CY7B991
CY7B992
Programmable Skew Clock Buffer
Features
Functional Description
■ All output pair skew <100 ps typical (250 maximum)
■ 3.75 to 80 MHz output operation
The CY7B991 and CY7B992 Programmable Skew Clock Buffers
(PSCB) offer user selectable control over system clock functions.
These multiple output clock drivers provide the system integrator
with functions necessary to optimize the timing of high perfor-
mance computer systems. Each of the eight individual drivers,
arranged in four pairs of user controllable outputs, can drive
terminated transmission lines with impedances as low as 50Ω.
They can deliver minimal and specified output skews and full
swing logic levels (CY7B991 TTL or CY7B992 CMOS).
■ User selectable output functions
❐ Selectable skew to 18 ns
❐ Inverted and non-inverted
❐ Operation at 1⁄2 and 1⁄4 input frequency
❐ Operation at 2x and 4x input frequency (input as low as 3.75
MHz)
Each output is hardwired to one of the nine delay or function
configurations. Delay increments of 0.7 to 1.5 ns are determined
by the operating frequency with outputs that skew up to ±6 time
units from their nominal “zero” skew position. The completely
integrated PLL allows cancellation of external load and trans-
mission line delay effects. When this “zero delay” capability of the
PSCB is combined with the selectable output skew functions,
you can create output-to-output delays of up to ±12 time units.
■ Zero input to output delay
■ 50% duty cycle outputs
■ Outputs drive 50Ω terminated lines
■ Low operating current
■ 32-pin PLCC/LCC package
■ Jitter < 200 ps peak-to-peak (< 25 ps RMS)
Divide-by-two and divide-by-four output functions are provided
for additional flexibility in designing complex clock systems.
When combined with the internal PLL, these divide functions
enable distribution of a low frequency clock that are multiplied by
two or four at the clock destination. This facility minimizes clock
distribution difficulty, allowing maximum system clock speed and
flexibility.
Logic Block Diagram
TEST
PHASE
FREQ
DET
FB
VCO AND
TIME UNIT
GENERATOR
FILTER
REF
FS
4Q0
4Q1
4F0
4F1
SELECT
INPUTS
(THREE
LEVEL)
SKEW
3Q0
3F0
3F1
3Q1
SELECT
2Q0
2F0
2F1
MATRIX
2Q1
1Q0
1Q1
1F0
1F1
Cypress Semiconductor Corporation
Document Number: 38-07138 Rev. *B
•
198 Champion Court
•
San Jose, CA 95134-1709
•
408-943-2600
Revised June 22, 2007
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CY7B991
CY7B992
Skew Select Matrix
Block Diagram Description
The skew select matrix contains four independent sections. Each
section has two low skew, high fanout drivers (xQ0, xQ1), and
two corresponding three level function select (xF0, xF1) inputs.
as determined by the function select inputs. All times are
measured with respect to the REF input assuming that the output
Phase Frequency Detector and Filter
The Phase Frequency Detector and Filter blocks accept inputs
from the reference frequency (REF) input and the feedback (FB)
input and generate correction information to control the
frequency of the Voltage Controlled Oscillator (VCO). These
blocks, along with the VCO, form a Phase Locked Loop (PLL)
that tracks the incoming REF signal.
connected to the FB input has 0t selected.
U
Table 2. Programmable Skew Configurations
VCO and Time Unit Generator
Function Selects
Output Functions
The VCO accepts analog control inputs from the PLL filter block.
It generates a frequency used by the time unit generator to
create discrete time units that are selected in the skew select
matrix. The operational range of the VCO is determined by the
1F1,2F1, 1F0,2F0, 1Q0,1Q1,
3F1, 4F1 3F0, 4F0 2Q0, 2Q1
3Q0, 3Q1 4Q0, 4Q1
LOW
LOW
LOW
MID
LOW
MID
–4t
–3t
–2t
–1t
Divide by 2 Divide by 2
U
U
U
U
FS control pin. The time unit (t ) is determined by the operating
–6t
–4t
–2t
–6t
–4t
–2t
U
U
U
U
U
U
U
frequency of the device and the level of the FS pin as shown in
HIGH
LOW
MID
[1]
Table 1. Frequency Range Select and t Calculation
U
MID
0t
0t
0t
U
U
U
f
(MHz)
NOM
MID
HIGH
LOW
MID
+1t
+2t
+3t
+4t
+2t
+4t
+6t
+2t
+4t
+6t
1
Approximate
U
U
U
U
U
U
U
U
U
U
tU = -----------------------
FS
Frequency(MHz)At
fNOM × N
HIGH
HIGH
HIGH
Min Max
Which t = 1.0 ns
U
where N =
LOW
MID
15
25
40
30
50
80
44
26
16
22.7
38.5
62.5
HIGH
Divide by 4 Inverted
HIGH
Notes
1. For all tri-state inputs, HIGH indicates a connection to VCC, LOW indicates a connection to GND, and MID indicates an open connection. Internal termination circuitry
holds an unconnected input to VCC/2.
