Skyworks Solutions Inc. CY2SSTV855ZXC

Overview

CY2SSTV855ZXC from Silicon Labs is a differential zero-delay clock buffer IC designed for DDR SDRAM timing distribution. It delivers 1:5 SSTL_2 differential outputs with <100 ps output skew, ±450 ps static phase offset, and supports 60–170 MHz input frequencies in industrial-grade operation (–40°C to +85°C). It serves as a PLL-based clock synchronizer in memory subsystems of servers and networking equipment.

For engineers reviewing the CY2SSTV855ZXC datasheet, CY2SSTV855ZXC pinout, CY2SSTV855ZXC application, or CY2SSTV855ZXC equivalent, key selection criteria include its Spread Aware™ EMI reduction capability, external feedback loop configuration (FBINT/FBINC), power-down control (PWRDWN), and 28-pin TSSOP package compatibility with JEDEC DDR timing requirements.

Technical Context

The CY2SSTV855ZXC implements a PLL-based zero-delay architecture where the external feedback path (FBOUTT/FBOUTC → FBINT/FBINC) eliminates propagation delay by aligning output edges with the CLKINT/CLKINC reference. Its PLL remains active only above 20 MHz input frequency; below that threshold, it disables outputs and shuts down the PLL.

It operates with dual 2.5 V supplies: VDDQ powers SSTL_2 output buffers, while AVDD supplies the PLL core. When AVDD is grounded, the PLL bypasses and routes the input clock directly to outputs-enabling test-mode functionality without PLL involvement.

Key Specifications

Pinout & Package

Package: 28-pin TSSOP (JEDEC MO-153, 4.4 mm body width, lead-free ZXC suffix), 0.65 mm pitch, 9.8 mm × 4.4 mm footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar differential clock buffer applications.

Compared with IDT 8T49N241 and ON Semi NB3N551, the CY2SSTV855ZXC uniquely combines zero-delay PLL operation, Spread Aware™ SSC tracking, and industrial-grade SSTL_2 drive in a minimal 28-pin TSSOP - making it optimal for DDR2 memory timing where deterministic phase alignment and EMI control are critical.

Availability

CY2SSTV855ZXC is available at Aetrix Electronics and suitable for DDR2 memory subsystems, server memory modules, and industrial embedded controllers requiring stable component supply, long-term lifecycle support, and lead-free compliance.

Supply support for CY2SSTV855ZXC 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

Silicon Labs is a fabless semiconductor company specializing in timing, wireless, and MCU solutions, with deep expertise in precision clock generation and low-jitter signal integrity.

The CY2SSTV855ZXC belongs to Silicon Labs' legacy timing portfolio targeting DDR memory interface applications; it was engineered specifically to meet JEDEC-compliant zero-delay clock distribution requirements in high-speed memory systems.

FAQ

What is the primary function of the CY2SSTV855ZXC in a DDR memory system?

The CY2SSTV855ZXC functions as a zero-delay differential clock buffer that distributes a single SSTL_2 reference clock to four DDR memory channels plus a feedback path. Its PLL-based architecture aligns output edges with the input reference using external feedback (FBINT/FBINC), achieving sub-100 ps skew and deterministic phase offset - essential for meeting DDR2 tAC and tDS timing budgets.

Does the CY2SSTV855ZXC support spread spectrum clocking (SSC)?

Yes, the CY2SSTV855ZXC is Spread Aware™ and supports tracking of spread spectrum clock inputs with modulation frequencies from 30 kHz to 33.3 kHz and downspread up to –0.5%. This capability reduces electromagnetic interference without causing PLL unlock, unlike non-Spread Aware buffers that may lose lock or introduce jitter under SSC conditions.

How does the PWRDWN pin affect the operation of the CY2SSTV855ZXC?

When PWRDWN is driven HIGH, the CY2SSTV855ZXC disables all differential outputs (YT/YC/FBOUT) into high-impedance state and shuts down the PLL, drawing minimal current. When LOW, normal operation resumes with PLL lock and output enable. The transition times are specified as tPLZ < 10 ns and tPZH < 30 ns, enabling fast clock gating in power-aware DDR controllers.

What is the role of the AVDD pin on the CY2SSTV855ZXC, and what happens if it is grounded?

The AVDD pin supplies 2.5 V to the internal PLL circuitry. If AVDD is tied to GND, the PLL is disabled and bypassed, routing the CLKINT/CLKINC input directly to the YT/YC outputs - a test mode that eliminates PLL-related jitter and lock time. This mode is explicitly supported in the datasheet for board validation and debug.

Can the CY2SSTV855ZXC operate with input frequencies below 60 MHz?

Yes - the CY2SSTV855ZXC supports input frequencies as low as DC for bypass mode (AVDD = GND), and automatically enters low-frequency power-down mode when CLKINT/CLKINC falls below 20 MHz: outputs go Hi-Z and the PLL shuts off. However, AC specifications (jitter, skew, phase offset) are only guaranteed for 60–170 MHz operation per the datasheet's AC Electrical Specifications table.