Cypress W152-4, W152-3, W152-2, W152-12, W152-11 Datasheet
...
Spread Aware™, Eight Output Zero Delay Buffer
W152
Cypress Semiconductor Corporation
• 3901 North First Street • San Jose • CA 95134 • 408-943-2600
June 14, 2000, rev . *B
Features
• Spread Aware™—designed to work with SSFTG
reference signals
• T wo banks of four outputs each
• Configuration options to halve, double, or quadruple
the reference frequency refer to
Ta bl e 1
to determine
the specific option which meets your multipl ication
needs
• Outputs may be three-stated
• Available in 16-pin SOIC package
• Extra strength output drive available (-11/-12 versions)
• Contact factory f or availabilit y information on 16-pin
TSSOP
Key Specific ati o n s
Operating Voltage: ............................................... 3.3V±10%
Operating Range: ... .................15 MHz < f
OUTQA
< 140 MHz
Cycle- to - C ycle Jitter: (Re fer to
Figure 3
) ....... .............225 ps
Cycle-to-Cycle Jitter: Frequency Range
25 to140 MHz ........ ........................... .. ............. .. ..... 125 ps
Output to Output Skew: Between Banks.....................215 ps
Output to Output Skew: Within Banks
(Refer to
Figure 4
) .................... ............ ............ ....... 1 0 0 p s
Total Timing Budget Impact:.......... ............................. .555 ps
Max. Phase Error Variation: ......................................±225 ps
Tracking S kew: ........... ............ ............ ............ .. .......... ± 1 3 0 p s
T able 1. Configuration Options
Device Feedback Signal QA0:3 QB0:3
W152-1/11
[1]
QA0:3 or QB0:3 REFx1 REFx1
W152-2/12
[2]
QA0:3 REFx1 REF/2
W152-2/12
[2]
QB0:3 REFx2 REFx1
W152-3 QA0:3 REFx2 REFx1
W152-3 QB0:3 REFx4 REFx2
W152-4 QA0:3 or QB0:3 REFx2 REFx2
Notes:
1. W152-11 has stronger output drive than the W152-1.
2. W152-12 has stronger output drive than the W152-2.
Spread Aware is a trademark of Cypress Semiconducto r Corporation.
Block Diagram
Pin Configuration
QA0
PLL
REF
MUX
QA1
QA2
QA3
QB0
QB1
÷2
SEL0
FBIN
QB2
QB3
SEL1
÷2
(present on the -3 and -4 only)
(present on the -2, -12, and -3 only)
FBIN
QA3
QA2
VDD
GND
QB3
QB2
SEL0
16
15
14
13
12
11
10
9
REF
QA0
QA1
VDD
GND
QB0
QB1
SEL1
1
2
3
4
5
6
7
8
W152
2
Overview
The W152 products are eight-output zero delay buffers. A
Phase-Lock ed Loop (PLL) i s used to tak e a time- varying signal
and provide eight copies of that same signal out. The external
feedback to the PLL provides outputs in phase with the reference inputs.
Internal divid ers exist in some options allo wing the user to get
a simple multiple (/2, x2, x4) of the reference input, for details
see Table 1. Because the outputs are separated into two
banks, it is possi ble to provide some combin ation of these multiples at the sa me time.
Spread Aware
Many syst em s being designed no w utilize a tech nology called
Spread Spectrum F requency Timi ng Generation . Cypress has
been one of the pioneers of SSFTG develop me nt, and we designed this product so as not to filte r off the Spread Spectrum
featur e of the Referen ce input, assuming i t ex ists. When a z ero
delay buffer is not designed to pass the SS feature through,
the result is a significant amount of tracking skew which may
cause problems in systems requiring synch roni zation.
For more details on Spread Spectrum timing technology,
please see the Cypress application note titled, “EMI Suppression Techniques with Spread Spectrum Frequency Timing
Generator (SSFTG) ICs.”
Functional Description
Logic inputs provide the user the ability to turn off one or both
banks of clocks when not in use, as described in Table 2. Disabling a bank of unused outputs will reduce jitter and power
consumption, an d will a ls o reduce th e amount o f EMI gener ated by the W152.
These same inputs al low t he user to by pass the PLL ent irely i f
so desired. When this is done, the device no longer acts as a
zero delay buffer, it simply reverts to a standard eight-output
clock driv er.