2. The level is set on FS is determined by the “normal” operating frequency (fNOM) of the VCO and Time Unit Generator (see Logic Block Diagram). Nominal frequency
(fNOM) always appears at 1Q0 and the other outputs when they are operated in their undivided modes (see Table 2). The frequency appearing at the REF and FB
inputs are fNOM when the output connected to FB is undivided. The frequency of the REF and FB inputs are fNOM/2 or fNOM/4 when the part is configured for a
frequency multiplication by using a divided output as the FB input.
3. When the FS pin is selected HIGH, the REF input must not transition upon power up until VCC has reached 4.3V.
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Figure 1 shows the typical outputs with FB connected to a zero skew output.
Figure 1. Typical Outputs with FB Connected to a Zero-Skew Output
FBInput
REFInput
1Fx
2Fx
3Fx
4Fx
(N/A)
LM
– 6t
– 4t
– 3t
U
U
U
LL
LH
LM
(N/A)
LH
ML
ML
– 2t
– 1t
U
U
(N/A)
MM
MH
HL
MM
(N/A)
MH
0t
U
U
U
U
+1t
+2t
+3t
HM
(N/A)
HH
HL
HM
+4t
+6t
U
U
(N/A)
(N/A)
(N/A)
LL/HH
HH
DIVIDED
INVERT
Test Mode
The TEST input is a three level input. In normal system
operation, this pin is connected to ground, enabling the
CY7B991 or CY7B992 to operate as explained in “Skew Select
inputs can have a removable jumper to ground, or be tied LOW
through a 100Ω resistor. This enables an external tester to
change the state of these pins.
If the TEST input is forced to its MID or HIGH state, the device
operates with its internal phase locked loop disconnected, and
input levels supplied to REF directly controls all outputs. Relative
output to output functions are the same as in normal mode.
In contrast with normal operation (TEST tied LOW), all outputs
function based only on the connection of their own function
selects inputs (xF0 and xF1) and the waveform characteristics of
the REF input.
Note
4. FB connected to an output selected for “zero” skew (i.e., xF1 = xF0 = MID).
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Maximum Ratings
Operating Range
Operating outside these boundaries affects the performance and
life of the device. These user guidelines are not tested.
Ambient
Temperature
Range
V
CC
Storage Temperature .................................–65°C to +150°C
Ambient Temperature with
Power Applied ............................................–55°C to +125°C
Supply Voltage to Ground Potential................–0.5V to +7.0V
DC Input Voltage ............................................–0.5V to +7.0V
Output Current into Outputs (LOW)............................. 64 mA
Commercial
0°C to +70°C
5V ± 10%
5V ± 10%
5V ± 10%
5V ± 10%
Industrial
–40°C to +85°C
–55°C to +125°C
–55°C to +125°C
[5]
Military
[5]
Military
Static Discharge Voltage............................................>2001V
(MIL-STD-883, Method 3015)
Latch Up Current .....................................................>200 mA
Note
5. Indicates case temperature.
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Electrical Characteristics
Over the Operating Range
CY7B991
CY7B992
Min Max
Parameter
Description
Test Conditions
= Min I = –16 mA
Min
Max
Unit
V
Output HIGH Voltage
V
V
V
V
2.4
V
OH
CC
CC
CC
CC
OH
= Min, I =–40 mA
V
–0.75
OH
CC
V
Output LOW Voltage
= Min, I = 46 mA
0.45
V
OL
OL
= Min, I = 46 mA
0.45
OL
V
V
V
V
V
I
Input HIGH Voltage
(REF and FB inputs only)
2.0
V
V
1.35
–
V
CC
V
V
IH
CC
CC
Input LOW Voltage
(REF and FB inputs only)
–0.5
0.8
–0.5
1.35
IL
Three Level Input HIGH
Voltage (Test, FS, xFn)
Min ≤ V ≤ Max
V
– 0.85
V
V
– 0.85
V
V
IHH
IMM
ILL
CC
CC
CC
CC
CC
Three Level Input MID
Voltage (Test, FS, xFn)
Min ≤ V ≤ Max
V
/2 –
V
/2 +
V
/2 –
V /2 +
CC
500 mV
V
CC
CC
CC
500 mV
CC
500 mV
500 mV
Three Level Input LOW
Voltage (Test, FS, xFn)
Min ≤ V
≤
0.0
0.85
0.0
0.85
V
CC
Maximum
InputHIGHLeakageCurrent
(REF and FB inputs only)
V
V
V
V
V
V
= Max, V = Max.
