SM561

The Cypress SM561 is a Spread Spectrum Clock Generator (SSCG) IC used for the purpose of reducing EMI found in today's high-speed digital electronic systems.

The SM561 uses a Cypress proprietary phase-locked loop (PLL) and Spread Spectrum Clock (SSC) technology to synthesize and frequency modulate the input frequency of the reference clock. By frequency modulating the clock, the measured EMI at the fundamental and harmonic frequencies of Clock (SSCLK) is greatly reduced.

This reduction in radiated energy can significantly reduce the cost of complying with regulatory requirements and time to market without degrading the system performance.

The SM561 is a very simple and versatile device to use. The frequency and spread% range is selected by programming S0 and S1 digital inputs. These inputs use three (3) logic states including High (H), Low (L), and Middle (M) to select one of the nine available Frequency Modulation and Spread% ranges. Refer to Table for programming details.

The SM561 is intended for use with applications with a reference frequency in the range of 54 to 166 MHz. A wide range of digitally selectable spread percentages is made possible by using Tri-level (High, Low, and Middle) logic at the S0 and S1 digital control inputs. The output spread (frequency modulation) is symmetrically centered on the input frequency.

Spread Spectrum Clock Control (SSCC) function enables or disables the frequency spread and is provided for easy comparison of system performance during EMI testing.

The SM561 is available in an eight-pin SOIC package with a 0°C-to-70°C operating temperature range. Refer to the SM560 data sheet for operation at frequencies from 25 to 108 MHz.