FB
REF
Phase
Freq.
DET
FS
4F0
4F1
Filter
VCO and
Time Unit
Generator
4Q0
Select Inputs
(three level)
4Q1
Skew
Select
Matrix
3Q0
3Q1
2Q0
2Q1
1Q0
1Q1
3F1
4F0
4F1
V
CCQ
V
CCN
4Q1
4Q0
GND
GND
3F0
FS
V
CCQ
REF
GND
TEST
2F1
4
5
6
7
8
9
10
11
12
13
14 15 16 17 18 19
20
3
2
1
32 31
30
29
28
27
V
CCN
FB
V
CCN
3Q1
3Q0
1F0
1F1
1
2Q1
2Q0
21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
PI6C3991
3.3V High-Speed, Low-Voltage
Programmable Skew Clock Buffer
SuperClock
®
Features
• All output pair skew <100ps typical (250 Max.)
• 3.75 MHz to 80 MHz output operation
• User-selectable output functions
— Selectable skew to 18ns
— Inverted and Non-Inverted
— Operation at ½ and ¼ input frequency
— Operation at 2X and 4X input frequency
(input as low as 3.75 MHz, x4 operation)
• Zero input-to-output delay
• 50% duty-cycle outputs
• LVTTL outputs drive 50-ohm terminated lines
• Operates from a single 3.3V supply
• Low operating current
• Available in 32-pin PLCC (J) package
• Jitter < 200ps peak-to-peak (< 25ps RMS)
Description
PI6C3991 offers 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. Eight individual drivers, arranged as four
pairs of user-controllable outputs, can each drive terminated trans-
mission lines with impedances as low as 50 ohms while delivering
minimal and specified output skews and full-swing logic levels
(LVTTL).
Each output can be hardwired to one of nine skews or function
configurations. Delay increments of 0.7ns to 1.5ns are determined
by the operating frequency with outputs able to skew up to ±6 time
units from their nominal “zero” skew position. The completely
integrated PLL allows external load and transmission line delay
effects to be canceled. The user can create output-to-output skew
up to ±12 time units.
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 allow
distribution of a low-frequency clock that can be multiplied by
two or four at the clock destination. This feature allows flexibility
and simplifies system timing distribution design for complex
high-speed systems.
Logic Block Diagram
Test
Pin Configuration
3F0
3F1
2F0
2F1
32-Pin
J
26
25
24
23
22
21
2F0
GND
1F1
1F0
V
CCN
1Q0
1Q1
GND
GND
PS8450D
03/06/08
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21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
PI6C3991
3.3V High-Speed, Low-Voltage Programmable
Skew Clock Buffer
- SuperClock
®
Pin Descriptions
Signal Name
REF
FB
FS
1F0, 1F1
2F 0, 2F 1
3F 0, 3F 1
4F 0, 4F 1
TEST
1Q0, 1Q1
2Q 0, 2Q 1
3Q 0, 3Q 1
4Q 0, 4Q 1
V
CCN
V
CCQ
GND
I/O
I
I
I
I
I
I
I
I
O
O
O
O
PWR
PWR
De s cription
Reference frequency input. This input supplies the frequency and timing against which all functional variation is measured.
PLL feedback input (typically connected to one of the eight outputs)
Three- level frequency range select. see Table 1.
Three- level function select inputs for output pair 1 (1Q0, 1Q1). See Table 2.
Three- level function select inputs for output pair 2 (2Q0, 2Q1). See Table 2.
Three- level function select inputs for output pair 3 (3Q0, 3Q1). See Table 2.
Three- level function select inputs for output pair 4 (4Q0, 4Q1). See Table 2.
Three- level select. See test mode section under the block diagram descriptions
Output pair 1. See Table 2
Output pair 2. See Table 2
Output pair 3. See Table 2
Output pair 4. See Table 2
Power supply for output drivers
Power supply for internal circuitry
PWR Ground
Table 1. Frequency Range Select and t
U
Calculation
(1)
Table 2. Programmable Skew Configurations
(1)
FS
(1,2)
LOW
MID
HIGH
F
NOM
(M Hz)
M in.
15
25
40
M a x.