10
10
μA
μA
μA
μA
μA
mA
mA
IH
CC
CC
IN
IN
I
I
I
I
I
I
Input LOW Leakage Current
(REF and FB inputs only)
= Max, V = 0.4V
–500
–50
–500
–50
IL
IN
Input HIGH Current
(Test, FS, xFn)
= V
200
50
200
50
IHH
IMM
ILL
CC
Input MID Current
(Test, FS, xFn)
= V /2
IN
CC
Input LOW Current
(Test, FS, xFn)
= GND
–200
–250
–200
N/A
IN
Output Short Circuit
= Max, V
OUT
OS
CC
Current
= GND (25°C only)
Operating Current Used by
Internal Circuitry
V
=V
=Max, Com’l
85
90
85
90
CCQ
CCN
CCQ
All Input
Selects Open
Mil/Ind
I
Output Pair
V
= V = Max,
CCQ
= 0 mA
14
19
mA
CCN
CCN
I
OUT
Input Selects Open, f
MAX
PD
Output Pair
V
= V
= 0 mA
= Max,
78
104[11]
mW
CCN
CCQ
I
OUT
Input Selects Open, f
MAX
Notes
7. These inputs are normally wired to V , GND, or left unconnected (actual threshold voltages vary as a percentage of V ). Internal termination resistors hold
CC
CC
unconnected inputs at V /2. If these inputs are switched, the function and timing of the outputs may glitch and the PLL may require an additional t
CC
time before
LOCK
all datasheet limits are achieved.
8. CY7B991 must be tested one output at a time, output shorted for less than one second, less than 10% duty cycle. Room temperature only. CY7B992 outputs must
not be shorted to GND. Doing so may cause permanent damage.
9. Total output current per output pairis approximated by the following expression that includes device current plus load current:
CY7B991:
CY7B992:
Where
I
I
= [(4 + 0.11F) + [((835 – 3F)/Z) + (.0022FC)]N] x 1.1
= [(3.5+ 0.17F) + [((1160 – 2.8F)/Z) + (.0025FC)]N] x 1.1
CCN
CCN
F = frequency in MHz; C = capacitive load in pF; Z = line impedance in ohms; N = number of loaded outputs; 0, 1, or 2; FC = F < C.
10. Total power dissipation per output pair can be approximated by the following expression that includes device power dissipation plus power dissipation due to the load
circuit:
CY7B991:PD = [(22 + 0.61F) + [((1550 – 2.7F)/Z) + (.0125FC)]N] x 1.1
CY7B992:PD = [(19.25+ 0.94F) + [((700 + 6F)/Z) + (.017FC)]N] x 1.1
11. Applies to REF and FB inputs only. Tested initially and after any design or process changes that may affect these parameters.
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Capacitance
CMOS output buffer current and power dissipation specified at 50 MHz reference frequency.
