IDT5P50901/2/3/4
SPREAD SPECTRUM CLOCK SYNTHESIZER CLOCK SYNTHESIZER
IDT®
SPREAD SPECTRUM CLOCK SYNTHESIZER 3
IDT5P50901/2/3/4 REV F 082112
External Components
Decoupling Capacitor
As with any high-performance mixed-signal IC, the
IDT5P50901/2/3/4 must be isolated from system power
supply noise to perform optimally.
A decoupling capacitor of 0.01µF must be connected
between each VDD and the PCB ground plane.
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50Ω trace (a commonly
used trace impedance), place a 33Ω resistor in series with
the clock line, as close to the clock output pin as possible.
The nominal impedance of the clock output is 20Ω.
External Clock Input
This device operates from an external clock input and as
such does not have a on chip oscillator circuit.
PCB Layout Recommendations
For optimum device performance and lowest output phase
noise, the following guidelines should be observed.
1) The 0.01µF decoupling capacitors should be mounted on
the component side of the board as close to the VDD pin as
possible. No vias should be used between the decoupling
capacitors and VDD pins. The PCB trace to VDD pins
should be kept as short as possible, as should the PCB
trace to the ground via.
2) To minimize EMI, the 33Ω series termination resistor (if
needed) should be placed close to the clock output.
3) An optimum layout is one with all components on the
same side of the board, minimizing vias through other signal
layers. Other signal traces should be routed away from the
IDT5P50901/2/3/4. This includes signal traces just
underneath the device, or on layers adjacent to the ground
plane layer used by the device.
Spread Spectrum Profile
The IDT5P50901/2/3/4 is a low EMI clock generator using
an optimized frequency slew rate algorithm to facilitate down
stream tracking of zero delay buffers and other PLL devices.
The modulation rate is directly relate to the input clock
frequency.
For input frequency ICLK, then use the modulation
frequency indicated for the part below.
Time
Frequency
Modulation Rate
