General Description
The 844S42I is a 3.3V compatible, PLL based clock synthesizer
targeted for clock generation in high-performance instrumentation,
networking and computing applications. Using either the serial (I2C)
or parallel programming interface, the 844S42I enables the
generation of clock frequencies in the range of 81MHz to 2592MHz.
The internal crystal oscillator uses the external quartz crystal as the
basis of its frequency reference. Alternatively, a LVCMOS compatible
clock signal can be used as PLL reference signal. The devices uses
an integer-N synthesizer architecture and is optimized for low-jitter
generation. The VCO within the PLL operates over a range of
1296MHz to 2592MHz. Its output is scaled by a divider that is
configured by either the I2C or parallel interfaces. The crystal
oscillator frequency fXTAL, the PLL pre-divider P, the feedback-divider
M and the PLL post-divider N determine the output frequency. The
feedback path of the PLL is internal.
The PLL post-dividers NA and NB are configured through either the
I
2C or the parallel interfaces, each can provide one of seven division
ratios (1, 2, 3, 4, 6, 8, 16). This divider extends the performance of
the part while providing a typical 50% duty cycle. The high-frequency
outputs QA and QB are differential and are capable of driving a pair
of transmission lines. The positive supply voltage for the internal PLL
is separated from the power supply for the core logic and output
drivers to minimize noise induced jitter. The serial interface is I2C
compatible and provides read and write access to the internal PLL
configuration registers. The lock state of the PLL is indicated by the
LVCMOS-compatible LOCK_DT output. The 844S42I is packaged
in a 8mm x 8mm 56-lead VFQFN package.
Features
• Programmable frequency synthesis optimized for instrumentation,
networking and computing applications
• 81MHz to 2592MHz synthesized clock output signal
• Two differential, universal LVDS or LVPECL compatible
high-frequency outputs
• Output frequency programmable through 2-wire I2C bus or
parallel interface
• On-chip crystal oscillator for reference frequency generation
• Alternative LVCMOS/LVTTL compatible reference clock input
• Clock stop and output enable functionality
• PLL lock indicator output (LVCMOS/LVTTL)
• LVCMOS/LVTTL compatible control inputs
• Fully integrated PLL
• SiGe Technology
• Full 3.3V supply voltage
• -40°C to 85°C ambient operating temperature
• Available in a lead-free (RoHS 6) compliant package