Cypress Semiconductor Corp CY7B951-SXC

Overview

CY7B951-SXC 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 packaging and supports fiber, coaxial, and twisted-pair media interfaces.

For engineers reviewing the CY7B951-SXC datasheet, CY7B951-SXC pinout, CY7B951-SXC application, or CY7B951-SXC equivalent, key selection considerations 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 TOUT±, ROUT±, RCLK±, RSER±, and TCLK±.

Technical Context

The CY7B951-SXC integrates two independent PLLs: a Receive CDR PLL that locks to incoming RIN± data using REFCLK×8 as center-frequency reference, and a Transmit frequency multiplier PLL that synthesizes TCLK± at exactly 8×REFCLK. Both PLLs support selectable 51.84 MHz (MODE = GND) or 155.52 MHz (MODE = VCC) operation with ±1% frequency tolerance.

Its receiver includes a transition detector (512-bit-time timeout), Out-of-Lock detection, and Carrier Detect (CD)-gated LFI output with TTL-level status signaling. The LOOP pin enables internal TSER±-to-RX-PLL loopback for system-level validation without external media, while all ECL outputs support power-down via VCC tie-off or floating.

Key Specifications

Pinout & Package

Package: 24-pin Small Outline Integrated Circuit (SOIC), surface-mount, 300-mil body width.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PM5345-SUNI and ICS871001AGI, the CY7B951-SXC uniquely combines dual-rate operation, integrated carrier detect handling, hardware loopback, and ECL 100K drive strength-all in a single +5V SOIC package-making it optimal for field-deployable ATM edge devices requiring robust link supervision and media flexibility.

Availability

CY7B951-SXC is available at Aetrix Electronics and suitable for SONET STS-1/STS-3 line interfaces, ATM cell processor interconnects, and factory test systems requiring stable component supply and long-term obsolescence management.

Supply support for CY7B951-SXC 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) is a U.S.-based semiconductor company specializing in programmable system-on-chip (PSoC), memory, and high-performance interface solutions for communications and industrial markets.

The CY7B951 belongs to Cypress's legacy communications transceiver product line, engineered specifically for SONET/SDH and ATM physical layer implementations where deterministic clock recovery, media-agnostic I/O, and built-in diagnostics were critical design requirements.

FAQ

What reference clock frequencies are required for 51.84-MHz and 155.52-MHz operation?

The CY7B951-SXC requires a 6.48 MHz ±1% reference clock for 51.84-MHz operation (MODE = GND) and a 19.44 MHz ±1% reference clock for 155.52-MHz operation (MODE = VCC). REFCLK is multiplied internally by eight in both cases. The REFCLK± input accepts either differential PECL or single-ended TTL signals, with automatic mode detection based on input voltage levels.

How does the Carrier Detect (CD) pin affect Link Fault Indicator (LFI) behavior?

When CD is driven HIGH (ECL level), LFI reflects combined status of transition detection and PLL lock. When CD is pulled LOW (ECL level), LFI goes LOW and the RX-PLL locks to REFCLK×8 regardless of RIN± activity. When CD is at TTL LOW (<0.8 V), transition detection is disabled and LFI indicates only Out-of-Lock condition-enabling selective fault isolation in optical or copper systems.

Can the CY7B951-SXC operate without an external reference clock?

No. The CY7B951-SXC requires an external REFCLK input to function: the Receive CDR PLL uses REFCLK×8 as its center frequency reference, and the Transmit PLL uses the same multiplied signal to generate TCLK±. There is no internal oscillator or crystal driver. Leaving REFCLK unconnected disables both PLLs and prevents clock/data recovery or transmit clock generation.

What happens to power consumption when ECL outputs are disabled?

Disabling any ECL output pair (e.g., tying RCLK± to VCC or leaving it floating) reduces current draw by ~4 mA per pair. Disabling both RCLK± and RSER± powers down the entire Receive PLL; disabling TCLK± powers down the Transmit PLL. Total quiescent current drops below 65 mA proportionally-critical for thermal management in dense line-card deployments.