CY2SSTV855
Differential Clock Buffer/Driver
Features
Functional Description
• Phase-locked loop (PLL) clock distribution for Double
Data Rate Synchronous DRAM applications
• 1:5 differential outputs
• External feedback pins (FBINT, FBINC) are used to
synchronize the outputs to the clock input
• SSCG: Spread Aware™ for electromagnetic
interference (EMI) reduction
• 28-pin TSSOP package
The CY2SSTV855 is a high-performance, very-low-skew,
very-low-jitter zero-delay buffer that distributes a differential
clock input pair (SSTL_2) to four differential (SSTL_2) pairs of
clock outputs and one differential pair of feedback clock
outputs. In support of low power requirements, when
power-down is HIGH, the outputs switch in phase and
frequency with the input clock. When power-down is LOW, all
outputs are disabled to a high-impedance state and the PLL is
shut down.
The device supports a low-frequency power-down mode.
When the input is < 20 MHz, the PLL is disabled and the
outputs are put in the Hi-Z state. When the input frequency is
> 20 MHz, the PLL and outputs are enabled.
• Conforms to JEDEC DDR specifications
When AVDD is tied to ground, the PLL is turned off and
bypassed with the input reference clock gated to the outputs.
The Cypress CY2SSTV855 is Spread Aware and supports
tracking of Spread Spectrum clock inputs to reduce EMI
Pin Configuration
Block Diagram
YT0
YC0
PWRDWN
AVDD
Powerdown
and test
logic
YT2
YC2
CLKINT
CLKINC
FBINT
FBINC
PLL
GND
CLKINT
CLKINC
VDDQ
AVDD
AGND
YT3
YC3
FBOUTT
FBOUTC
VDDQ
YT1
YC1
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
CY2SSTV855
YT1
YC1
GND
YC0
YT0
VDDQ
GND
YC3
YT3
VDDQ
PWRDWN
FBINT
FBINC
VDDQ
FBOUTC
FBOUTT
VDDQ
YT2
YC2
GND
28-pin TSSOP
......................... Document #: 38-07459 Rev. *F Page 1 of 6
400 West Cesar Chavez, Austin, TX 78701
1+(512) 416-8500
1+(512) 416-9669
www.silabs.com
CY2SSTV855
Pin Definition[1, 2]
Pin
Name
I/O
Description
6
CLKINT
I
True Clock Input. Low Voltage Differential True Clock Input.
7
CLKINC
I
Complementary Clock Input. Low Voltage Differential Complementary Clock Input.
22
FBINC
I
Feedback Complementary Clock Input. Differential Input Connect to FBOUTC for
accessing the PLL.
23
FBINT
I
Feedback True Clock Input. Differential Input Connect to FBOUTT for accessing the
PLL.
3,12,17,26
YT(0:3)
O
True Clock Outputs. Differential Outputs.
2,13,16,27
YC(0:3)
O
Complementary Clock Outputs. Differential Outputs.
19
FBOUTT
O
Feedback True Clock Output. Differential Outputs. Connect to FBINT for normal
operation. A bypass delay capacitor at this output will control Input Reference/Output
Clocks phase relationships.
20
FBOUTC
O
Feedback Complementary Clock Output. Differential Outputs. Connect to FBINC for
normal operation. A bypass delay capacitor at this output will control Input
Reference/Output Clocks phase relationships.
24
PWRDWN
I
Control input to turn device in the power-down mode.
4,8,11,18,21,25
VDDQ
2.5V Power Supply for Output Clock Buffers.2.5V Nominal.
9
AVDD
2.5V Power Supply for PLL. 2.5V Nominal.
1,5,14,15,28
GND
Ground
10
AGND
Analog Ground. 2.5V Analog Ground.
Zero-delay Buffer
When used as a zero-delay buffer the CY2SSTV855 will likely
be in a nested clock tree application. For these applications
the CY2SSTV855 offers a differential clock input pair as a PLL
reference. The CY2SSTV855 then can lock onto the reference
and translate with near zero delay to low-skew outputs. For
normal operation, the external feedback differential input,
FBINT/C, is connected to the feedback output, FBOUTT/C. 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 AVDD is strapped LOW, the PLL is turned off and
bypassed for test purposes.