Parameter
Description
Test Conditions
Max
Unit
C
Input Capacitance
T = 25°C, f = 1 MHz, V = 5.0V
10
pF
IN
A
CC
AC Test Loads and Waveforms
5V
3.0V
2.0V
=1.5V
0.8V
0.0V
2.0V
=1.5V
0.8V
R1=130
R2=91
R1
R2
V
th
V
th
C = 50 pF (C =30 pF for –2 and –5 devices)
L
L
C
L
(Includes fixture and probe capacitance)
≤1ns
≤1ns
TTL ACTest Load (CY7B991)
TTL Input Test Waveform (CY7B991)
V
CC
V
CC
R1=100
R2=100
80%
CC
20%
0.0V
80%
= V /2
20%
R1
=30 pF for –2 and –5 devices)
C = 50 pF (C
L
L
V
th
= V /2
V
th
CC
(Includes fixture and probe capacitance)
C
L
R2
≤3ns
≤3ns
CMOS AC Test Load (CY7B992)
CMOS Input Test Waveform (CY7B992)
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Switching Characteristics Over the Operating Range
CY7B991–2
CY7B992–2
Parameter
Description
FS = LOW
Min
15
Typ
Max
Min
Typ
Max
Unit
f
Operating Clock
30
50
80
15
30
50
MHz
NOM
Frequency in MHz
FS = MID
25
40
25
40
FS = HIGH
80
t
t
t
t
REF Pulse Width HIGH
REF Pulse Width LOW
Programmable Skew Unit
5.0
5.0
5.0
ns
ns
RPWH
RPWL
U
5.0
0.05
0.20
0.05
0.20
ns
SKEWPR
(XQ0, XQ1)
t
t
Zero Output Skew (All Outputs)
0.1
0.25
0.5
0.1
0.25
0.5
ns
ns
SKEW0
SKEW1
0.25
0.25
Class Outputs)
t
t
t
Divided-Divided)
0.3
0.25
0.5
0.5
0.5
0.9
0.3
0.25
0.5
0.5
0.5
0.7
ns
ns
ns
SKEW2
SKEW3
SKEW4
Class Outputs)
Divided-Inverted)
t
t
t
t
t
t
t
t
t
Device-to-Device Skew
0.75
+0.25
+0.65
2.0
0.75
+0.25
+0.5
3.0
ns
ns
ns
ns
ns
ns
ns
ms
ps
ps
DEV
Propagation Delay, REF Rise to FB Rise
–0.25
–0.65
0.0
0.0
–0.25
–0.5
0.0
0.0
PD
Output Duty Cycle Variation
ODCV
PWH
PWL
ORISE
OFALL
LOCK
JR
Output HIGH Time Deviation from 50%
Output LOW Time Deviation from 50%
1.5
3.0
Output Rise Time
0.15
0.15
1.0
1.0
1.2
0.5
0.5
2.0
2.0
2.5
Output Fall Time
1.2
2.5
PLL Lock Time
0.5
0.5
Cycle-to-Cycle Output
Jitter
RMS
25
25
Peak-to-Peak
200
200
Notes
12. CMOS output buffer current and power dissipation specified at 50 MHz reference frequency.
13. Test measurement levels for the CY7B991 are TTL levels (1.5V to 1.5V). Test measurement levels for the CY7B992 are CMOS levels (VCC/2 to VCC/2). Test
conditions assume signal transition times of 2 ns or less and output loading as shown in the AC Test Loads and Waveforms unless otherwise specified.
14. Guaranteed by statistical correlation. Tested initially and after any design or process changes that affect these parameters.
15. Except as noted, all CY7B992–2 and –5 timing parameters are specified to 80 MHz with a 30 pF load.
16. SKEW is defined as the time between the earliest and the latest output transition among all outputs for which the same tU delay is selected when all are loaded
with 50 pF and terminated with 50Ω to 2.06V (CY7B991) or VCC/2 (CY7B992).
17. tSKEWPR is defined as the skew between a pair of outputs (XQ0 and XQ1) when all eight outputs are selected for 0tU.
18. tSKEW0 is defined as the skew between outputs when they are selected for 0tU. Other outputs are divided or inverted but not shifted.
19. CL=0 pF. For CL=30 pF, tSKEW0=0.35 ns.
20. There are three classes of outputs: Nominal (multiple of tU delay), Inverted (4Q0 and 4Q1 only with 4F0 = 4F1 = HIGH), and Divided (3Qx and 4Qx only in
Divide-by-2 or Divide-by-4 mode).
21. tDEV is the output-to-output skew between any two devices operating under the same conditions (VCC ambient temperature, air flow, and so on.)
22. tODCV is the deviation of the output from a 50% duty cycle. Output pulse width variations are included in tSKEW2 and tSKEW4 specifications.
23. Specified with outputs loaded with 30 pF for the CY7B99X–2 and –5 devices and 50 pF for the CY7B99X–7 devices. Devices are terminated through 50Ω to
2.06V (CY7B991) or VCC/2 (CY7B992).
24. tPWH is measured at 2.0V for the CY7B991 and 0.8 VCC for the CY7B992. tPWL is measured at 0.8V for the CY7B991 and 0.2 VCC for the CY7B992.
25. tORISE and tOFALL measured between 0.8V and 2.0V for the CY7B991 or 0.8VCC and 0.2VCC for the CY7B992.
26. tLOCK is the time that is required before synchronization is achieved. This specification is valid only after VCC is stable and within normal operating limits.
This parameter is measured from the application of a new signal or frequency at REF or FB until tPD is within specified limits.
