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Clock Distribution for PowerPC鈩?620 L2 Cache
LVPECL or LVCMOS/LVTTL Clock Input
350ps Maximum Output鈥搕o鈥揙utput Skew
Drives Up to 24 Independent Clock Lines
Maximum Output Frequency of 150MHz
Synchronous Output Enable
Tristatable Outputs
32鈥揕ead TQFP Packaging
3.3V VCC Supply Voltage
FA SUFFIX
32鈥揕EAD TQFP PACKAGE
CASE 873A鈥?2
With an output impedance of approximately 7鈩? 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 50鈩?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.
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鈥搇ead TQFP package was chosen to optimize performance, board space and
cost of the device. The 32鈥搇ead TQFP has a 7x7mm body size with a conservative 0.8mm pin spacing.
PowerPC is a trademark of International Business Machines Corporation.
1/97
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Motorola, Inc. 1997
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