Microchip Technology SY69753ALHG-TR

Overview

SY69753ALHG-TR from Micrel Inc. is a 3.3V clock and data recovery (CDR) IC for SONET/SDH OC-3/STS-3 systems, supporting 125Mbps and 155Mbps NRZ data streams with differential PECL I/O, on-chip dual PLL architecture, and link fault detection. It operates across –40°C to +85°C and delivers recovered clock (RCLK/TCLK) and retimed data (RDOUT) outputs with <±200ps skew and 45–55% duty cycle.

For engineers reviewing the SY69753ALHG-TR datasheet, SY69753ALHG-TR pinout, SY69753ALHG-TR application, or SY69753ALHG-TR equivalent, key selection criteria include its 125/155Mbps NRZ CDR capability, dual-PLL clock synthesis and recovery, industrial temperature range, 32-pin EPAD-TQFP package, and compatibility with SONET/SDH/ATM line interface designs requiring low-jitter clock alignment and loss-of-signal resilience.

Technical Context

The SY69753ALHG-TR implements two independent PLLs: one for frequency synthesis using REFCLK as reference (with selectable divide ratios of 8×, 10×, 16×, or 20×), and another for clock recovery synchronized directly to the RDINP/RDINN data stream. The VCO center frequency ranges from 720MHz to 1250MHz, with ±5% tolerance and 15µs acquisition lock time.

It features asynchronous LFIN output indicating PLL lock status (active HIGH when RDIN is within ±1000ppm of synthesizer frequency), carrier detect (CD)-controlled recovery mode switching, and integrated loop filter pins (PLLRN/PLLRP, PLLSP/PLLSN) for external RC tuning. All PECL I/O complies with ECL 100K levels, while TTL inputs/outputs meet standard 3.3V logic thresholds.

Key Specifications

Pinout & Package

SY69753ALHG-TR is housed in a 32-pin EPAD-TQFP (package code H32-1) with exposed thermal pad for enhanced thermal dissipation in high-density line card layouts.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar clock and data recovery applications.

Compared with SY87701AL and ICS87301AGI, the SY69753ALHG-TR uniquely combines dual-PLL architecture, REFCLK holdover, carrier detect control, and SONET-specific lock detection-making it the only option among the three qualified for OC-3 line interface designs requiring guaranteed jitter performance and loss-of-signal resilience.

Availability

SY69753ALHG-TR is available at Aetrix Electronics and suitable for SONET/SDH OC-3 line interfaces, Ethernet media converters, and proprietary 120–180Mbps serial links requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for SY69753ALHG-TR 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

Micrel Inc. was a fabless semiconductor company specializing in high-performance analog, RF, and timing solutions before its acquisition by Microchip Technology in 2015. It pioneered low-power, high-speed CDR and clock management ICs for telecom infrastructure.

The SY69753ALHG-TR belongs to Micrel's SY69xxx family of SONET/SDH-compliant clock recovery ICs, designed specifically for OC-3/STS-3 line interface applications demanding deterministic jitter handling, industrial temperature operation, and integrated fault monitoring.

FAQ

What data rates does the SY69753ALHG-TR support?

The SY69753ALHG-TR supports 125Mbps and 155Mbps NRZ data streams, matching OC-3/STS-3 line rates. Its dual-PLL architecture and VCO range (720–1250MHz) are optimized for these fixed rates-not variable-rate operation. The device achieves full jitter tracking and maintains lock under ±1000ppm frequency deviation, making it unsuitable for broader AnyRate® applications.

How does the SY69753ALHG-TR handle loss of input signal?

When RDIN is lost, the SY69753ALHG-TR uses the REFCLK input to maintain clock output stability. The CD input controls this behavior: with CD HIGH, the receiver PLL attempts lock to RDIN; with CD LOW, the PLL locks exclusively to REFCLK, forcing RDOUT and LFIN LOW. This holdover mode ensures continuous clock output without interruption, critical for SONET hitless protection switching.

What is the purpose of the LFIN output on the SY69753ALHG-TR?

The LFIN output on the SY69753ALHG-TR is an asynchronous TTL signal indicating PLL lock status. It goes HIGH when the receiver PLL is locked to RDIN within ±1000ppm and toggles when unlocked. Unlike a simple lock detect, LFIN remains active during valid data reception and provides real-time diagnostics for system-level fault reporting and automatic failover decisions.

Can the SY69753ALHG-TR generate both recovered and synthesized clocks simultaneously?

Yes-the SY69753ALHG-TR provides separate differential outputs: RCLKP/RCLKN carry the recovered clock, while TCLKP/TCLKN deliver either the recovered clock (when CLKSEL = HIGH) or the synthesized clock (when CLKSEL = LOW). This dual-clock capability enables flexible timing architectures, such as feeding recovered clock to data path and synthesized clock to control logic or parallel interfaces.

What external components are required for stable operation of the SY69753ALHG-TR?

The SY69753ALHG-TR requires two external RC loop filter networks: 680Ω + 1.0µF for the receiver PLL (PLLRN/PLLRP) and 350Ω + 1.0µF for the synthesis PLL (PLLSP/PLLSN). Additionally, proper 3.3V decoupling (0.1µF and 1.0µF ceramics near VCC/VCCA/VCCO pins) and 50Ω termination on all unused PECL outputs are mandatory for jitter performance and signal integrity.