SY89473U 
Precision LVPECL 2:1 Multiplexer with 1:2 
Fanout and Internal Termination 
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com 
May 2007 M9999-052207-B
hbwhelp@micrel.com or (408) 955-1690
General Description 
The SY89473U is a 2.5V/3.3V precision, high-speed 2:1 
differential  MUX  capable  of  processing  clocks  up  to 
2.5GHz and data up to 2.5Gbps. 
The  differential  input  includes  Micrel’s  unique,  3-pin 
input  termination  architecture  that  directly  interfaces  to 
any differential  signal (AC-  or  DC-coupled) as small  as 
100mV  (200mVPP)  without  any  level  shifting  or 
termination  resistor  networks  in  the  signal  path.  The 
output  is  800mV,  100K-compatible,  LVPECL  with  fast 
rise/fall times guaranteed to be less than 190ps. 
The  SY89473U  operates  from  a  2.5V  ±5%  or  3.3V 
±10%  supply  and  is  guaranteed  over  the  full  industrial 
temperature range of –40°C to +85°C. The SY89473U is 
part  of  Micrel’s  high-speed,  Precision  Edge® product 
line. For multiple-clock switchover solutions, please refer 
to the SY89840–SY89843U family. 
All support documentation can be found on Micrel’s web 
site at: www.micrel.com. 
Functional Block Diagram 
Precision Edge®
Features
•Selects between two input channels and provides two
copies of the selected output
•Guaranteed AC performance over temperature and
supply voltage:
- DC to 2.5Gbps data throughput
- DC to 2.5GHz fMAX (clock)
- <500ps In-to-Out tpd
- <190ps tr/tf 
- <20ps Output-to-output skew
•Unique patented input isolation design minimizes
crosstalk
•Ultra-low Jitter Design:
- <1psRMS  random jitter
- <1psRMS  cycle-to-cycle jitter
- <10psPP total jitter (clock)
- <0.7psRMS
 crosstalk induced jitter
•Unique patent-pending input termination and VT pin
accepts DC- and AC-coupled inputs (CML, PECL,
LVDS)
•800mV (100K) LVPECL output swing
•2.5V ±5% or 3.3V ±10% supply voltage
•-40°C to +85°C industrial temperature range
•Available in 24-pin (4mm x 4mm) QFN package
Applications 
•Clock switchover
•Data distribution
Markets 
•LAN/WAN
•Enterprise servers
•ATE
•Test and measurement
Precision Edge is a registered trademark of Micrel, Inc.