CYIFS741 Datasheet, PDF (1/19 Pages) Cypress Semiconductor – Reduces Systemic EMI.

CYIFS741
Low EMI Spread Spectrum Clock
Low EMI Spectrum Spread Clock
Features
■ Reduces Systemic EMI.
■ Modulates external clocks including crystals, crystal oscillators
and ceramic resonators.
■ 3–5 Volt power supply.
■ 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.
■ Unmodulated Reference Clock Output.
■ Low Power Dissipation;
❐ 3.3 VDC = 21 mW - typical
❐ 5.0 VDC = 70 mW - typical
■ Available in 8-pin SOIC package.
Functional Description
The CYIFS741 is a frequency spreading EMI attenuator
designed for the purpose of reducing electromagnetic
interference (EMI) found in today’s high speed digital systems.
The CYIFS741 uses a proprietary technique to modulate the
output clock frequency, 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 CYIFS741 is a very simple device to use. By programming
the two range select lines, RS0 and RS1, the CYIFS741 can
operate over a very wide range of input frequencies. By utilizing
bi-directional buffer design, the pin count of the CYIFS741 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
CYIFS741 also provides a buffered reference clock output,
Refout, which can be turned on or off by controlling the Ref_Off
pin. The Refout clock can be used to drive system logic that can
not tolerate frequency spreading, or as a comparison of EMI
reduction with respect to the Modout driver. The CYIFS741 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 CYIFS741 can be programmed from as little as
0.3% up to as much as 4.0% by selecting the proper loop filter.
It is for this reason that the CYIFS741 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.
Cypress Semiconductor Corporation • 198 Champion Court
Document Number: 001-73430 Rev. *A
• San Jose, CA 95134-1709 • 408-943-2600
Revised November 27, 2014