Cypress Semiconductor Corp CY7B951-SXI

Overview

CY7B951-SXI from Cypress Semiconductor is a SONET/SDH and ATM-compatible local area network transceiver IC that recovers clock and data from 51.84-MHz or 155.52-MHz NRZ/NRZI serial streams, provides differential transmit buffering (TOUT±), and delivers ECL 100K-compatible recovered outputs (RCLK±, RSER±, ROUT±). It operates on a single +5V supply in 24-pin SOIC and supports fiber, coaxial, and twisted-pair media.

For engineers reviewing the CY7B951-SXI datasheet, CY7B951-SXI pinout, CY7B951-SXI application, or CY7B951-SXI equivalent, key selection criteria include its dual-rate PLL architecture (51.84/155.52 MHz), ±1% frequency agility, carrier detect–controlled lock behavior, loopback test capability, and integrated power-down modes for RCLK±/RSER±, TCLK±, and output buffers.

Technical Context

The CY7B951-SXI integrates two independent PLLs: a Receive CDR PLL that locks to RIN± using REFCLK×8 as center frequency reference, and a Transmit frequency multiplier PLL that synthesizes TCLK± at exactly 8×REFCLK. Both PLLs are mode-selected via the 3-level MODE pin (VCC/GND/floating) to support STS-1 (51.84 MHz) or STS-3 (155.52 MHz) line rates.

Its receiver includes a transition detector (512-bit-time timeout), Out-of-Lock detection, and Carrier Detect (CD)-gated LFI logic that forces PLL alignment to REFCLK×8 when CD is low. The LOOP pin enables internal TSER±→Receive-PLL routing for full-path functional testing excluding RIN± and TOUT± drivers.

Key Specifications

Pinout & Package

Package: 24-pin SOIC (Small Outline Integrated Circuit), surface-mount, Pb-free option available.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ATM/SONET transceiver applications.

Compared with PM5345-SUNI and ICS873001AGI, the CY7B951-SXI uniquely combines dual-rate operation, integrated LFI/CD logic, hardware loopback, and per-output power-down in a 24-pin SOIC-reducing BOM count and enabling field-reconfigurable line cards.

Availability

CY7B951-SXI is available at Aetrix Electronics and suitable for SONET/SDH line cards, ATM edge switches, factory test systems, and multi-rate protocol analyzers requiring stable component supply and long-term lifecycle support.

Supply support for CY7B951-SXI 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

Cypress Semiconductor (now part of Infineon Technologies) designs high-performance mixed-signal ICs for communications, computing, and industrial applications, with emphasis on integration and system-level reliability.

The CY7B951 belongs to Cypress's legacy LAN transceiver product line, engineered specifically for SONET/SDH and ATM physical layer interfacing-prioritizing jitter tolerance, media flexibility, and testability in telecom infrastructure.

FAQ

What is the function of the MODE pin, and how does it affect REFCLK requirements?

The MODE pin is a 3-level input that selects operating frequency: VCC enables 155.52-MHz mode requiring 19.44-MHz ±1% REFCLK; GND enables 51.84-MHz mode requiring 6.48-MHz ±1% REFCLK; floating enables test mode. REFCLK×8 must match the target bit rate within 1000 ppm for reliable lock.

How does the Carrier Detect (CD) pin influence LFI and PLL behavior?

When CD is at ECL HIGH, the Receive PLL tracks RIN± normally and LFI reflects transition and lock status. When CD is at ECL LOW, the PLL locks to REFCLK×8, RSER± holds LOW, and LFI goes LOW-indicating forced alignment. At TTL LOW, only OOL affects LFI.

Can the CY7B951-SXI drive optical modules directly, or is additional circuitry required?

The CY7B951-SXI does not drive lasers or photodiodes directly. Its TOUT± outputs are ECL 100K-compatible and intended for PCB traces, coaxial cable, or twisted pair. Driving optical modules requires external laser driver or limiting amplifier ICs matched to the module's electrical interface.

What happens to the Receive PLL when both RCLK± and RSER± outputs are left unconnected?

Leaving both RCLK± and RSER± unconnected (or tying them to VCC) disables the entire Receive PLL, halting clock/data recovery and reducing current draw. The device retains power to other blocks (e.g., TCLK± generation, LFI logic), but RIN± is ignored until outputs are re-enabled.