CYIFS731 Datasheet, PDF (1/20 Pages) Cypress Semiconductor – Reduces Systemic EMI

CYIFS731
Low EMI Spread Spectrum Clock
Low EMI Spectrum Spread Clock
Features
■ Reduces Systemic EMI.
■ Modulates external clocks including crystals, crystal oscillators
and ceramic resonators.
■ 1X and 2X modulated frequency outputs.
■ Modulation programmable with simple external loop filter (LF).
■ 4 to 68 MHz operating frequency range.
■ Digitally controlled modulation.
■ TTL/CMOS compatible outputs.
■ Center Spread Modulation.
■ Low short term jitter.
■ Bi-Directional buffers for reduced pin count.
■ 3–5 Volt power supply.
■ Low Power Dissipation;
❐ 3.3 VDC = 30 mW - typical
❐ 5.0 VDC = 100 mW - typical
■ Available in 8 pin SOIC package.
Functional Description
The CYIFS731 is a Frequency Spreading EMI Attenuator
designed for the purpose of reducing Electro Magnetic
Interference (EMI) found in today’s high speed digital systems.
The CYIFS731 uses a proprietary technique to modulate the
output clock, Modout. By modulating the frequency of the digital
clock, measured EMI at the fundamental and harmonic
frequencies is greatly reduced. This reduction in radiated energy
can significantly reduce the cost of complying with regulatory
requirements without degrading digital waveforms.
The CYIFS731 is a very simple device to use and provides 1X
and 2X frequency modulated outputs of the input reference
frequency. By programming the two range select lines, RS0 and
RS1, the CYIFS731 can operate over a very wide range of input
frequencies. By utilizing Bi-Directional Buffer design, the pin
count of the CYIFS731 is kept to a minimum. Bi-Directional
Buffers is a method of providing an input control signal and an
output driver circuit on the same pin. Bi-Directional Buffers is
discussed further on page 6. The CYIFS731 has a simple
frequency selection table that allows it to operate from 4 MHz to
68 MHz in four separate ranges. The bandwidth of the frequency
spread at Modout is determined by the values of the loop filter
components. The modulation rate is determined by the input
frequency and the input frequency range selected. The
bandwidth of the CYIFS731 can be programmed from as little as
0.5% up to as much as 4.0% by selecting the proper loop filter.
It is for this reason that the CYIFS731 uses an external loop filter
(LF), in contrast to an internal loop filter type device which would
severely limit the use of a wide range of bandwidths.
For a complete list of related documentation, click here.
Cypress Semiconductor Corporation • 198 Champion Court
Document Number: 001-73426 Rev. *D
• San Jose, CA 95134-1709 • 408-943-2600
Revised December 16, 2014