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MPC948

LOW VOLTAGE 1:12 CLOCK DISTRIBUTION CHIP

Motorola => Freescale 

MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

Low Voltage 1:12 Clock

Distribution Chip

MPC948

The MPC948 is a 1:12 low voltage clock distribution chip. The device

features the capability to select either a differential LVPECL or a LVTTL

compatible input. The 12 outputs are LVCMOS or LVTTL compatible and

feature the drive strength to drive 50Ω series terminated transmission

lines. With output–to–output skews of 350ps, the MPC948 is ideal as a

clock distribution chip for the most demanding of synchronous systems.

For a similar product targeted at a lower price/performance point, please

consult the MPC947 data sheet.

LOW VOLTAGE

1:12 CLOCK

DISTRIBUTION CHIP

• Clock Distribution for PowerPC™ 620 L2 Cache

• LVPECL or LVCMOS/LVTTL Clock Input

• 350ps Maximum Output–to–Output Skew

• Drives Up to 24 Independent Clock Lines

• Maximum Output Frequency of 150MHz

• Synchronous Output Enable

• Tristatable Outputs

• 32–Lead TQFP Packaging

• 3.3V VCC Supply Voltage

With an output impedance of approximately 7Ω, in both the HIGH and

LOW logic states, the output buffers of the MPC948 are ideal for driving

series terminated transmission lines. More specifically, each of the 12

MPC948 outputs can drive two series terminated 50Ω transmission lines.

With this capability, the MPC948 has an effective fanout of 1:24 in

applications where each line drives a single load. With this level of fanout,

the MPC948 provides enough copies of low skew clocks for high

performance synchronous systems, including use as a clock distribution

chip for the L2 cache of a PowerPC 620 based system.

FA SUFFIX

32–LEAD TQFP PACKAGE

CASE 873A–02

The differential LVPECL inputs of the MPC948 allow the device to interface directly with a LVPECL fanout buffer like the

MC100LVE111 to build very wide clock fanout trees or to couple to a high frequency clock source. The LVCMOS/LVTTL 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 TTL_CLK_Sel pin will select the TTL level clock input.

All of the control inputs are LVCMOS/LVTTL compatible. The MPC948 provides a synchronous output enable control to allow

for starting and stopping of the output clocks. A logic high on the Sync_OE pin will enable all of the outputs. Because this control

is synchronized to the input clock, potential output glitching or runt pulse generation is eliminated. In addition, for board level test,

the outputs can be tristated via the tristate control pin. A logic LOW applied to the Tristate input will force all of the outputs into

high impedance. Note that all of the MPC948 inputs have internal pullup resistors.

The MPC948 is fully 3.3V compatible. The 32–lead TQFP package was chosen to optimize performance, board space and

cost of the device. The 32–lead TQFP has a 7x7mm body size with a conservative 0.8mm pin spacing.

PowerPC is a trademark of International Business Machines Corporation.

1/97

© Motorola, Inc. 1997

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