PI6C3421A
27MHz Spread Spectrum
Clock Synthesizer
Product Features
• 14.318 MHz input frequency, (crystal or external reference)
• Two High Precision outputs:
—27.000 MHz SSC clock output
—27.000 MHz clock output
• Four Down-Spread options:
— Down-spread: -0.25%, -0.5%, -0.75% and -1.0% typical at
14.318MHz input
• Single 3.3V Power Supply
• Modulation Rate: Fin /448
• Industrial and commercial temperature supported
• Packaging ( Pb-Free and Green):
— SOTiny™ 6-pin SOT-23 (T)
Applications
The PI6C3421A can be used in most multimedia applica-
tions and embedded systems including but not limited to the
following:
•
PDAs
•
DSCs
•
Printers/ MFPs
•
Media players
•
Portable-TVs
•
Embedded digital video devices
•
CD-ROM, VCD and DVD players
•
LCD Panel Modules
•
Automotive components
•
Networking devices
Benefits
•
Reduction in EMI
•
System cost saving
•
Reduced system complexity
•
Faster time to market
Description
The PI6C3421A is a Spread Spectrum Clock Synthesizer and
part of the Pericom SSCG product family. The part generates
one high precision 27.000 MHz spread spectrum clock
output from a single clock source or a crystal and one 27.000
MHz un-modulated clock output, and is designed to reduce
electromagnetic interference (EMI) by spreading the clock.
This reduction in EMI can result in significant system cost
saving and less design complexity by reducing the number of
circuit board layers ferrite beads and shielding. In the absence
of a spread spectrum clock, other EMI-reducing components
are required in order to comply with regulatory agency
requirements.
The spreading ratio is selectable using the selection pins. The
PI6C3421A provides -0.25%, -0.5%, -0.75% and -1.0% spread
modulation through external logic stage setting. The variety and
the reduced size of the package outlines can save precious board
space and make layout easier.
PI6C3421A is one of the clock products provided by Pericom.
If your application needs a clock product with a different
specification not currently provided, please contact us for
further information or custom design.
Block Diagram
Pin Configuration
REFIN/X1
X2
S0
S1
27M
Clock
Synthesizer
27M_SSC
X1/REFIN
GND
27M_SSC/S0
6-Pin
SOT-23
X2/S1
V
DD
27M
07-0120
1
PS8836E
05/22/07
PI6C3421A
27MHz Spread Spectrum
Clock Synthesizer
Pin Description
Pin Name
X1/REFIN
GND
27M_SSC/S0
Pin No
1
2
3
I/O Type
I
Ground
I/O
Description
Crystal or reference clock input
Ground
27M_SSC/SO is a multi-functional pin. S0 is active during power
on for spreading ratio selection then switches to 27MHz SSC clock
output.
27MHz clock output.
Power Supply
X2/S1 is a multiple function pin. S1 is active during power on
selection of SSC spread then switches to crystal input.
27M
V
DD
X2/S1
4
5
6
O
Power
I/O
Spread Ration Configuration
(V
DD
= 3.3V± 10%, Ambient Temperature = 25˚C, f
OUT
= 27 MHz)
S0
0
0
1
1
S1
0
1
0
1
Down - Spread(%)
-0.25
-0.5
-0.75
-1.0
07-0120
2
PS8836E
05/22/07
PI6C3421A
27MHz Spread Spectrum
Clock Synthesizer
Electrical Specifications
Maximum Ratings
(1)
Supply Voltage to Ground ....................................................................... 5.5V
All Inputs and Outputs ..................................................... -0.5V to V
DD
+0.5V
Storage Temperature .............................................................-65°C to +150°C
Operating Temperature ............................................................... -40 to +85°C
Junction Temperature ............................................................................150°C
Soldering Temperature ..........................................................................260°C
Note:
1. Stresses greater than those listed under MAXIMUM
RATINGS may cause permanent damage to the device.
This is a stress rating only and functional operation of the
device at these or any other conditions above those indi-
cated in the operational sections of this specification is not
implied. Exposure to absolute maximum rating conditions
for extended periods may affect reliability.
DC Characteristics
(V
DD
= 3.3V ±10%, Ambient Temperature -40°C to +85
o
C, f
IN
= 14.318 MHz)
Symbol
V
DD
V
IH
V
IL
V
OH
V
OH
V
OL
V
OL
I
DD
Z
OUT_UP
C
IN
Parameter
Operating Voltage
Input High Voltage
Input Low Voltage
Output High Voltage
Output High Voltage
Output Low Voltage
Output Low Voltage
Supply Current
Nominal Output Impedance
Input Capacitance
Conditions
Min.
+3.0
2
2.4
2.0
0.4
0.6
55
65
40
6
Typ.
(1)
+3.3
Max.
