor's wiper position is selected from a 72-byte EEPROM look-up table addressed by digitized EXTTMP input (12-bit ADC, 625µV resolution, LM50 scale: +10mV/°C + 500mV offset). The device performs round-robin analog monitoring of VCC, MON1, MON2, and temperature at 20–30ms frame rate, with 16-bit left-justified results and user-configurable high/low limits.

Its 2-wire interface supports standard (100kHz) and fast (400kHz) modes, with three address pins (A0–A2) enabling up to 128 devices on one bus. Memory partitioning includes SRAM (60h–7Fh), protected EEPROM (00h–7Fh), and configurable main/auxiliary device addressing (ADEN/ADFIX bits), allowing flexible integration in multi-device SFP/SFF modules.

Key Specifications

Pinout & Package

DS1857B-050+ uses a 16-ball CSBGA package (4mm × 4mm, 1.0mm pitch), optimized for space-constrained optical transceiver modules.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual temperature-compensated resistor applications.

Compared with MAX5477EUB+ and AD5272BRMZ-50, the DS1857B-050+ uniquely integrates dual temperature-compensated resistors, four-channel analog monitoring, and SFF-8472 compliance in one 4mm × 4mm package - eliminating discrete sensor, ADC, and I²C logic required by alternatives.

Availability

DS1857B-050+ is available at Aetrix Electronics and suitable for optical transceivers, RF power amplifiers, and industrial instrumentation requiring stable component supply, calibrated temperature compensation, and SFF-8472 compliance.

Supply support for DS1857B-050+ 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, with emphasis on high-reliability, low-power, and standards-compliant solutions.

The DS1857B-050+ belongs to Maxim's optical module monitoring and control product line, engineered specifically for SFF-8472 and SFP MSA compliance in pluggable transceivers - delivering integrated temperature compensation, diagnostics, and nonvolatile configuration in minimal footprint.

FAQ

What is the function of the RHIZ pin on the DS1857B-050+?

The RHIZ pin on the DS1857B-050+ is a resistor disable input that places both 50kΩ digital potentiometers into a high-impedance (open-circuit) state when driven high. This feature directly supports SFF-8472 Tx Disable functionality, allowing safe, hardware-controlled shutdown of laser bias paths without software intervention. An internal 40–100kΩ pullup ensures default-on operation unless explicitly asserted.

How does the DS1857B-050+ interface with an external LM50 temperature sensor?

The DS1857B-050+ interfaces with the LM50 via its EXTTMP pin (Ball C4), which accepts the LM50's analog output (0.5V at 0°C, +10mV/°C). The device digitizes this voltage using a 12-bit ADC with 625µV resolution and maps the result to temperature-indexed resistor look-up tables - enabling automatic 2°C-step resistor value updates without host processor involvement.

Can the DS1857B-050+ operate from a 3.3V supply?

Yes, the DS1857B-050+ operates from a 3.0V to 5.5V supply, fully supporting 3.3V systems. Its I²C interface, analog monitors, and resistor terminals are specified across this range, and internal voltage references (e.g., 2.5V full-scale for MON1/MON2) remain stable. Decoupling with a 0.1µF capacitor at the VCC pin is required for noise immunity in 3.3V optical module designs.

What memory protection mechanisms does the DS1857B-050+ provide?

The DS1857B-050+ implements three-tiered write protection: (1) hardware-level via the WPEN pin (ground = writable, high = locked), (2) EEPROM-configurable via MPEN/APEN bits in register 89h for main/auxiliary device addresses, and (3) volatile SRAM (60h–7Fh) remains unprotected for runtime flag clearing. This prevents accidental or unauthorized modification of calibration data while allowing controlled field updates.

Does the DS1857B-050+ support multiple devices on the same I²C bus?

Yes, the DS1857B-050+ supports up to 128 devices on a single 2-wire bus using its three address pins (A0–A2) and configurable ADEN/ADFIX bits. When ADEN = 0, it responds to two addresses (main and auxiliary); when ADEN = 1, it uses only the main address (default A2h), freeing bus capacity in dense optical module stacks.