PI6C3991
3.3V High-Speed, Low-Voltage
Programmable Skew Clock Buffer
SuperClock
Features
Description
All output pair skew <100ps typical (250 Max.)
3.75 MHz to 80 MHz output operation
User-selectable output functions
Selectable skew to 18ns
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-
mancecomputersystems.Eightindividualdrivers,arrangedasfour
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).
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)
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.
Zero input-to-output delay
50% duty-cycle outputs
LVTTLoutputsdrive50-ohmterminatedlines
Operates from a single 3.3V supply
Low operating current
Divide-by-two and divide-by-four output functions are provided
foradditionalflexibilityindesigningcomplexclocksystems.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.
Availablein32-pinPLCC(J)package
Jitter < 200ps peak-to-peak (< 25ps RMS)
PinConfiguration
LogicBlockDiagram
Test
Phase
Freq.
DET
FB
VCO and
Time Unit
Generator
Filter
REF
4
3
2
1
32 31 30
5
29
28
27
26
25
24
23
22
21
3F1
4F0
4F1
2F0
GND
1F1
1F0
FS
6
4Q0
4Q1
7
4F0
4F1
8
V
CCQ
32-Pin
J
Select Inputs
(three level)
9
V
V
CCN
4Q1
CCN
Skew
3Q0
3Q1
10
11
12
13
1Q0
1Q1
GND
GND
3F0
3F1
4Q0
Select
GND
GND
2Q0
2Q1
2F0
2F1
Matrix
14 15 16 17 18 19 20
1Q0
1Q1
1F0
1F1
PS8450B
04/09/01
1