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Clock Distribution for Intel Microprocessors
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
2.5V Output Capability
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 MPC948L are ideal for driving
series terminated transmission lines. More specifically, each of the 12
MPC948L outputs can drive two series terminated 50鈩?transmission
lines. With this capability, the MPC948L has an effective fanout of 1:24 in
applications where each line drives a single load.
The differential LVPECL inputs of the MPC948L 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 MPC948L 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 MPC948L inputs have internal pullup resistors.
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.
The MPC948L features two independent power supplies; VCCI and VCCO. The VCCI pin powers the internal core logic and
must be tied to 3.3V. The VCCO pin powers the output buffer and can be tied to either 2.5V or 3.3V.
This document contains information on a new product. Specifications and information herein are subject to
change without notice.
4/97
漏
Motorola, Inc. 1997
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