Rev 1.0, November 21, 2006 Page 2 of 8
Zero-delay Buffer
When used as a zero-delay buffer the CY2SSTV857-27 will
likely be in a nested clock tree application. For these applica-
tions the CY2SSTV857-27 offers a differential clock input pair
as a PLL reference. The CY2SSTV857-27 then can lock onto
the reference and translate with near-zero delay to low-skew
outputs. For normal operation, the external feedback input,
FBIN, is connected to the feedback output, FBOUT. By
connecting the feedback output to the feedback input the
propagation delay through the device is eliminated. The PLL
works to align the output edge with the input reference edge
thus producing a near-zero delay. The reference frequency
affects the static phase offset of the PLL and thus the relative
delay between the inputs and outputs.
When VDDA is strapped LOW, the PLL is turned off and
bypassed for test purposes.
Power Management
Output enable/disable control of the CY2SSTV857-27 allows
the user to implement power management schemes into the
design. Outputs are three-stated/disabled when PD# is
asserted low (see Table 1).
Note:
1. A bypass capacitor (0.1µF) should be placed as close as possible to each positive power pin (<0.2”). If these bypass capacitors are not close to the pins, their
high-frequency filtering characteristic will be cancelled by the lead inductance of the traces.
Pin Description
Pin Number Pin Name I/O
[1]
Pin Description
Electrical
Characteristics
13, 14 CLK, CLK# I Differential Clock Input. LV Differential Input
35 FBIN# I Feedback Clock Input. Connect to FBOUT# for accessing the
PLL.
Differential Input
36 FBIN I Feedback Clock Input. Connect to FBOUT for accessing the
PLL.
3, 5, 10, 20, 22 Y(0:4) O Clock Outputs Differential Outputs
2, 6, 9, 19, 23 Y#(0:4) O Clock Outputs
27, 29, 39, 44, 46 Y(9:5) O Clock Outputs Differential Outputs
26, 30, 40, 43, 47 Y#(9:5) O Clock Outputs
32 FBOUT O Feedback Clock Output. Connect to FBIN for normal
operation. A bypass delay capacitor at this output will control
Input Reference/Output Clocks phase relationships.
Differential Outputs
33 FBOUT# O Feedback Clock Output. Connect to FBIN# for normal
operation. A bypass delay capacitor at this output will control
Input Reference/Output Clocks phase relationships.
37 PD# I Power Down# Input. When PD# is set HIGH, all Q and Q#
outputs are enabled and switch at the same frequency as CLK.
When set LOW, all Q and Q# outputs are disabled Hi-Z and the
PLL is powered down.
4, 11,12,15, 21, 28,
34, 38, 45
VDDQ 2.5V Power Supply for Output Clock Buffers. 2.5V Nominal
16 AVDD 2.5V Power Supply for PLL. When VDDA is at GND, PLL is
bypassed and CLK is buffered directly to the device outputs.
During disable (PD# = 0), the PLL is powered down.
2.5V Nominal
1, 7, 8, 18, 24, 25,
31, 41, 42, 48
VSS Common Ground 0.0V Ground
17 AVSS Analog Ground 0.0V Analog
Ground