30
50
80
t
U
=
1
f
NOM
× N
whe re N=
44
26
16
Approximate
Fre q. (M Hz) at
which t
U
= 1.0ns
22.7
38.5
62.5
Function Se le cts
1F1, 2F1,
3F1, 4F1
LOW
LOW
LOW
MID
MID
MID
HIGH
HIGH
HIGH
1F0, 2F0,
3F0, 4F0
LOW
MID
HIGH
LOW
MID
HIGH
LOW
MID
HIGH
1Q0, 1Q1,
2Q0, 2Q1
–4t
U
–3t
U
–2t
U
–1t
U
0t
U
+1t
U
+2t
U
+3t
U
+4t
U
Output Functions
3Q0, 3Q1
Divide by 2
–6t
U
–4t
U
–2t
U
0t
U
+2t
U
+4t
U
+6t
U
Divide by 4
4Q0, 4Q1
Divide by 2
–6t
U
–4t
U
–2t
U
0t
U
+2t
U
+4t
U
+6t
U
Inverted
Notes:
1. For all three-state inputs, HIGH indicates a connection to V
CC
, LOW indicates a connection to GND, and MID indicates an
open connection. Internal termination circuitry holds an unconnected input to V
CC
/2.
2. The level to be set on FS is determined by the “normal” operating frequency (f
NOM
) and Time Unit Generator
(see Logic Block Diagram). Nominal frequency (f
NOM
) 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 will be f
NOM
when the output connected
to FB is undivided. The frequency of the REF and FB inputs will be f
NOM
/2 or f
NOM
/4 when the part is configured for a frequency
multiplication by using a divided output as the FB input.
2
PS8450D
11/12/08
Block Diagram Description
Phase Frequency Detector and Filter
These two blocks accept input signals 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.
VCO and Time Unit Generator
The VCO accepts analog control inputs from the PLL filter block
and generates a frequency that is used by the time unit generator
to create discrete time units that are selected in the skew mix matrix.
The operational range of the VCO is determined by the FS control
pin. The time unit (t
U
) is determined by the operating frequency of
the device and the level of the FS pin as shown in Table 1.
Skew Select Matrix
The skew select matrix is comprised of four independent sections.
Each section has two low-skew, high-fanout drivers (xQ0, xQ1),
and two corresponding three-level function select (xF0, xF1)
inputs. Table 2 shows the nine possible output functions for each
section as determined by the function select inputs. All times are
measured with respect to the REF input assuming that the output
connected to the FB input has 0t
U
selected.
t
0
+1t
U
t
0
+2t
U
t
0
+3t
U
t
0
+4t
U
t
0
+5t
U
t
0
+6t
U
t
0
–6t
U
t
0
–5t
U
t
0
–4t
U
t
0
–3t
U
t
0
–2t
U
t
0
–1t
U
t
0
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21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
PI6C3991
3.3V High-Speed, Low-Voltage Programmable
Skew Clock Buffer
- SuperClock
®
Test Mode
The TEST input is a three-level input. In normal system operation,
this pin is connected to ground, allowing the PI6C3991 to operate
as explained briefly above (for testing purposes, any of the three
level inputs can have a removable jumper to ground, or be tied LOW
through a 100 Ohm resistor. This will allow an external tester to
change the state of these pins.)
If the TEST input is forced to its MID or HIGH state, the device will
operate with its internal phase locked loop disconnected, and input
levels supplied to REF will directly control all outputs. Relative
output to output functions are the same as in normal mode.
In contrast with normal operation (TEST tied LOW). All outputs
will function based only on the connection of their own function
select inputs (xF0 and xF1) and the waveform characteristics of
the REF input.
Maximum Ratings
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) ............................... 64mA
Static Discharge Voltage ............................................... >2001V
(per MIL-STD-883, Method 3015)
Latch-Up Current .........................................................>200mA
1Fx
2Fx
(N/A)
LL
LM
LH
ML
MM
MH
HL
HM
HH
FB Input
REF Input
3Fx
4Fx
LM
–6t
U
LH
(N/A)
ML
(N/A)
MM
(N/A)
MH
(N/A)
HL
–4t
U
–3t
U
–2t
U
–1t
U
0t
U
+1t
U
+2t
U
+3t
U
+4t
U
Operating Range
Range
Commercial
Industrial
Ambie nt Te mpe rature
0°C to +70°C
–40°C to +85°C
V
CC
3.3V ±10%
3 . 3 V ± 10 %
Note:
3. FB connected to an output selected for "zero" skew
(ie., xF1 = xF0 = MID).
