Infineon Technologies CY28409ZXCT

Overview

CY28409ZXCT from Cypress Semiconductor is a programmable clock synthesizer designed for Intel Pentium 4–class CPU platforms, delivering three differential 100/133/200/266/400 MHz CPU clock pairs, one differential 100/200 MHz SRC clock, ten 33 MHz PCI clocks, five 66 MHz 3V66 clocks (one selectable as 48 MHz), and two fixed 48 MHz USB clocks-all from a single 14.318 MHz crystal reference. It supports I²C-based configuration, spread-spectrum EMI reduction, and power-down control via dedicated STP# inputs.

For engineers reviewing the CY28409ZXCT datasheet, CY28409ZXCT pinout, CY28409ZXCT application, or CY28409ZXCT equivalent, key selection criteria include differential CPU/SRC clock integrity, SMBus-configurable output enables and drive modes, FS_A/FS_B frequency select logic timing relative to VTT_PWRGD#, and 56-pin SSOP/TSSOP thermal and routing constraints in high-density motherboard layouts.

Technical Context

The CY28409ZXCT integrates two PLLs: PLL1 locks to the 14.318 MHz crystal (XIN/XOUT) to generate a stable 100/200 MHz SRC base, while PLL2 derives CPU frequencies (100–400 MHz) and 66 MHz 3V66 outputs with configurable division and spread-spectrum modulation. All outputs are independently enabled/disabled and configured for drive strength and stop behavior via eight SMBus-accessible control registers.

Frequency selection is determined by FS_A/FS_B logic levels sampled synchronously on VTT_PWRGD# assertion, enabling boot-time CPU clock configuration without firmware intervention. The serial interface supports byte/block read/write operations at slave address 0xD2, with register bit fields controlling output enable, three-state behavior during STP#, and VCH mode selection for the 3V66_4 pin.

Key Specifications

Pinout & Package

56-pin SSOP and TSSOP package with 0.5 mm pitch; thermally optimized for motherboard clock distribution near CPU socket and chipset. Power and ground pins are distributed across multiple domains to minimize noise coupling between CPU, SRC, PCI, and USB clock sections.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ICS952006AGT, CY28409ZXCT adds SMBus readback, VCH mode, and Lexmark spread spectrum-critical for EMI-critical desktop platforms. Versus ICS952017AGT, it retains external crystal control for tighter ppm tolerance and field-replaceable timing sources.

Availability

CY28409ZXCT is available at Aetrix Electronics and suitable for desktop motherboard design, Intel Pentium 4 reference platform validation, and legacy PCI expansion systems requiring stable component supply and long-term lifecycle support.

Supply support for CY28409ZXCT 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 fabless semiconductor company specializing in timing, memory, and programmable logic solutions for computing and communications infrastructure.

The CY28xxx clock synthesizer product line targets high-performance x86 platform timing, emphasizing differential clock integrity, multi-domain power isolation, and Intel-compliant frequency agility for Pentium 4 and early Core architectures.

FAQ

What crystal specifications are mandatory for CY28409ZXCT operation?

The CY28409ZXCT requires a 14.31818 MHz parallel-resonant AT-cut crystal with 20 pF load capacitance, maximum 0.1 mW drive level, and ≤50 ppm initial tolerance. Substituting a series-resonant crystal causes ≥300 ppm frequency error and violates Intel timing specifications.

How does VTT_PWRGD# affect CPU clock initialization?

VTT_PWRGD# is a level-sensitive input that latches FS_A/FS_B states when driven LOW, signaling stable CPU VTT voltage. Once sampled, further transitions on FS_A, FS_B, or VTT_PWRGD# are ignored-ensuring deterministic CPU clock selection before processor reset release.

Can all clock outputs be disabled independently via SMBus?

Yes-Registers 1–5 provide individual enable/disable bits for all 22 outputs: CPUT0–CPUT2, CPUC0–CPUC2, SRCT/SRCC, PCI0–PCI6, PCIF0–PCIF2, USB_48, DOT_48, 3V66_0–3V66_4/VCH, and REF_0/REF_1. Each bit controls output buffer activation and three-state behavior.

What is the functional difference between PCIF and PCI outputs?

PCIF0–PCIF2 are free-running 33 MHz clocks derived directly from the 3V66 source and remain active during PCI_STP# assertion unless explicitly disabled. PCI0–PCI6 are synchronous 33 MHz clocks gated by PCI_STP# and stop immediately upon assertion-meeting Intel's PCI bus power management requirements.