Description
The PI6C991 is a low-skew, low jitter, 5V phase-lock loop (PLL) programmable skew clock driver, for high performance computing and networking applications. This part offers user selectable skew-control of 4 output pairs, providing the timing delays necessary to optimize high performance clock distribution circuits.
Each output can be hardwired to one of nine delay or function configurations. Delay increments are determined by the input clock frequency and the configurations selected by the user.
The PI6C991 allows the REF clock input to have Spread Spectrum modulation for EMI reduction.
The PI6C991 is pin-compatible with Cypress RoboClock CY7B991, with improved AC/DC characteristics.

Product Features
• Four pairs of programmable skew outputs
• 3.75 to 80 MHz output operation
• User-selectable output functions:
   − Selectable skews
   − Inverted and noninverted
   − Operation at ½ and ¼ input frequency
   − Operation at 2X and 4X input frequency
• Low skew <100ps typical, same pair. 250ps max.
• Allow REF clock input to have Spread Spectrum
   modulation for EMI reduction
• 2X, 4X, ½ and ¼ outputs
• 3-level inputs for skew and output frequency control
• External feedback, internal loop filter
• Low cycle-to-cycle Jitter: <25ps RMS
• Duty cycle of output clock signals: 45% min. 55% max.
• Compatible with Pentium based processor
• Same pinout as Cypress CY7B991
• Packaged in Plastic 32-pin PLCC Package