CY28RS400ZXCT

Application Specific Clock/Timing Overview

The CY28RS400ZXCT is a processor-specific clock generator designed for the ATI RS400 chipset and Intel CPU platforms. It features two internal PLL circuits capable of generating frequencies up to 266MHz. The device accepts LVTTL or crystal inputs and provides differential CPU clock pairs, 100MHz differential SRC clocks, a 48MHz USB clock, and a 33MHz PCI clock. It operates on a 3.3V supply (3.135V to 3.465V) within an ambient temperature range of 0°C to 70°C. The component is housed in a 56-pin TFSOP package.

Application Specific Clock/Timing Feature Summary

• Supports selectable CPU frequencies via hardware straps (FS_A, FS_B, FS_C) with I2C readback capabilities.
• Generates differential CPU clock pairs, 100MHz differential serial reference clocks, 48MHz USB, and 33MHz PCI outputs.
• Includes Lexmark spread spectrum profile support for electromagnetic interference reduction.
• Features SMBus-compatible serial interface for individual output buffer enable/disable control.

Application Specific Clock/Timing Applications

• ATI RS400 Chipset systems
• Intel CPU motherboards
• Minicard specifications

Application Specific Clock/Timing Procurement Notes

Verify the manufacturer origin as Infineon Technologies acquired Cypress Semiconductor assets. Confirm the 56-TSSOP II package type matches the design footprint. Ensure the 3.3V power supply tolerance aligns with system rails. Check RoHS3 compliance status for environmental regulations. Note that this specific part number may be discontinued; verify current availability through authorized distributors.

Application Specific Clock/Timing Selection Notes

Select this component when designing for ATI RS400 or compatible Intel CPU architectures requiring specific frequency tables. Ensure the application utilizes a parallel resonance crystal at 14.318MHz for accurate timing. Verify that the PCB layout accommodates the 56-pin TFSOP package dimensions. Confirm that the system supports the required 3.3V logic levels for input signals like VTT_PWRGD# and CLKREQ#.

Application Specific Clock/Timing Part Context

The CY28RS400 series was originally developed by Cypress Semiconductor Corporation for specific chipset requirements. Following corporate acquisitions, manufacturing and distribution rights transitioned to Infineon Technologies. This component represents a specialized solution for legacy desktop and server platforms utilizing the RS400 northbridge architecture.

Application Specific Clock/Timing Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. Users should consult official replacement guides from Infineon Technologies for end-of-life management strategies.

Application Specific Clock/Timing FAQ

How is the CPU frequency selected?

CPU frequency selection is achieved by applying logic levels to the FS_A, FS_B, and FS_C pins prior to asserting VTT_PWRGD#. The device samples these values once the processor VTT voltage is stable.

What type of crystal is required?

The CY28RS400 requires a parallel resonance crystal operating at 14.318MHz. Using a series resonance crystal will cause frequency errors and violate ppm specifications.

How does the power-down function work?

The VTT_PWRGD#/PD pin serves a dual function. After initial power-up sampling, it acts as an asynchronous active-high input to shut off all clocks cleanly before power removal.