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Switching Characteristics
Over the Operating Range
(continued)
CY7B991–5
Typ
CY7B992–5
Typ
Parameter
Description
FS = LOW
Min
15
Max
30
Min
15
Max
30
Unit
f
Operating Clock
MHz
NOM
Frequency in MHz
FS = MID
25
50
25
50
FS = HIGH
40
80
40
80
t
t
t
t
REF Pulse Width HIGH
REF Pulse Width LOW
Programmable Skew Unit
5.0
5.0
5.0
5.0
ns
ns
RPWH
RPWL
U
0.1
0.25
0.1
0.25
ns
SKEWPR
(XQ0, XQ1)
t
t
Zero Output Skew (All Outputs)
0.25
0.6
0.5
0.7
0.25
0.6
0.5
0.7
ns
ns
SKEW0
SKEW1
Class Outputs)
t
t
t
Divided-Divided)
0.5
0.5
0.5
1.0
0.7
1.0
0.6
0.5
0.6
1.5
0.7
1.7
ns
ns
ns
SKEW2
SKEW3
SKEW4
Class Outputs)
Divided-Inverted)
t
t
t
t
t
t
t
t
t
Device-to-Device Skew
1.25
+0.5
+1.0
2.5
3
1.25
+0.5
+1.2
4.0
ns
ns
ns
ns
ns
ns
ns
ms
ps
ps
DEV
Propagation Delay, REF Rise to FB Rise
–0.5
–1.0
0.0
0.0
–0.5
–1.2
0.0
0.0
PD
Output Duty Cycle Variation
ODCV
PWH
PWL
ORISE
OFALL
LOCK
JR
Output HIGH Time Deviation from 50%
Output LOW Time Deviation from 50%
4.0
Output Rise Time
0.15
0.15
1.0
1.0
1.5
1.5
0.5
25
0.5
0.5
2.0
2.0
3.5
Output Fall Time
3.5
[26]
PLL Lock Time
0.5
Cycle-to-Cycle Output
Jitter
RMS
25
[14]
Peak-to-Peak
200
200
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Switching Characteristics
Over the Operating Range
(continued)
CY7B991–7
Typ
CY7B992–7
Typ
Parameter
Description
Operating Clock FS = LOW
Min
15
Max
30
Min
15
Max
30
Unit
f
MHz
NOM
Frequency in MHz
FS = MID
25
50
25
50
FS = HIGH
40
80
40
80
t
t
t
t
REF Pulse Width HIGH
REF Pulse Width LOW
Programmable Skew Unit
5.0
5.0
5.0
5.0
ns
ns
RPWH
RPWL
U
0.1
0.25
0.1
0.25
ns
SKEWPR
(XQ0, XQ1)
t
t
Zero Output Skew (All Outputs)
0.3
0.6
0.75
1.0
0.3
0.6
0.75
1.0
ns
ns
SKEW0
SKEW1
Class Outputs)
t
t
t
Divided-Divided)
1.0
0.7
1.2
1.5
1.2
1.7
1.0
0.7
1.2
1.5
1.2
1.7
ns
ns
ns
SKEW2
SKEW3
SKEW4
Class Outputs)
Divided-Inverted)
t
t
t
t
t
t
t
t
t
Device-to-Device Skew
1.65
+0.7
+1.2
3
1.65
+0.7
+1.5
5.5
ns
ns
ns
ns
ns
ns
ns
ms
ps
ps
DEV
Propagation Delay, REF Rise to FB Rise
–0.7
–1.2
0.0
0.0
–0.7
–1.5
0.0
0.0
PD
Output Duty Cycle Variation
ODCV
PWH
PWL
ORISE
OFALL
LOCK
JR
Output HIGH Time Deviation from 50%
Output LOW Time Deviation from 50%
3.5
2.5
2.5
0.5
25
5.5
Output Rise Time
0.15
0.15
1.5
1.5
0.5
0.5
3.0
3.0
5.0
Output Fall Time
5.0
PLL Lock Time
0.5
Cycle-to-Cycle Output
Jitter
RMS
25
[14]
Peak-to-Peak
200
200
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
AC Timing Diagrams
t
t
RPWL
REF
t
RPWH
REF
t
t
ODCV
PD
t
ODCV
FB
Q
t
JR
t
t
t
t
SKEWPR,
SKEW0,1
SKEWPR,
SKEW0,1
OTHERQ
t
SKEW2
t
SKEW2
INVERTED Q
t
SKEW3,4
t
t
SKEW3,4
t
SKEW3,4
REF DIVIDED BY 2
REF DIVIDED BY 4
t
SKEW1,3, 4
SKEW2,4
Document Number: 38-07138 Rev. *B
Page 11 of 19
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CY7B991
CY7B992
Operational Mode Descriptions
Figure 2. Zero Skew and Zero Delay Clock Driver
REF
LOAD
Z
Z
0
L1
L2
FB
SYSTEM
CLOCK
REF
FS
LOAD
LOAD
4Q0
4Q1
4F0
4F1
0
3Q0
3Q1
3F0
3F1
L3
L4
2F0
2F1
2Q0
2Q1
Z
0
1F0
1F1
1Q0
1Q1
LOAD
TEST
Z
0
LENGTH L1 = L2 = L3 = L4
Figure 2 shows the PSCB configured as a zero skew clock buffer. In this mode the 7B991/992 is used as the basis for a low-skew
clock distribution tree. When all of the function select inputs (xF0, xF1) are left open, the outputs are aligned and each drives a
terminated transmission line to an independent load. The FB input is tied to any output in this configuration and the operating frequency
range is selected with the FS pin. The low-skew specification, coupled with the ability to drive terminated transmission lines (with
impedances as low as 50 ohms), enables efficient printed circuit board design.