+3.6
0.8
I
OH
= -4 mA
I
OH
= -6 mA
I
OL
= 4 mA
I
OL
= 6 mA
All outputs active with C
L =
15pF load
High side buffer
Input pins
Unit
V
V
V
V
V
V
V
mA
Ω
Ω
pF
Z
OUT_LOW
Nominal Output Impedance Low side buffer
AC Characteristics
(V
DD
= 3.3V ±10%, Ambient Temperature –40°C to +85
o
C)
Parameter
Conditions
REFIN Input Frequency
REFIN Clock Input
Clock Output Frequency
Multiplication factor (f
IN
/f
OUT
= 1.885715)
Output Clock Rise Time
From 0.4V to 2.4V, CL = 15pF load
Output Clock Fall Time
From 2.4V to 0.4V, CL = 15pF load
TJ_SHORT
Short term jitter
Cycle-to-cycle jitter (f
OUT
= 27 MHz)
Input Clock Duty Cycle REFIN/X1, Measured @ V
DD
/2 (f
OUT
= 27 MHz)
T
IDC
Output Clock Duty
Measured @ V
DD
/2 (f
OUT
= 27 MHz)
T
ODC
Cycle
∆
ƒ/ƒ
Actual mean frequency
Input frequency = 14.31818 MHz, Output fre-
error versus target
quency = 27 MHz
Note:
1. Typical conditions are at 3.3V for room temperature at 25°C
Symbol
f
IN
f
OUT
tRISE
tFALL
Min.
8
15.1
20
45
Typ.
(1)
14.318
27
3
2.7
250
50
50
0
Max.
24.5
46.2
350
80
55
Unit
MHz
MHz
ns
ns
ps
%
%
ppm
07-0120
3
PS8836E
05/22/07
PI6C3421A
27MHz Spread Spectrum
Clock Synthesizer
Application Information
Decoupling Capacitor
Two decoupling capacitors of 0.1uF and 1nF must be connected in parallel between VDD and GND. To optimize device performance
and to lower output noise, the coupling capacitors should be placed on the component side of the board as close to these pins as
possible. There should be no vias placed between the decoupling capacitors and VDD pin. The PCB trace to VDD pin should be as
short as possible, and no vias should be placed between VDD and the capacitors in the decoupling circuit. 10kΩ to 50kΩ pull-up or
pull-down resistors, depending on the application, should be used on S0 and S1 to select the logical state and corresponding spread-
ing ratio.
VDD
0.1uF 1nF
0.1uF 1nF
VDD
VDD
S0/
S1
Connect to low
S0/
S1
Connect to high
1. PI6C3421A can accept a 14.31818 MHz reference clock or crystal clock.
2. Power supply pin decoupling capacitors should be placed as close as possible to VDD pin. Via's at the VDD pin should be avoided.
3. Spread select pin's (S0 and S1):
Pin 3 (27M_SSC/S0) and Pin 6 (X2/S1) provide logic state strapping function. When strapping resistor connects to VDD, S0 and S1 are
set to logic HIGH. When strapping resistor connects to Ground, S0 or S1 will set to logic LOW.
4. Refer to "Spread Spectrum Selection Table", for more details on the strapping logic.
Crystal Load Capacitors
If a crystal is used with the device, the external trim capacitors C
Ltrim
are used to adjust the effective capacitance to match the
required crystal load capacitance. The C
Ltrim
value can be derived from formula C
Ltrim
= 2*C
L
– (Cs + Ci). Typical C
Ltrim
= 28pF
when crystal load = 18pF, stray capacitance C
s
= 3pF and XTAL pins capacitance = 5pF.
Xtal
X1
C
Ltrim
X2
C
Ltrim
Series Termination Resistor
For optimal performance, a series termination resistor should be used, when the PCB trace between the clock output and the load
is over 1 inch. A 10Ω resistor should be used to series terminate a 50Ω trace, a typical trace impedance found on PCB boards. The
series termination resistor should be placed in series and as close to the clock output as possible. The nominal impedance measured
at the clock output of the part is 40Ω.
PCB Layout Recommendation
To optimize device performance, all components should be placed on the same side of the board and, therefore, no vias are used
through other signal layers. The part should be kept away from other signal traces including ones just underneath the part or on
layers adjacent to the ground plane layer used by the part. The PCB trace from the part to the ground via should be kept as short as
possible
07-0120
4
PS8836E
05/22/07
PI6C3421A
27MHz Spread Spectrum
Clock Synthesizer
Recommended Crystal Specification
Pericom recommends SRX7316-E Crystal for optimum performance.
Parameter
Value
Mode of oscillation, and cut
Fundamental AT
Frequency
14.318
Frequency Tolerance
±20
Temperature
±30
Load Cap
18
Equivalent series resistance
40
Drive to level
100
Aging Stability
±5
Size (Length x Width x Height)
11.18(.440) x 4.65(.83) x 13.46(.53)
Units
MHz
PPM
PPM
pF
Ω
μW
PPM/YR
mm(inch)
07-0120
5
PS8836E
05/22/07
