July 2005 ASM5I9658

rev 0.2


Alliance Semiconductor
2575 Augustine Drive • Santa Clara, CA • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com
Notice: The information in this document is subject to change without notice.

3.3V 1:10 LVCMOS PLL Clock Generator

Features
ƒ 1:10 PLL based low-voltage clock generator
ƒ Supports zero-delay operation
ƒ 3.3V power supply
ƒ Generates clock signals up to 250MHz
ƒ Maximum output skew of 120pS
ƒ Differential LVPECL reference clock input
ƒ External PLL feedback
ƒ Drives up to 20 clock lines
ƒ 32 lead LQFP packaging
ƒ Pin and function compatible to the MPC958 and
MPC9658

Functional Description
The ASM5I9658 is a 3.3V compatible, 1:10 PLL based
clock generator and zero-delay buffer targeted for high
performance low-skew clock distribution in mid-range to
high-performance telecom, networking and computing
applications. With output frequencies up to 250MHz and
output skews less than 120pS the device meets the needs
of the most demanding clock applications. The ASM5I9658
is specified for the temperature range of 0°C to +70°C.
The ASM5I9658 utilizes PLL technology to frequency lock
its outputs onto an input reference clock. Normal operation
of the ASM5I9658 requires the connection of the QFB
output to the feedback input to close the PLL feedback path
(external feedback). With the PLL locked, the output
frequency is equal to the reference frequency of the device
and VCO_SEL selects the operating frequency range of 50
to 125MHz or 100 to 250MHz. The two available post-PLL
dividers selected by VCO_SEL (divide-by-2 or divide-by-4)
and the reference clock frequency determines the VCO
frequency. Both must be selected to match the VCO
frequency range. The internal VCO of the ASM5I9658 is
running at either 2x or 4x of the reference clock frequency.
The ASM5I9658 has a differential LVPECL reference input
along with an external feedback input. The ASM5I9658 is
ideal for use as a zero delay, low skew fanout buffer. The
device performance has been tuned and optimized for zero
delay performance.
The PLL_EN and BYPASS controls select the PLL bypass
configuration for test and diagnosis. In this configuration,
the selected input reference clock is bypassing the PLL and
routed either to the output dividers or directly to the
outputs. The PLL bypass configurations are fully static and
the minimum clock frequency specification and all other
PLL characteristics do not apply. The outputs can be
disabled (high-impedance) and the device reset by
asserting the MR/OE pin. Asserting MR/OE also causes the
PLL to loose lock due to missing feedback signal presence
at FB_IN. Deasserting MR/OE will enable the outputs and
close the phase locked loop, enabling the PLL to recover to
normal operation.
The ASM5I9658 is fully 3.3V compatible and requires no
external loop filter components. The inputs (except PCLK)
accept LVCMOS except signals while the outputs provide
LVCMOS compatible levels with the capability to drive
terminated 50Ω transmission lines. For series terminated
transmission lines, each of the ASM5I9658 outputs can
drive one or two traces giving the devices an effective
fanout of 1:16. The device is packaged in a 7x7 mm
2

32-lead LQFP & TQFP Packages.