(N/A) HM
+6t
U
(N/A) LL/HH Divided
(N/A)
HH Invert
Figure 1. Typical Outputs with FB Connected to a
Zero-Skew Output
(3)
3
PS8450D
11/12/08
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21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
PI6C3991
3.3V High-Speed, Low-Voltage Programmable
Skew Clock Buffer
- SuperClock
®
Capacitance
(6)
Parame te r
C
IN
De s cription
Input Capacitance
Te s t Conditions
T
A
= 25°C, f = 1MHz, V
CC
= 3.3V
M ax.
10
Units
pF
Electrical Characteristics
(Over the Operating Range)
Parame te r
V
OH
V
OL
V
IH
V
IL
V
IHH
V
IMM
V
ILL
I
IH
I
IL
I
IHH
I
IMM
I
ILL
I
OS
I
CCQ
I
CCN
De s cription
Output HIGH Voltage
Output LOW Voltage
Input HIGH Voltage (REF & FB
inputs only)
Input LOW Voltage (REF & FB inputs
only)
Three- Level Input HIGH Voltage
(Test, FS, xFn)
(4)
Three- Level Input MID Voltage
(Test, FS, xFn)
(4)
Three- Level Input LOW Voltage
(Test, FS, xFn)
(4)
Input HIGH Leakage Current
(REF & FB inputs only)
Input LOW Leakage Current
(REF & FB inputs only)
Input HIGH Current (Test, FS, xFn)
Input MID Current (Test, FS, xFn)
Input LOW Current (Test, FS, xFn)
Short Circuit Current
(5)
Operating Current Used by Internal
Circuitry
Output Buffer Current per Output Pair
Min.
≤
V
CC
≤
Max.
Min.
≤
V
CC
≤
Max.
Min.
≤
V
CC
≤
Max.
V
CC
= Max., V
IN
= Max.
V
CC
= Max., V
IN
= 0.4V
V
IN
= V
CC
V
IN
= V
CC
/2
V
IN =
GND
V
CC
= Max., V
OUT
= GND (25°C only)
V
CCN
= V
CCQ
= Max.,
All Input Selects Open
V
CCN
= V
CCQ
= Max.,
I
OUT
= 0mA
All Input Selects Open, f
MAX
V
CCN
= V
CCQ
= Max.,
I
OUT
= 0mA
All Input Selects Open, f
MAX
Com'l
Mil/Ind
–50
–200
–200
95
100
19
mA
mA
mA
–20
200
50
Te s t Conditions
V
CC
= Min., I
OH
= –12mA
V
CC
= Min., I
OL
= 35mA
2.0
–0.5
0.87 V
CC
0.47 V
CC
0.0
M in.
2.4
0.45
V
CC
0.8
V
V
CC
0.53 V
CC
0.13 V
CC
20
M a x.
Units
μ
A
PD
Power Dissipation per Output Pair
104
mW
Notes:
4. These inputs are normally wired to V
CC
, GND, or left unconnected (actual threshold voltages vary as a percentage of V
CC
). Internal
termination resistors hold unconnected inputs at V
CC
/2. If these inputs are switched, the function and timing of the outputs may glitch
and the PLL may require an additional t
LOCK
time before all data sheet limits are achieved.
5. PI6C3991 should be tested one output at a time, output shorted for less than one second, less than 10% duty cycle.
Room temperature only.
6. Applies to REF and FB inputs only. Tested initially and after any design or process changes that may affect these parameters.
4
PS8450D
11/12/08
21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
21098765432121098765432109876543210987654321210987654321098765432109876543212109876543210987654321098765432121098765432109876543210987654321
PI6C3991
3.3V High-Speed, Low-Voltage Programmable
Skew Clock Buffer
- SuperClock
®
Switching Characteristics PI6C3991
(Over the Operating Range)
(2,7)
Parame te r
Operating
Clock Frequency
in MHz
REF Pulse Width HIGH
REF Pulse Width LOW
Programmable Skew Unit
Zero Output Matched- Pair Skew (XQ0, XQ1)
(9,10)
Zero Output Skew (All Outputs)
(9,11)
Output Skew (Rise- Rise, Fall- Fall, Same Class Outputs)
(9,13)
Output Skew (Rise- Fall, Nominal- Inverted, Divided- Divided)
(9,13)
Output Skew (Rise- Rise, Fall- Fall, Different Class Outputs)
(9,13)
Output Skew (Rise- Fall, Nominal- Divided, Divided- Inverted
Device- to- Device Dkew
(8,14)
(9,13)
De s cription
FS = LOW
(1,2)
FS = MID
(1,2)
FS = HIGH
(1,2)
PI6C3991-2
M in.
