Analog Devices Inc./Maxim Integrated DS21Q55

Overview

DS21Q55 from Maxim Integrated is a quad-channel, software-selectable T1/E1/J1 transceiver IC with integrated line interface units (LIUs), framers, dual HDLC controllers, and TDM backplane interface. It supports long-haul and short-haul operation, delivers programmable termination (75Ω/100Ω/120Ω), provides crystal-less jitter attenuation, and synthesizes 16.384MHz/8.192MHz/4.096MHz/2.048MHz clocks locked to recovered network timing - deployed in CSUs, DSUs, and channel banks.

For engineers reviewing the DS21Q55 datasheet, DS21Q55 pinout, DS21Q55 application, or DS21Q55 equivalent, key selection considerations include per-port T1/E1/J1 mode configurability, dual HDLC controller support, elastic-store slip buffer operation up to 16.384MHz, CMI coding capability for optical interfaces, and Intel/Motorola bus compatibility via 8-bit parallel port.

Technical Context

The DS21Q55 implements four independent transceiver channels, each integrating a full LIU (transmit waveshaping + receive clock/data recovery), framer, and dual HDLC controllers. Transmit waveform generation includes DSX-1 and CSU line build-outs (–7.5dB, –15dB, –22.5dB) for T1 and G.703-compliant 75Ω coax / 120Ω twisted-pair outputs for E1.

Each channel features dual two-frame elastic-store slip buffers for asynchronous backplane interfacing, programmable BERT generator/detector, and software-selectable receive/transmit termination resistors. The device uses an extended system information bus (ESIB) for multi-device synchronization and supports JTAG boundary scan per IEEE 1149.1.

Key Specifications

Pinout & Package

DS21Q55 is housed in a 256-ball BGA package measuring 27mm × 27mm with 1.27mm ball pitch. Pin functions are organized into five functional groups: line interface pins (T1/E1 differential pairs), parallel control port (8-bit Intel/Motorola bus), extended system information bus (ESIB), JTAG test access port, and power/ground distribution.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad T1/E1 transceiver applications.

Compared with DS21Q55, DS21Q55N offers identical electrical and functional behavior with extended temperature qualification, while DS21Q35 reduces port count and feature depth - neither is pin-compatible nor functionally interchangeable without firmware and layout revision.

Availability

DS21Q55 is available at Aetrix Electronics and suitable for channel service units, data service units, and T1/E1 test equipment requiring stable component supply, long-term lifecycle assurance, and traceable sourcing from authorized channels.

Supply support for DS21Q55 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 high-performance analog, mixed-signal, and RF solutions for communications, computing, and industrial markets.

The DS21Q55 belongs to Maxim's telecom line interface product line, designed specifically for multi-port T1/E1/J1 infrastructure equipment requiring integrated framing, HDLC, jitter control, and flexible media interface support.

FAQ

What is the operating temperature range for the DS21Q55?

The DS21Q55 is specified for commercial operation from 0°C to +70°C ambient temperature. This range aligns with standard indoor telecom equipment environments such as central office racks and enterprise router chassis. For extended temperature applications, the DS21Q55N variant supports –40°C to +85°C and shares identical functionality and pinout with the DS21Q55.

Does the DS21Q55 support both T1 and E1 framing simultaneously across its four ports?

Yes, the DS21Q55 supports independent software-selectable T1, E1, or J1 operation on each of its four ports. Each port's framer, LIU, and HDLC controllers are fully configurable via internal registers, enabling mixed-mode operation - for example, Port 1 as T1, Port 2 as E1, Port 3 as J1, and Port 4 as E1 - without hardware change.

What clock synthesis capabilities does the DS21Q55 provide?

The DS21Q55 integrates a programmable backplane clock synthesizer that generates 16.384MHz, 8.192MHz, 4.096MHz, or 2.048MHz outputs, all phase-locked to the recovered network clock. This eliminates the need for separate clock generators and ensures deterministic timing alignment between the TDM backplane and line interface domains.

How does the DS21Q55 handle jitter in long-haul T1/E1 applications?

The DS21Q55 incorporates a crystal-less jitter attenuator per channel that meets ITU-T G.823 and GR-499-CORE requirements for long-haul operation. It filters input jitter up to 1.5UI peak-to-peak and provides clean, low-jitter clock recovery without external VCXO components - reducing bill-of-materials and improving thermal stability.

Is the DS21Q55 pin-compatible with other devices in the DS21Qx5y family?

Yes, the DS21Q55 is explicitly documented as pin compatible with the DS21Qx5y family of products, including DS21Q35 and DS21Q45. This allows scalable port-count designs using shared PCB layouts and firmware abstraction layers, provided software accounts for per-device register map differences and feature subsets.