Function Table
Inputs
Outputs
AVDD
PWRDWN
CLKINT
CLKINC
YT(0:3)
YC(0:3)
FBOUTT
FBOUTC
PLL
GND
H
L
H
L
H
L
H
BYPASSED/OFF
GND
H
H
L
H
L
H
L
BYPASSED/OFF
2.5V
H
L
H
L
H
L
H
On
2.5V
H
H
L
H
L
H
L
On
2.5V
X
< 20 MHz
< 20 MHz
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Off
Notes:
1. PU = internal pull-up.
2. 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 #: 38-07459 Rev. *F Page 2 of 6
CY2SSTV855
Differential Parameter Measurement Information
CLKINT
CLKINC
FBINT
FBINC
t() n+1
t()n
t()n =
1=N
n
t()n
N (is large number of samples)
N
Figure 1. Static Phase Offset
CLKINT
CLKINC
FBINT
FBINC
td()
t()
td()
td()
Figure 2. Dynamic Phase Offset
Y[0:3], FBOUTT
YC[0:3], FBOUTC
Y[0:3], FBOUTT
YC[0:3], FBOUTC
tsk(o)
Figure 3. Output Skew
......................... Document #: 38-07459 Rev. *F Page 3 of 6
t( )
td()
CY2SSTV855
Differential Parameter Measurement Information (continued)
YT[0:3], FBOUTT
YC[0:3], FBOUTC
t(hper_N+1)
t(hper_n)
1
f(o)
tjit(hper) = thper(n) - 1
2x fo
Figure 4. Half-period Jitter
YT[0:3], FBOUTT
YC[0:3], FBOUTC
t c(n)
t c(n)
tjit(cc) = tc(n)-tc(n+1)
Figure 5. Cycle-to-cycle Jitter
VDD
VDD
V D D /2
16pF
C LKT
60 O hm
VTR
R T = 120 O hm
C LKC
60 O hm
16pF
VCP
V D D /2
Figure 6. Differential Signal Using Direct Termination Resistor
......................... Document #: 38-07459 Rev. *F Page 4 of 6
R e c e iv e r
CY2SSTV855
Absolute Maximum Conditions[3]
Storage Temperature: ................................ –65C to + 150C
This device contains circuitry to protect the inputs against
damage due to high static voltages or electric field; however,
precautions should be taken to avoid application of any
voltage higher than the maximum rated voltages to this circuit.
For proper operation, Vin and Vout should be constrained to the
range:
Operating Temperature:................................ –40C to +85C
VSS < (Vin or Vout) < VDD.
Maximum Power Supply: ................................................ 3.5V
Unused inputs must always be tied to an appropriate logic
voltage level (either VSS or VDD).
Input Voltage Relative to VSS:............................... VSS – 0.3V
Input Voltage Relative to VDDQ or AVDD: ............. VDD + 0.3V
DC Electrical Specifications (AVDD = VDDQ = 2.5V ± 5%, TA = –40°C to +85°C)[4]
Parameter
Description
Conditions
VID
Differential Input Voltage[5]
VIX
Differential Input Crossing Voltage[6] CLKTIN, FBINT
IIN
Input Current
IOL
CLKINT, FBINT
Min.
Typ.
Unit
VDDQ + 0.6
V
(VDDQ/2) –
0.2
VDDQ/2
(VDDQ/2) +
0.2
V
VIN = 0V or VIN = VDDQ, CLKINT,
FBINT
–10
–
10
µA
Output Low Current
VDDQ = 2.375V, VOUT = 1.2V
26
35
–
mA
–18
–32
–
mA
–
0.6
V
1.7
–
–
V
1.1
–
VDDQ – 0.4
V
(VDDQ/2) –
0.2
VDDQ/2
(VDDQ/2) +
0.2
V
10
µA
IOH
Output High Current
VDDQ = 2.375V, VOUT = 1V
VOL
Output Low Voltage
VDDQ = 2.375V, IOL = 12 mA
VOH
Output High Voltage
VDDQ = 2.375V, IOH = –12 mA
Swing[7]
VOUT
Output Voltage
VOC
Output Crossing Voltage[8]
IOZ
High-Impedance Output Current
Current[9]
IDDQ
Dynamic Supply
IDD
PLL Supply Current
Cin
Input Pin Capacitance
VO = GND or VO = VDDQ
0.36
Max.
–10
VDDQ = 170 MHz
–
235
300
mA
AVDD only
–
9
12
mA
–
4
–
pF
Typ.
AC Electrical Specifications (AVDD = VDDQ = 2.5V±5%, TA = –40°C to +85°C)[10, 11]
Parameter
Description
fCLK
Operating Clock Frequency
tDC
Input Clock Duty Cycle[12]
tLOCK
Maximum PLL lock Time
Conditions
AVDD = 2.5V 0.2V
20% to 80% of VOD
Min.
Max.
