1. General description
The PCK940L is a 1 : 18 low voltage clock distribution chip with 2.5 V or 3.3 V LVCMOS
output capabilities. The device features the capability to select either a differential
LVPECL or an LVCMOS compatible input. The 18 outputs are 2.5 V or 3.3 V LVCMOS
compatible and feature the drive strength to drive 50 Ω series or parallel terminated
transmission lines. With output-to-output skews of 150 ps, the PCK940L is ideal as a clock
distribution chip for the most demanding of synchronous systems. The 2.5 V outputs also
make the device ideal for supplying clocks for a high performance microprocessor based
design.
With a low output impedance of approximately 20 Ω, in both the HIGH and LOW logic
states, the output buffers of the PCK940L are ideal for driving series terminated
transmission lines. With an output impedance of 20 Ω, the PCK940L has the capability of
driving two series terminated transmission lines from each output. This gives the
PCK940L an effective fan-out of 1 : 36. If a lower output impedance is desired, please see
the PCK942C data sheet.
The differential LVPECL inputs of the PCK940L allow the device to interface directly with a
LVPECL fan-out buffer like the PCKEP111 to build very wide clock fan-out trees or to
couple to a high frequency clock source. The LVCMOS input provides a more standard
interface for applications requiring only a single clock distribution chip at relatively low
frequencies. In addition, the two clock sources can be used to provide for a test clock
interface as well as the primary system clock. A logic HIGH on the LVCMOS_CLKSEL pin
will select the LVCMOS level clock input. All inputs of the PCK940L have internal
pull-up/pull-down resistors so they can be left open if unused.
The PCK940L is a single or dual supply device. The device power supply offers a high
degree of flexibility. The device can operate with a 3.3 V core and 3.3 V output, a 3.3 V
core and 2.5 V outputs, as well as a 2.5 V core and 2.5 V outputs. The 32-lead LQFP
package was chosen to optimize performance, board space and cost of the device. The
32-lead LQFP package has a 7 mm × 7 mm body size with a conservative 0.8 mm pin
spacing.
2. Features
n LVPECL or LVCMOS clock input
n 2.5 V LVCMOS outputs for Pentium II microprocessor support
n 150 ps maximum output-to-output skew
n Maximum output frequency of 250 MHz at 3.3 V V
CC
n 32-lead LQFP packaging
PCK940L
Low voltage 1 : 18 clock distribution chip
Rev. 01 — 4 April 2006 Product data sheet