15
25
40
5.0
5.0
See Table 1
0.05
0.1
0.1
0.5
0.25
0.5
–0.25
–0.65
0.0
0.0
0.2
0.25
0.5
1.0
0.5
0.9
1. 2 5
+0.25
+0.65
2.0
1.5
0.15
0.15
1.0
1.0
1.2
1.2
0.5
25
200
Typ.
M a x.
30
50
80
PI6C3991-5
M in.
15
25
40
5.0
5.0
See Table 1
0.1
0.25
0.6
0.5
0.5
0.5
–0.5
–1.0
0.0
0.0
0.25
0.5
0.7
1.0
0.7
1.0
1.25
+0.5
+1.0
2.5
3.0
0.15
0.15
1.0
1.0
1.5
1.5
0.5
25
200
0.15
0.15
–0.7
–1.2
Typ. M ax.
30
50
80
M in.
15
25
40
5.0
5.0
PI6C3991
Typ.
M ax. Units
30
50
80
ns
See Table 1
0.1
0.3
0.6
1.0
0.7
1.2
0.0
0.0
0.25
0.75
1. 0
1.5
1.2
1.7
1.65
+0.7
+1.2
3
3.5
1.5
1.5
2.5
2.5
0.5
25
200
ms
ps
ns
MHz
f
NOM
t
RPWH
t
RPWL
t
U
t
SKEWPR
t
SKEW0
t
SKEW1
t
SKEW2
t
SKEW3
t
SKEW4
t
DEV
t
PD
t
ODCV
t
PWH
t
PWL
t
ORISE
t
OFALL
t
LOCK
t
JR
Propagation Delay, REF Rise to FB Rise
Output Duty Cycle Variation
(15)
Output HIGH Time Deviation from 50%
(16)
Output LOW Time Deviation from 50%
(16)
Output Rise Time
(16,17)
Output Fall Time
(16,17)
PLL Lock Time
(18)
Cycle- to- cycle
Output Jitter
RMS
(8)
Peak- to- peak
(8)
Notes:
7. Test measurement levels for the PI6C3991 are TTL levels (1.5V to 1.5V). Test conditions assume signal transition times of 2ns or less
and output loading as shown in the AC Test Loads and Waveforms unless otherwise specified.
8. Guaranteed by statistical correlation. Tested initially and after any design or process changes that may affect these parameters.
9. SKEW is defined as the time between the earliest and the latest output transition among all outputs for which the same t
U
delay has
been selected when all are loaded with 30pF and terminated with 50 Ohm to V
CC
/2.
10. t
SKEWPR
is defined as the skew between a pair of outputs (XQ0 and XQ1) when all eight outputs are selected for 0t
U
.
11. t
SKEW0
is defined as the skew between outputs when they are selected for 0t
U
. Other outputs are divided or inverted but not shifted.
12. C
L
= 0pF. For C
L
= 30pF, t
SKEW0
= 0.35ns.
13. There are three classes of outputs: Nominal (multiple of t
U
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).
14. t
DEV
is the output-to-output skew between any two devices operating under the same conditions (V
CC
ambient temperature, air flow,
etc.)
15. t
ODCV
is the deviation of the output from a 50% duty cycle. Output pulse width variations are included in t
SKEW2
and t
SKEW4
specifications.
16. Specified with outputs loaded with 30pF for the PI6C3991 and PI6C3991-5 devices. Devices are terminated through 50 Ohm to V
CC
/
2. t
PWH
is measured at 2.0V. t
PWL
is measured at 0.8V.
17. t
ORISE
and t
OFALL
measured between 0.8V and 2.0V.
18. t
LOCK
is the time that is required before synchronization is achieved. This specification is valid only after V
CC
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 t
PD
is within
specified limits.
5
PS8450D
11/12/08
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