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