ASM2I9940L Datasheet, PDF (1/13 Pages) Alliance Semiconductor Corporation – Low Voltage 1:18 Clock Distribution Chip

June 2005
ASM2I9940L
rev 1.0
Low Voltage 1:18 Clock Distribution Chip
Features
ƒ LVPECL or LVCMOS Clock Input
ƒ 2.5V LVCMOS Outputs for Pentium II
Microprocessor Support*
ƒ 150pS Maximum Output-to-Output Skew
ƒ Maximum Output Frequency of 250MHz
ƒ 32 Lead LQFP & TQFP Packaging
ƒ Dual or Single Supply Device:
ƒ Dual V_CC Supply Voltage, 3.3V Core and
2.5V Output
ƒ Single 3.3V V_CC Supply Voltage for 3.3V
Outputs
ƒ Single 2.5V V_CC Supply Voltage for 2.5V I/O
ƒ Pin and Function compatible to MPC940L,
MPC9109, CY29940 and CY29940-1
Functional Description
The ASM2I9940L is a 1:18 low Voltage Clock distribution
chip with 2.5V or 3.3V LVCMOS output capabilities. The
device features the capability to select either a differential
LVPECL or LVCMOS compatible input. The 18 outputs are
2.5V or 3.3V LVCMOS compatible and feature the drive
strength to drive 50Ω series or parallel terminated
transmission lines. With output-to-output skews of 150pS,
the ASM2I9940L is ideal as a clock distribution chip for the
most demanding of Synchronous systems. The 2.5V
outputs also make the device ideal for supplying clocks for
a high performance microprocessor based design.
With low output impedance (≈20Ω), in both the HIGH and
LOW logic states, the output buffers of the ASM2I9940L
are ideal for driving series terminated transmission lines.
With a 20Ω output impedance the ASM2I9940L has the
capability of driving two series terminated lines from each
output. This gives the device an effective fanout of 1:36.
The differential LVPECL inputs of the ASM2I9940L allow
the device to interface directly with a LVPECL fanout buffer
to build very wide clock fanout 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_CLK_Sel pin will select the
LVCMOS level clock input. All inputs of the ASM2I9940L
have internal pullup/pulldown resistor, so they can be left
open if unused.
The ASM2I9940L is a single or dual supply device. The
device power supply offers a high degree of flexibility. The
device can operate with a 3.3V core and 3.3V output, a
3.3V core and 2.5V outputs as well as a 2.5V core and
2.5V outputs. The 32-lead LQFP and TQFP Packages
were chosen to optimize performance, board space and
cost of the device. The 32-lead LQFP and TQFP Packages
have a 7x7mm² body size with conservative 0.8mm pin
spacing.
* Pentium II is a trademark of Intel Corporation
Alliance Semiconductor
2575, Augustine Drive • Santa Clara, CA • Tel: [phone] • Fax: [phone] • www.alsc.com
Notice: The information in this document is subject to change without notice.