LCK4950 Datasheet, PDF (1/16 Pages) Agere Systems – Low-Voltage PLL Clock Driver

Data Sheet
November 2001
LCK4950
Low-Voltage PLL Clock Driver
Features
s Fully integrated phase-locked loop (PLL)
s Oscillator or crystal reference input
s Output frequency up to 180 MHz
s Outputs disable in high impedance
s Compatible with PowerPC^®, Intel^®, and high-
performance RISC microprocessors
s TQFP packaging
s Output frequency configurable
s ±35 ps typical cycle-to-cycle jitter
s Pin compatible with the Motorola^® MPC950 clock
driver
Description
The LCK4950 is a PLL-based clock driver device
intended for high-performance clock tree designs.
The LCK4950 is 3.3 V compatible with output
frequencies of up to 180 MHz and output skews of
200 ps. The LCK4950 can accommodate the most
demanding tree designs by employing a fully
differential PLL design. This minimizes cycle-to-cycle
jitter, which is critical when the device is acting as the
reference clock for PLLs in today’s microprocessors
and ASICs. The device has nine low-skew
configurable outputs for support of the clocking
needs of the various high-performance
microprocessors.
To provide input reference clock flexibility, two
selectable division ratios are available on the
LCK4950. The internal VCO runs at either 2x or 4x
the high-speed output. The FBSEL pin is used to
select between a divide by 8 or a divide by 16 of the
VCO frequency to be compared with the input
reference. These selections allow the input reference
to be either one-half, one-fourth, or one-eighth of the
high-speed output.
The LCK4950 is capable of scan clock distribution or
system diagnostics due to an external test clock
input. The REF_SEL pin allows the selection
between a crystal input to an on-chip oscillator for the
reference or selection of a TTL level oscillator input
directly. Only a parallel resonant crystal is required
for the onboard crystal oscillator external
components.
The LCK4950 is fully 3.3 V compatible and requires
no external loop filter components. All inputs accept
LVCMOS or LVTTL compatible levels while the
outputs provide LVCMOS levels with the capability to
drive terminated 50 Ω transmission lines. The
LCK4950 can drive two traces, giving the device an
effective fan out of 1:18 for series-terminated 50 Ω
lines. For optimum performance and board density,
the device is packaged in a 7 mm x 7 mm 32-lead
TQFP package.