XRK39653_0611 Datasheet, PDF (1/9 Pages) Exar Corporation – 3.3V, 8-OUTPUT ZERO DELAY BUFFER

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NOVEMBER 2006
XRK39653 GENERAL DESCRIPTION
The XRK39653 is a low voltage high performance PLL
based zero delay buffer/clock generator designed for high
speed clock distribution applications. It provides 9 low
skew, low jitter outputs ideal for networking, computing and
telecom applications.
The PLL based design allows the 9 outputs (8 clock outputs
and 1 feedback output) to be phase aligned to the input ref-
erence clock. The outputs source LVCMOS compatible lev-
els and can drive 50Ω transmission lines. If series
termination is used, each output can drive up to 2 lines pro-
viding effectively a fanout of 1:16. The XRK39653’s refer-
ence input accepts a LVPECL clock source.
For normal operation (PLL used to source the outputs), the
feedback output (QFB) is connected to the feedback input
(FB_IN). The VCO range of operation is 200 to 500MHz.
This means that the input/output ranges are determined by
the divider setting. If ÷4 is used, the input/output range is 50
to 125MHz (high range), if ÷8 is used the input/output range
is 25 to 62.5MHz (low range).
For testing purposes two PLL bypass modes are provided.
The first simply replaces the PLL output with the reference
clock (PLL_EN=0, BYPASS=1). The dividers are still in
FIGURE 1. BLOCK DIAGRAM OF THE XRK39653
XRK39653
3.3V, 8-OUTPUT ZERO DELAY BUFFER
REV. 1.0.0
use. The second is a full bypass mode that has the PLL
and divider operation removed (BYPASS=0). In this mode
the reference clock directly sources the outputs drivers.
FEATURES
• 8 LVCMOS Clock Outputs
• 1 Feedback Output
• LVPECL reference clock input
• 25-125 MHz input/output frequency range
■ Input/Output range (÷4): 50-125MHz
■ Input/Output range (÷8): 25-62.5MHz
• 150ps max output to output skew
• Two bypass test mode options
• Fully Integrated PLL
• 3.3V Operation
• Pin compatible with MPC9653
• Industrial temp range: -40°C to +85°C
• 32-Lead TQFP Packaging
VDD
PECL
PECL
FB_IN
VDD
PLL_EN
VCO_SEL
BYPASS
OE
QFB
Q0
0
0
Ref
0
Q1
PLL
1
÷4 1
FB
÷2 1
Q2
Q3
Q4
Q5
Q6
Q7
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com