CY2SSTV857-27
Differential Clock Buffer/Driver DDR333/PC2700-Compliant
Features
• Operating frequency: 60 MHz to 200 MHz
• Supports 266, 333 MHz DDR SDRAM
• 10 differential outputs from 1 differential input
• Spread-Spectrum-compatible
• Low jitter (cycle-to-cycle): < 75
• Very low skew: < 100 ps
• Power management control input
• High-impedance outputs when input clock < 10 MHz
• 2.5V operation
• Pin-compatible with CDC857-2 and -3
• 48-pin TSSOP package
• Industrial temp. of
–40°
to +85°C
• Conforms to JEDEC DDR specification
Description
The CY2SSTV857-27 is a high-performance, low-skew,
low-jitter zero-delay buffer designed to distribute differential
clocks in high-speed applications. The CY2SSTV857-27
generates ten differential pair clock outputs from one differ-
ential pair clock input. In addition, the CY2SSTV857-27
features differential feedback clock outputs and inputs. This
allows the CY2SSTV857-27 to be used as a zero-delay buffer.
When used as a zero-delay buffer in nested clock trees, the
CY2SSTV857-27 locks onto the input reference and translates
with near-zero delay to low-skew outputs.
Block Diagram
Pin Configuration
3
2
PD #
AVDD
37
16
T est and
P ow erdo w n
L o gic
5
6
10
9
20
19
22
23
46
47
44
43
Y0
Y0#
Y1
Y1#
Y2
Y2#
Y3
Y3#
Y4
Y4#
Y5
Y5#
Y6
Y6#
Y7
Y7#
Y8
Y8#
Y9
Y9#
FBO UT
FBO U T #
VSS
Y0#
Y0
VDDQ
Y1
Y1#
VSS
VSS
Y2#
Y2
VDDQ
VDDQ
C LK
C LK #
VDDQ
AVDD
AVSS
VSS
Y3#
Y3
VDDQ
Y4
Y4#
VSS
1
2
3
4
5
6
48
47
46
45
44
43
VSS
Y5#
Y5
VDDQ
Y6
Y6#
VSS
VSS
Y7#
Y7
VDDQ
PD#
F B IN
F B IN #
VDDQ
FBOUT#
FBOUT
VSS
Y8#
Y8
VDDQ
Y9
Y9#
VSS
CY2SSTV857-27
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
C LK
C LK#
F B IN
F B IN #
13
14
39
40
PLL
36
35
29
30
27
26
32
33
.......................... Document #: 38-07464 Rev. *F Page 1 of 8
400 West Cesar Chavez, Austin, TX 78701
1+(512) 416-8500
1+(512) 416-9669
www.silabs.com
CY2SSTV857
Pin Description
Pin Number
13, 14
35
36
3, 5, 10, 20, 22
2, 6, 9, 19, 23
27, 29, 39, 44, 46
26, 30, 40, 43, 47
32
Pin Name
CLK, CLK#
FBIN#
FBIN
Y(0:4)
Y#(0:4)
Y(9:5)
Y#(9:5)
FBOUT
I/O
[1]
I
I
I
O
O
O
O
O
Pin Description
Differential Clock Input.
Electrical
Characteristics
LV Differential Input
Feedback Clock Input.
Connect to FBOUT# for accessing the Differential Input
PLL.
Feedback Clock Input.
Connect to FBOUT for accessing the
PLL.
Clock Outputs
Clock Outputs
Clock Outputs
Clock Outputs
Feedback Clock Output.
Connect to FBIN for normal
operation. A bypass delay capacitor at this output will control
Input Reference/Output Clocks phase relationships.
Feedback Clock Output.
Connect to FBIN# for normal
operation. A bypass delay capacitor at this output will control
Input Reference/Output Clocks phase relationships.
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.
2.5V Power Supply for Output Clock Buffers.
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.
Common Ground
Analog Ground
2.5V Nominal
2.5V Nominal
Differential Outputs
Differential Outputs
Differential Outputs
33
FBOUT#
O
37
PD#
I
4, 11,12,15, 21, 28,
34, 38, 45
16
VDDQ
AVDD
1, 7, 8, 18, 24, 25,
31, 41, 42, 48
17
VSS
AVSS
0.0V Ground
0.0V Analog
Ground
When VDDA is strapped LOW, the PLL is turned off and
bypassed for test purposes.
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.
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 (0.1F) 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.
.......................... Document #: 38-07464 Rev. *F Page 2 of 8
CY2SSTV857
Yx
t
C(n)
t
C(n+1)
Figure 3. Cycle-to-cycle Jitter
= 2.5"
DDR _SDRAM
represents a capacitive load
CLK
120
Ohm
CLK#
VTR
FBIN
120
Ohm
FBIN#
FBOUT
FBOUT#
0.3"
VCP
DDR -
SDRAM
120
Ohm
PLL
= 0.6" (Split to Terminator)
DDR -
SDRAM
Output load capacitance for 2 DDR-SDRAM Loads: 5 pF< CL< 8 pF
Figure 4. Clock Structure # 1
= 2.5"
DDR-SDRAM
represents a capacitive load
CLK
120 Ohm
CLK#
PLL
= 0.6" (Split to Terminator)
DDR-SDRAM
DDR-SDRAM
Stack
DDR-SDRAM
VTR
120 Ohm
FBIN
120 Ohm
DDR-SDRAM
VCP
FBIN#
FBOUT
DDR-SDRAM
DDR-SDRAM
Stack
FBOUT#
0.3"
Output load capacitancce for 4 DDR-SDRAM Loads: 10 pF < CL < 16 pF
Figure 5. Clock Structure # 1
.......................... Document #: 38-07464 Rev. *F Page 4 of 8
Embedded System
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