Unit
60
170
MHz
40
60
%
100
µs
2
V/ns
tSL(O)
Output Clocks Slew Rate
tPZL, tPZH
Output Enable Time (all outputs)[13]
1
30
ns
tPLZ, tPHZ
Output Disable Time (all
outputs)[13]
10
ns
tCCJ
Cycle to Cycle Jitter
f > 66 MHz
–100
100
ps
tJITT(H-PER)
Half-period jitter
f > 66 MHz
–100
100
ps
Notes:
3. Multiple Supplies: The voltage on any input or I/O pin cannot exceed the power pin during power-up. Power supply sequencing is NOT required.
4. Unused inputs must be held HIGH or LOW to prevent them from floating.
5. Differential input signal voltage specifies the differential voltage |VTR – VCP| required for switching, where VTR is the true input level and VCP is the complementary input level.
6. Differential cross-point input voltage is expected to track VDDQ and is the voltage at which the differential signals must be crossing.
7. For load conditions see Figure 6.
8. The value of VOC is expected to be |VTR + VCP|/2. In case of each clock directly terminated by a 120 resistor. See Figure 6.
9. All outputs switching loaded with 16 pF in 60 environment. See Figure 6.
10. Parameters are guaranteed by design and characterization. Not 100% tested in production.
11. PLL is capable of meeting the specified parameters while supporting SSC synthesizers with modulation frequency between 30 kHz and 33.3 kHz with a
downspread of –0.5%
12. While the pulse skew is almost constant over frequency, the duty cycle error increases at higher frequencies. This is due to the formula: duty cycle = tWH/tC,
where the cycle time (tC) decreases as the frequency goes up.
13. Refers to transition of non-inverting output.
14. All differential input and output terminals are terminated with 120/16 pF as shown in Figure 6.
......................... Document #: 38-07459 Rev. *F Page 5 of 6
CY2SSTV85
AC Electrical Specifications (AVDD = VDDQ = 2.5V±5%, TA = –40°C to +85°C)[10, 11] (continued)
Min.
Typ.
Max.
Unit
tPLH
Parameter
Low-to-High Propagation Delay,
CLKINT to YT[0:3]
Description
Conditions
1.5
3.5
6
ns
tPHL
High-to-Low Propagation Delay,
CLKINT to YT[0:3]
1.5
3.5
6
ns
tSK(0)
Any Output to Any Output Skew[14]
–
–
100
ps
Offset[14]
t(Ø)
Static Phase
tD(Ø)
Dynamic Phase Offset
f > 66 MHz
–450
–
450
ps
–350
–
350
ps
Ordering Information
Part Number
Package Type
Product Flow
CY2SSTV855ZC
28-pin TSSOP
Commercial, 0 to 70C
CY2SSTV855ZCT
28-pin TSSOP – Tape and Reel
Commercial, 0 to 70C
CY2SSTV855ZI
28-pin TSSOP
Industrial, –40 to 85C
CY2SSTV855ZIT
28-pin TSSOP – Tape and Reel
Industrial,–40 to 85C
28-pin TSSOP
Commercial, 0 to 70C
Lead Free
CY2SSTV855ZXC
CY2SSTV855ZXCT
28-pin TSSOP – Tape and Reel
Commercial, 0 to 70C
CY2SSTV855ZXI
28-pin TSSOP
Industrial, –40 to 85C
CY2SSTV855ZXIT
28-pin TSSOP – Tape and Reel
Industrial,–40 to 85C
Package Drawing and Dimensions
28-Lead Thin Shrunk Small Outline Package (4.40-mm Body) Z28.173
DIMENSIONS IN MM[INCHES] MIN.
MAX.
PIN 1 ID
1
REFERENCE JEDEC MO-153
PACKAGE WEIGHT 0.16 gms
4.30[0.169]
4.50[0.177]
6.25[0.246]
6.50[0.256]
PART #
Z28.173 STANDARD PKG.
ZZ28.173 LEAD FREE PKG.
28
0.65[0.025]
BSC.
0.19[0.007]
0.30[0.012]
1.10[0.043] MAX.
0.25[0.010]
BSC
GAUGE
PLANE
0°-8°
0.076[0.003]
0.85[0.033]
0.95[0.037]
9.60[0.378]
9.80[0.386]
0.05[0.002]
0.15[0.006]
SEATING
PLANE
0.50[0.020]
0.70[0.027]
0.09[[0.003]
0.20[0.008]
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use of information included herein. Additionally, Silicon Laboratories assumes no responsibility for the functioning of undescribed features or
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......................... Document #: 38-07459 Rev. *F Page 6 of 6