The CY2544 and CY2546 are four-PLL programmable Spread
Spectrum Clock Generators used to reduce EMI found in
high-speed digital electronic systems. Two of the four PLLs
have Spread Spectrum capability. The spread spectrum
feature is turned on or off using the control pin SSON.
The advantage of having four PLLs is that a single device can
generate up to four independent families of frequencies from
a single crystal or reference input frequency. Generally, a
design requires up to four oscillators to achieve the same
result as a single CY2544 or CY2546.
The device uses Cypress proprietary PLL and Spread
Spectrum Clock (SSC) technology to synthesize and modulate
the frequency of the input clock. Frequency modulating the
clock greatly reduces the measured EMI at the fundamental
and harmonic frequencies. This reduction in radiated energy
significantly reduces the cost of complying with regulatory
agency (EMC) requirements and improves time-to-market
without degrading the system performance.
The CY2544 and CY2546 use a factory/field-programmable
configuration memory array to provide customization for
output frequencies, frequency select options, spread characteristics
like spread percentage and modulation frequency,
output drive strength and crystal load capacitance.
Customized devices are configured using CyberClocks?
software or by contacting the factory.
The spread percentage is programmed to either center spread
or down spread with various spread percentages. The range
for center spread is from ±0.125% to ±2.50%. The range for
down spread is from –0.25% to –5.0%. Contact the factory for
smaller or larger spread percentage amounts, if required.
The input to the CY2544 and CY2546 is either a crystal or a
clock signal. The input frequency range for crystals is 8 MHz
to 48 MHz, and for clock signals is 8 MHz to 166 MHz. In
addition, there is a separate input for a clock reference.
The CY2544 and CY2546 have nine clock outputs and each
output has four possible input sources. There are three
frequency select lines FS(2:0) that provide an option to select
eight different sets of frequencies among each of the four
PLLs. Each output has programmable output divider options.
Output 1 has eight possible divider values and outputs 2–9
have four possible divider values for maximum flexibility. The
2-bit or 3-bit output dividers are programmable, providing a
wide output frequency range.
The outputs are glitch-free when frequency is switched using
output dividers. The outputs can have a predictable phase
relationship, if the clock source is the same PLL and divider
values are 2, 3, 4, or 6.
The output banking feature allows the three sets of
frequencies to operate at three different voltages. Selectable
output voltage options are 2.5V, 3.0V, or 3.3V for CY2544 and
1.8V for CY2546 part.
The CY2544 and CY2546 are available in 24-pin QFN
packages with commercial and industrial operating temperature
ranges.