July 2005 ASM5I9653A

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 1:8 LVCMOS PLL Clock Generator

Features
ƒ 1:8 PLL based low-voltage clock generator
ƒ Supports zero-delay operation
ƒ 3.3V power supply
ƒ Generates clock signals up to 125MHz
ƒ PLL guaranteed to lock down to 145MHz, output
frequency = 36.25MHz
ƒ Maximum output skew of 150 pS
ƒ Differential LVPECL reference clock input
ƒ External PLL feedback
ƒ Drives up to 16 clock lines
ƒ 32 lead LQFP & TQFP Packages
ƒ Ambient temperature range 0°C to +70°C
ƒ Pin and function compatible to the
MPC953,MPC9653A and MPC9653

Functional Description
The ASM5I9653A utilizes PLL technology to frequency lock
its outputs onto an input reference clock. Normal operation
of the ASM5I9653A 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 25
to 62.5MHz or 50 to 125MHz. The two available post-PLL
dividers selected by VCO_SEL (divide-by-4 or divide-by-8)
and the reference clock frequency determine the VCO
frequency. Both must be selected to match the VCO
frequency range. The internal VCO of the ASM5I9653A is
running at either 4x or 8x of the reference clock frequency.
The ASM5I9653A is guaranteed to lock in a low power PLL
mode in the high frequency range (VCO_SEL = 0) down to
PLL = 145 MHz or Fref = 36.25MHz.
The ASM5I9653A has a differential LVPECL reference
input long with an external feedback input. The device 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 ASM5I9653A 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 ASM5I9653A outputs can drive one or
two traces giving the devices an effective fanout of 1:16.
The device is packaged in a 7x7 mm2 32-lead LQFP &
TQFP Packages.