The W152 PLL enters an auto power-down mode when there
are no rising edges on the REF inpu t. In this mode, all output s
are three-stated and t he PLL is turned off.
Pin Definitions
Pin Name Pin No.
Pin
Type Pin Description
REF 1 I
Reference Input:
The output signals QA0:3 through QB0:3 will be synchronized to
this signal unless the device is programm ed to bypass the PLL.
FBIN 16 I
Feedback Input:
When programmed to zero delay buffer mode, this input mu st be
fed by o ne of the ou tputs (QA0: 3 or QB 0:3) to e nsur e proper f unctio nality. If t he tr ace
between FBIN and the output pin being used for fe edback is equal in length to the
traces betwe en the outputs and the signal destinations, t hen the signals received at
the destinations will be synchronized to the REF signal input.
QA0:3 2, 3, 14, 15 O
Outputs from Bank A:
The frequency of the signals provided by these pins is determined by the f eedbac k signal connected to FBIN, and the sp ecific W152 op tion being
used. See Table 2.
QB0:3 6, 7, 10, 11 O
Outputs from Bank B:
The frequency of the signals provided by these pins is determined by the f eedbac k signal connected to FBIN, and the sp ecific W152 op tion being
used. See Table 2.
VDD 4, 13 P
Power Connections:
Connect to 3.3V. Use ferrite beads to help reduce noise for
optimal jitter performance.
GND 5, 12 G
Ground Connections:
Connect all grounds to the common system ground plane.
SEL0:1 9, 8 I
Function Select Inputs:
Tie to V
DD
(HIGH, 1) or GND (LOW, 0) as desired per
T able 2.
T able 2. Input Logic
SEL1 SEL0 QA0:3 QB0:3 PLL
0 0 Three-State Three-State Shutdown
0 1 Active Three-State Active, Utilized
1 0 Active Active Shutdown,
Bypassed
1 1 Active Active Active, Utilized
W152
3
How to Implement Zero Delay
Typically, zero delay buffers (ZDBs) are used because a designer wants to provide multiple copies of a clock signal in
phase with each other . The whole c oncept behin d ZDBs is that
the signals at the destination chips are all going HIGH at the
same time as the input to the ZDB. In order to achieve this,
layou t must com pensate f or tra ce length be tween the ZDB an d
the target devices. The method of compensation is described
below.
External feedbac k is the trait that allows f or thi s compensati on.
The PLL on the ZDB will cause the feedback signal to be in
phase with the reference signal. When laying out the board,
match the trace lengths between the output being used for
feedback and the FBIN input to the PLL.
If it is desirable to either add a little delay, or slightly precede
the input signal, this m ay also be affec ted by either making the
trace to the FBIN pin a little shorter or a little longer than the
traces to the devices being clocked.
Inserti n g Other Devices in Feedback Path
Another nice feature available due to the external feedback is
the ability to synchronize signals up to the signal coming from
some other dev ic e. Thi s impl ement ation can be appl ied t o an y
device (ASIC, mult iple output cloc k buffer /driver, etc.) which is
put into the feedback path.
Referring to Figure 2 , if the traces between the ASIC/buffer
and the destination of the clock signa l(s) (A) are equal in lengt h
to the trace between the buffer and the FBIN pin, the signals
at the destination(s) device will be driven HIGH at the same
time the Reference clock provided to the ZDB goes HIGH.
Synchronizing the other out puts of t he ZDB to the outputs f orm
the ASIC/Buff er is mor e comp le x ho we v er, as any propaga tion
delay in the ASIC/Buf fer must be accounted for.
9
2
3
1
4
7
6
8
5
16
13
14
15
10
11
12
3.3V
Supply
VDD
0.1 µF
0.1 µF
10 µF
Ferrite
Bead
See Note 3
VDD or GND (for desired operation mode)
VDD or GND (for desired operation mode)
QA0
QA2QA1
QA3
Ground
PowerPower
FB InRef In
QB1
QB0
QB2
QB3
SEL1 SEL0
Ground
VDD
Figure 1. Schematic
[3]
Note:
3. Pin 16 needs to be connected to one of the outputs from either bank A or bank B, it should not be connected to both. Pins 2 and 10 are shown here as
examples. None of the outputs should be considered aas preferred for the feedback path.
Reference
Signal
Feedback
Input
ASIC/
Buffer
Zero
Delay
Buffer
A
Figure 2. 6 Output Buffer in the Feedback Path
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