Analog Devices Inc./Maxim Integrated DS2187S

Overview

DS2187S from Maxim Integrated (now part of Analog Devices) is a T1/CEPT receive line interface IC for primary-rate digital telecommunication networks. It extracts clock and data from twisted-pair or coaxial lines, supports AMI/B8ZS/HDB3 decoding, features on-chip PLL with laser-trimmed VCO, and operates from a single 5V supply in 20-pin SOIC.

For engineers reviewing the DS2187S datasheet, DS2187S pinout, DS2187S application, or DS2187S equivalent, key selection considerations include T1/CEPT mode selection via RCLKSEL, LOCK status monitoring, bipolar violation (BPV) reporting, and compliance with TR 62411, PUB 43801, and G.823 jitter and alarm specifications.

Technical Context

The DS2187S implements dual-loop clock recovery: a high-Q frequency-locked loop (FLL) for stable average-frequency tracking and a digital phase-locked loop (DPLL) for precise jitter attenuation. In T1 mode (RCLKSEL = 0), it uses an 18.528 MHz reference divided by 11–13; in CEPT mode (RCLKSEL = 1), it uses 24.576 MHz similarly divided.

It processes differential line inputs (RTIP/RRING) with internal peak detection and adaptive slicing, supports zero-code suppression (ZCSEN), and reports real-time alarms including AIS, RCL, and BPV - all synchronized to the recovered RCLK output with ≤75 ns propagation delay.

Key Specifications

Pinout & Package

DS2187S is packaged in a 20-pin SOIC (300-mil width), with separate analog (AVDD/AVSS) and digital (DVDD/DVSS) power domains to minimize noise coupling between high-speed data recovery and precision analog circuitry.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar receive line interface applications.

Compared with DS2187N and DS2155, the DS2187S offers optimal trade-off for dedicated receive-only applications: superior SOIC thermal dissipation, full alarm reporting granularity, and explicit T1/CEPT mode control - making it ideal for CSU, DACS, and PABX interface designs requiring compliance-grade jitter and alarm behavior.

Availability

DS2187S is available at Aetrix Electronics and suitable for channel banks, DACS terminals, PABX-to-computer interfaces (DMI/CPI), and CSU/DSU line termination requiring stable component supply and long-lifecycle support.

Supply support for DS2187S 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 (acquired by Analog Devices in 2021) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management solutions for communications, industrial, and computing markets.

The DS2187S belongs to Maxim's telecom line interface product line, designed specifically for short-loop T1/CEPT terminal equipment such as CSUs, DACS, and PABX gateways requiring standards-compliant clock recovery and alarm reporting.

FAQ

What is the function of the RCLKSEL pin on the DS2187S?

The RCLKSEL pin on the DS2187S selects between T1 (1.544 MHz) and CEPT (2.048 MHz) operating modes: tying it to AVSS configures the device for T1 with an 18.528 MHz internal reference, while tying it to DVDD selects CEPT mode using 24.576 MHz. This pin directly determines the DPLL divide ratio and FLL reference, and incorrect configuration will prevent proper clock lock. The DS2187S must be configured at power-up and cannot switch modes dynamically during operation.

How does the DS2187S handle B8ZS and HDB3 line coding?

The DS2187S decodes both B8ZS (in T1 mode) and HDB3 (in CEPT mode) automatically. When ZCSEN is high, it replaces decoded B8ZS or HDB3 code words with all-0 sequences at RPOS and RNEG outputs; when ZCSEN is low, original coded data passes through unchanged. BPV output remains active for violations except when ZCSEN=1 and RCLKSEL=1 (CEPT mode), where BPV is disabled per specification. This behavior is confirmed in the DS2187S datasheet Pin Description Table 1 and Zero-Code Suppression section.

What does the LOCK pin indicate on the DS2187S?

The LOCK pin on the DS2187S goes high only when both the FLL has achieved frequency lock *and* the DPLL has achieved phase lock to the incoming line signal - confirming valid, jitter-compliant RCLK and RPOS/RNEG outputs. It transitions low during carrier loss (RCL high), loss of signal, or excessive input jitter. The DS2187S requires ≥50 ms after signal reacquisition to assert LOCK high, as specified in the Analog Electrical Characteristics table. LOCK is not asserted during initial power-up until synchronization completes.

Can the DS2187S operate with a single shared 5V supply for both analog and digital sections?

Yes, the DS2187S can operate with a single 5V supply connected to both AVDD and DVDD, and AVSS and DVSS tied together, provided the supply is well-decoupled with ≥10 µF bulk and 0.1 µF ceramic capacitors near each supply pin. The DS2187S datasheet explicitly states that tying analog and digital supplies together "will not degrade its performance" under proper decoupling. However, for optimal jitter performance in sensitive applications like CSU line cards, separate analog/digital rails are recommended to isolate high-speed digital switching noise from the analog front-end.

What is the purpose of the LCAP pin on the DS2187S?

The LCAP pin on the DS2187S connects to the internal FLL loop filter and requires an external 10 µF capacitor to AVSS (not DVSS) to stabilize loop dynamics and ensure compliant jitter transfer per TR 62411. This capacitor sets the dominant pole of the FLL control loop; omitting it or using incorrect value causes unstable lock, excessive output jitter, or failure to acquire lock. The DS2187S datasheet specifies "attach a 10 microfarad capacitor from this pin to VSS" - and VSS here refers to AVSS, as confirmed in the Bypassing and Layout Considerations section.