High-Speed, Low-Skew 1-to-18 Clock Buffer
for Synchronous DRAM (SDRAM) Clock
Buffering Applications
Output Skew, tsk(o), Less Than 250 ps
Pulse Skew, tsk(p), Less Than 500 ps
Supports up to Four Unbuffered SDRAM
Dual Inline Memory Modules (DIMMs)
I2C Serial Interface Provides Individual
Enable Control for Each Output
Operates at 3.3 V
Distributed VCC and Ground Pins Reduce
Switching Noise
100-MHz Operation
ESD Protection Exceeds 2000 V Per
MIL-STD-883, Method 3015
Packaged in 48-Pin Shrink Small Outline
(DL) Package

description
The CDC318A is a high-performance clock buffer
designed to distribute high-speed clocks in PC
applications. This device distributes one input (A)
to 18 outputs (Y) with minimum skew for clock
distribution. The CDC318A operates from a 3.3-V
power supply. It is characterized for operation
from 0°C to 70°C.
This device has been designed with consideration
for optimized EMI performance. Depending on the
application layout, damping resistors in series to
the clock outputs (like proposed in the PC100
specification) may not be needed in most cases.
The device provides a standard mode (100K-bits/s) I2C serial interface for device control. The implementation
is as a slave/receiver. The device address is specified in the I2C device address table. Both of the I2C inputs
(SDATA and SCLOCK) are 5-V tolerant and provide integrated pullup resistors (typically 140 kΩ).
Three 8-bit I2C registers provide individual enable control for each of the outputs. All outputs default to enabled
at powerup. Each output can be placed in a disabled mode with a low-level output when a low-level control bit
is written to the control register. The registers are write only and must be accessed in sequential order (i.e.,
random access of the registers is not supported).
The CDC318A provides 3-state outputs for testing and debugging purposes. The outputs can be placed in a
high-impedance state via the output-enable (OE) input. When OE is high, all outputs are in the operational state.
When OE is low, the outputs are placed in a high-impedance state. OE provides an integrated pullup resistor.