Figure 3. Programmable Skew Clock Driver
REF
LOAD
Z
0
L1
L2
FB
REF
FS
SYSTEM
CLOCK
LOAD
LOAD
4Q0
4Q1
4F0
4F1
Z
0
3Q0
3Q1
3F0
3F1
L3
L4
2F0
2F1
2Q0
2Q1
Z
0
1F0
1F1
1Q0
1Q1
LOAD
TEST
Z
0
LENGTH L1 = L2
L3 < L2 by 6 inches
L4 > L2 by 6 inches
Figure 3 shows a configuration to equalize skew between metal
traces of different lengths. In addition to low skew between
outputs, the PSCB is programmed to stagger the timing of its
outputs. Each of the four groups of output pairs are programmed
to different output timing. Skew timing is adjusted over a wide
range in small increments with the appropriate strapping of the
function select pins. In this configuration the 4Q0 output is fed
back to FB and configured for zero skew. The other three pairs
of outputs are programmed to yield different skews relative to the
feedback. By advancing the clock signal on the longer traces or
retarding the clock signal on shorter traces, all loads can receive
the clock pulse at the same time.
In this illustration the FB input is connected to an output with 0-ns
skew (xF1, xF0 = MID) selected. The internal PLL synchronizes
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
F
the FB and REF inputs and aligns their rising edges to ensure
that all outputs have precise phase alignment.
Figure 5. Frequency Multiplier with Skew Connectrions
Clock skews are advanced by ±6 time units (tU) when using an
output selected for zero skew as the feedback. A wider range of
delays is possible if the output connected to FB is also skewed.
Since “Zero Skew”, +tU, and –tU are defined relative to output
groups, and since the PLL aligns the rising edges of REF and
FB, you can create wider output skews by proper selection of the
xFn inputs. For example, a +10 tU between REF and 3Qx is
achieved by connecting 1Q0 to FB and setting 1F0 = 1F1 = GND,
3F0 = MID, and 3F1 = High. (Since FB aligns at –4 tU and 3Qx
skews to +6 tU, a total of +10 tU skew is realized.) Many other
configurations are realized by skewing both the outputs used as
the FB input and skewing the other outputs.
REF
FB
20 MHz
REF
FS
40 MHz
4Q0
4Q1
4F0
4F1
20 MHz
80 MHz
3Q0
3Q1
3F0
3F1
2F0
2F1
2Q0
2Q1
1Q0
1Q1
1F0
1F1
Figure 4. Inverted Output Connections
TEST
REF
Figure 5 shows the PSCB configured as a clock multiplier. The
3Q0 output is programmed to divide by four and is sent to FB.
This causes the PLL to increase its frequency until the 3Q0 and
3Q1 outputs are locked at 20 MHz while the 1Qx and 2Qx
outputs run at 80 MHz. The 4Q0 and 4Q1 outputs are
programmed to divide by two, that results in a 40 MHz waveform
at these outputs. Note that the 20 and 40 MHz clocks fall simul-
taneously and are out of phase on their rising edge. This enables
FB
REF
FS
4Q0
4Q1
4F0
4F1
1
1
the designer to use the rising edges of the ⁄ frequency and ⁄
2
4
3Q0
3Q1
3F0
3F1
frequency outputs without concern for rising edge skew. The
2Q0, 2Q1, 1Q0, and 1Q1 outputs run at 80 MHz and are skewed
by programming their select inputs accordingly. Note that the FS
pin is wired for 80 MHz operation because that is the frequency
of the fastest output.
