Analog Devices Inc./Maxim Integrated DS21554LB+

Overview

DS21554LB+ from Maxim Integrated is a 5V single-chip E1 transceiver IC designed for CEPT PCM-30/ISDN-PRI line interface applications. It integrates clock/data recovery, G.703 waveshaping for 75Ω coax and 120Ω twisted-pair, 32-bit or 128-bit crystal-less jitter attenuation, HDLC controller with 64-byte buffers, and full ITU-T G.703/G.704/G.706/G.823 compliance. Used in telecom access equipment for E1 line termination.

For engineers reviewing the DS21554LB+ datasheet, DS21554LB+ pinout, DS21554LB+ application, or DS21554LB+ equivalent, key selection criteria include E1 framer support for FAS/CAS/CCS/CRC4 formats, dual elastic store slip buffers for asynchronous backplane interfacing up to 8.192MHz, IEEE 1149.1 JTAG boundary scan, and programmable output clocks for fractional E1/H0/H12 systems.

Technical Context

The DS21554LB+ implements a fully independent transmit and receive path architecture with separate elastic stores, enabling phase/frequency alignment between recovered E1 data (2.048MHz) and asynchronous backplane clocks (1.544/2.048/4.096/8.192MHz). Its framer performs frame/multiframe synchronization, CAS signaling extraction/insertion, and alarm detection (RLOS, AIS, RRA, RAIS).

Jitter attenuation is selectable between 32-bit and 128-bit depths and configurable in either transmit or receive data path. The on-chip HDLC controller supports Sa-bit links or DS0/sub-DS0 operation with hardware-based signaling reinsertion and signaling freeze interrupt generation on data change.

Key Specifications

Pinout & Package

DS21554LB+ is housed in a 100-pin LQFP package (14mm × 14mm), RoHS-compliant and lead-free. Pin assignments are validated per Maxim's official DS21554 datasheet Rev 021004, with dedicated signal groups for line interface (RRING/RTIP/TRING/TTIP), parallel control port (D0–D7, A0–A7, RD/WR, CS), elastic store clocks (RSYSCLK/TSYSCLK), and JTAG test access (TCK/TMS/TDI/TDO).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar E1 transceiver applications.

Compared with DS21554LN+, the DS21554LB+ trades extended temperature capability for lower cost in commercial indoor applications; compared with DS2154L+, it delivers measurable design value through integrated HDLC, JTAG testability, and flexible clock synthesis - reducing external component count by ≥7 parts per channel.

Availability

DS21554LB+ is available at Aetrix Electronics and suitable for DSLAM line cards, E1 multiplexers, remote terminal units, and ISDN-PRI gateways requiring stable component supply across multi-year telecom deployments.

Supply support for DS21554LB+ 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 U.S.-based semiconductor company specializing in high-performance analog, mixed-signal, and RF solutions for communications, industrial, and computing markets.

The DS21554LB+ belongs to Maxim's Single-Chip Transceiver (SCT) product line, engineered specifically for carrier-grade E1 line interface applications demanding full G.703/G.704 compliance, low-jitter clock recovery, and robust alarm handling in telecom infrastructure.

FAQ

What is the operating temperature range for the DS21554LB+?

The DS21554LB+ is rated for commercial temperature operation from 0°C to +70°C. This range aligns with standard indoor telecom equipment environments such as central office racks and enterprise PBX systems. For extended temperature applications like outdoor cabinets or base stations, the DS21554LN+ variant (–40°C to +85°C) is recommended. Both share identical electrical characteristics and pinout, enabling drop-in replacement where thermal margins allow.

Does the DS21554LB+ support both 75Ω coaxial and 120Ω twisted-pair E1 interfaces?

Yes, the DS21554LB+ supports both 75Ω coaxial and 120Ω twisted-pair E1 interfaces per ITU-T G.703. Its line interface circuitry includes programmable line build-out (LBO) control via the LICR register, allowing configuration for short-haul (0–270m) or long-haul (up to 2km) twisted-pair operation, as well as 75Ω coax drive with proper transformer coupling. Reference schematics in the official datasheet confirm dual-interface validation.

How does the jitter attenuation function work in the DS21554LB+?

The DS21554LB+ incorporates a crystal-less jitter attenuator configurable for either 32-bit or 128-bit depth and assignable to either the transmit or receive data path. It uses an internal VCO/PLL architecture to filter input jitter without requiring an external crystal, meeting G.823 recommendations for wander and jitter transfer. The attenuation depth directly impacts latency: 32-bit introduces ~16µs delay, while 128-bit adds ~64µs - a key trade-off for real-time voice or sync-sensitive applications.

Can the DS21554LB+ operate with asynchronous backplane clocks?

Yes, the DS21554LB+ supports asynchronous backplane interfacing via dual independent elastic store slip buffers - one on the receive side (RSYSCLK) and one on the transmit side (TSYSCLK). Each accepts clock inputs of 1.544MHz, 2.048MHz, 4.096MHz, or 8.192MHz, enabling seamless integration with non-synchronized system buses. This eliminates the need for external FIFOs or clock-domain-crossing logic in multi-processor telecom architectures.

Is the DS21554LB+ pin-compatible with earlier Maxim E1 transceivers?

Yes, the DS21554LB+ is explicitly pin-compatible with the DS2154/DS2152/DS21352/DS21552 family of SCTs, as confirmed in the "Features" section of the datasheet. This allows direct PCB replacement in legacy designs without layout changes. However, firmware updates may be required to leverage new capabilities like the HDLC controller, JTAG boundary scan, or interleaved PCM bus operation - all of which are disabled by default for backward compatibility.