CY2281

The CY2281 is a clock synthesizer/driver for Pentium II, or other similar processor-based mobile PCs requiring up to 100 MHz support. The CY2281 outputs two CPU clocks at 2.5V.

There are six PCI clocks, running at one-half or one-third the CPU clock frequency of 66.6 MHz and 100 MHz respectively.

One of the PCI clocks is free-running. Additionally, the part outputs one 3.3V reference clock at 14.318 MHz. The CY2281-2S also provides one 3.3V USB clock at 48 MHz.

The CY2281-11S and CY2281-2S incorporate the Intel®-defined spread spectrum feature. They provide a 0.6% downspread on the CPU and PCI clocks, which can help reduce EMI in certain high-speed systems. A summary of clock outputs for both devices is shown below.

The part possesses power-down, CPU stop, and PCI stop pins for power management control. The signals are synchronized on-chip, and ensure glitch-free transitions on the outputs.

When the CPU_STOP input is asserted, the CPU clock outputs are driven LOW. When the PCI_STOP input is asserted, the PCI clock outputs (except the free-running PCI clock) are driven LOW. When the PWR_DWN pin is asserted, the reference oscillator and PLLs are shut down, and all outputs are driven LOW.

The CY2281 clock outputs are designed for low EMI emissions.

Controlled rise and fall times, unique output driver circuits, and innovative circuit layout techniques enable the CY2281 to have lower EMI than clock devices from other manufacturers.

Additionally, factory-EPROM programmable output drive and slew-rate control enable optimal configurations.