2Q0
2Q1
2F0
2F1
1Q0
1Q1
1F0
1F1
TEST
Figure 6. Frequency Divider Connections
REF
Figure 4 shows an example of the invert function of the PSCB.
In this example the 4Q0 output used as the FB input is
programmed for invert (4F0 = 4F1 = HIGH) while the other three
pairs of outputs are programmed for zero skew. When 4F0 and
4F1 are tied high, 4Q0 and 4Q1 become inverted zero phase
outputs. The PLL aligns the rising edge of the FB input with the
rising edge of the REF. This causes the 1Q, 2Q, and 3Q outputs
to become the “inverted” outputs with respect to the REF input.
It is possible to have 2 inverted and 6 non-inverted outputs or 6
inverted and 2 non-inverted outputs by selecting the output
connected to FB. The correct configuration is determined by the
need for more (or fewer) inverted outputs. 1Q, 2Q, and 3Q
outputs can also be skewed to compensate for varying trace
delays independent of inversion on 4Q.
FB
REF
FS
20 MHz
10 MHz
4Q0
4F0
4Q1
4F1
5 MHz
3Q0
3Q1
3F0
3F1
20 MHz
2Q0
2Q1
2F0
2F1
1F0
1F1
1Q0
1Q1
TEST
Figure 6 demonstrates the PSCB in a clock divider application.
2Q0 is fed back to the FB input and programmed for zero skew.
3Qx is programmed to divide by four. 4Qx is programmed to
divide by two. Note that the falling edges of the 4Qx and 3Qx
outputs are aligned. This enables the use of rising edges of the
1
1
⁄
frequency and
⁄
frequency without concern for skew
2
4
mismatch. The 1Qx outputs are programmed to zero skew and
are aligned with the 2Qx outputs. In this example, the FS input
is grounded to configure the device in the 15 MHz to 30 MHz
Document Number: 38-07138 Rev. *B
Page 13 of 19
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CY7B991
CY7B992
range since the highest frequency output is running at 20 MHz.
Figure 7 shows some of the functions that are selectable on the
3Qx and 4Qx outputs. These include inverted outputs and
outputs that offer divide-by-2 and divide-by-4 timing. An inverted
output enables the system designer to clock different
subsystems on opposite edges, without suffering from the pulse
asymmetry typical of non-ideal loading. This function enables
each of the two subsystems to clock 180 degrees out of phase
and align within the skew specifications.
of the divider adds to the skew between the different clock
signals.
These divided outputs, coupled with the Phase Locked Loop,
enables the PSCB to multiply the clock rate at the REF input by
either two or four. This mode enables the designer to distribute
a low frequency clock between various portions of the system,
and then locally multiply the clock rate to a more suitable
frequency, still maintaining the low skew characteristics of the
clock driver. The PSCB performs all of the functions described in
this section at the same time. It multiplies by two and four or
divides by two (and four) at the same time. In other words, it is
shifting its outputs over a wide range or maintaining zero skew
between selected outputs.
The divided outputs offer a zero delay divider for portions of the
system that need the clock divided by either two or four, and still
remain within a narrow skew of the “1X” clock. Without this
feature, an external divider is added, and the propagation delay
Figure 7. Multi-Function Clock Driver
REF
LOAD
Z
0
80 MHz
INVERTED
FB
REF
FS
20 MHz
DISTRIBUTION
CLOCK
LOAD
LOAD
4Q0
4Q1
4F0
4F1
20 MHz
Z
0
3Q0
3Q1
2Q0
2Q1
3F0
3F1
2F0
2F1
80 MHz
ZERO SKEW
Z
0
1Q0
1Q1
1F0
LOAD
80 MHz
SKEWED –3.125 ns (–4tU)
1F1
TEST
Z
0
Document Number: 38-07138 Rev. *B
Page 14 of 19
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CY7B991
CY7B992
Figure 8. Board-to-Board Clock Distribution
LOAD
LOAD
REF
Z
0
L1
FB
SYSTEM
CLOCK
REF
FS
4F0
4F1
L2
Z
0
4Q0
4Q1
3Q0
3Q1
3F0
3F1
LOAD
L3
2F0
2F1
2Q0
2Q1
Z
0
1F0
1F1
1Q0
1Q1
L4
FB
REF
TEST
FS
LOAD
4Q0
4Q1
3Q0
3Q1
2Q0
2Q1
1Q0
1Q1
4F0
4F1
3F0
3F1
2F0
2F1
1F0
1F1
TEST
Z
0
LOAD
Figure 8 shows the CY7B991 and 992 connected in series to construct a zero skew clock distribution tree between boards. Delays
of the downstream clock buffers are programmed to compensate for the wire length (that is, select negative skew equal to the wire
delay) necessary to connect them to the master clock source, approximating a zero delay clock tree. Cascaded clock buffers accumu-
lates low frequency jitter because of the non-ideal filtering characteristics of the PLL filter. Do not connect more than two clock buffers
in series.
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Ordering Information
Accuracy
Ordering Code
(ps)
Operating
Range
Package Type
32-Pb Plastic Leaded Chip Carrier
250
CY7B991–2JC
CY7B991–2JCT
CY7B991–5JC
CY7B991–5JCT
CY7B991–5JI
Commercial
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
Commercial
Commercial
Commercial
Industrial
500
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
CY7B991–5JIT
CY7B991–7JC
CY7B991–7JCT
CY7B991–7JI
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
Industrial
750
Commercial
Commercial
Industrial
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
CY7B991–7LMB
CY7B992–2JC
CY7B992–2JCT
CY7B992–5JC
CY7B992–5JCT
32-Pin Rectangular Leadless Chip Carrier
32-Pb Plastic Leaded Chip Carrier
Military
250
500
Commercial
Commercial
Commercial
Commercial
Industrial
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
[27]
CY7B992–5JI
CY7B992–5JIT
CY7B992–7JC
CY7B992–7JCT
CY7B992–7JI
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
Industrial
750
Commercial
Commercial
Industrial
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
CY7B992–7LMB
32-Pin Rectangular Leadless Chip Carrier
Military
Pb-Free
250
CY7B991–2JXC
32-Pb Plastic Leaded Chip Carrier
Commercial
Commercial
Commercial
Commercial
Industrial
CY7B991–2JXCT
CY7B991–5JXC
CY7B991–5JXCT
CY7B991–5JXI
CY7B991–5JXIT
CY7B991–7JXC
CY7B991–7JXCT
CY7B992–5JXI
CY7B992–5JXIT
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
500
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
Industrial
750
500
Commercial
Commercial
Industrial
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
32-Pb Plastic Leaded Chip Carrier
32-Pb Plastic Leaded Chip Carrier - Tape and Reel
Industrial
Note
27. Not recommended for the new design.
Document Number: 38-07138 Rev. *B
Page 16 of 19
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CY7B991
CY7B992
Military Specifications
Group A Subgroup Testing
DC Characteristics
Parameter
Subgroups
V
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
OH
V
OL
V
IH
V
IL
V
IHH
V
IMM
V
ILL
I
IH
I
IL
I
IHH
I
IMM
I
ILL
I
CCQ
I
CCN
Package Diagrams
Figure 9. 32-Pin Plastic Leaded Chip Carrier
51-85002-*B
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Package Diagrams (continued)
Figure 10. 32-Pin Rectangular Leadless Chip Carrier
MIL-STD-1835 C-12
51-85002-*B
Document Number: 38-07138 Rev. *B
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CY7B991
CY7B992
Document History
Document Title: CY7B991/CY7B992 Programmable Skew Clock Buffer
Document Number: 38-07138
Orig. of
Change
REV.
ECN NO. Issue Date
Description of Change
**
110247
12/19/01
SZV
Change from Specification number: 38-00513 to 38-07138
*A
1199925
See ECN KVM/AESA Add Pb-free part numbers. Update package names in Ordering Information
table. Remove Pentium reference on page 1.
*B
1286064
See ECN
AESA
Change status to final
© Cypress Semiconductor Corporation, 2001-2007. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of
any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for
medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as
critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems
application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Any Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide patent protection (United States and foreign),
United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of,
and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress
integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as specified above is prohibited without
the express written permission of Cypress.
Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein. Cypress does not
assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where
a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems application implies that the manufacturer
assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
Document Number: 38-07138 Rev. *B
Revised June 22, 2007
Page 19 of 19
PSoC Designer™, Programmable System-on-Chip™, and PSoC Express™ are trademarks and PSoC® is a registered trademark of Cypress Semiconductor Corp. All other trademarks or registered
2
trademarks referenced herein are property of the respective corporations. Purchase of I C components from Cypress or one of its sublicensed Associated Companies conveys a license under the
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Philips I C Patent Rights to use these components in an I C system, provided that the system conforms to the I C Standard Specification as defined by Philips. All products and company names
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