ETC CY25245

CY25245
Frequency-multiplying, Peak-reducing
EMI Solution
Features
Key Specifications
• Cypress PREMIS™ SMARTSPREAD™ family offering
• Generates an electromagnetic interference (EMI)
optimized clocking signal at the output
• Selectable output frequency range
• Single 1.25%, 2.5%, 5%, or 10% down or center spread
output
• Integrated loop filter components
• Operates with a 3.3 or 5V supply
• Low power CMOS design
• Available in 20-pin Small Shrunk Outline Package
(SSOP)
Supply voltages: .......................................VDD = 3.3V ± 0.3V
or VDD = 5V ± 10%
Frequency range:............................ 13 MHz ≤ Fin ≤ 166 MHz
Cycle-to-cycle jitter: ......................................... 250 ps (max)
Output duty cycle: ................................ 40/60% (worst case)
[1, 2]
Simplified Block Diagram
Pin Configuration
3.3V or 5.0V
SSOP
X1
XTAL
Input
X2
CY25245
Serial Interface
SCLK
OR1^
SCLK
GND
3.3V or 5.0V
OR2*
SSON#^
Oscillator or
Reference Input
1
2
3
4
5
6
7
8
9
10
CY25245
SDATA
Spread Spectrum
Output
(EMI suppressed)
X1
X2
AVDD
MW0^
SDATA
20
19
18
17
16
REFOUT
VDD
GND
IR1*
IR2*
15
SSOUT
14
13
MW1*
GND
12
VDD
11
MW2^
X1
CY25245
SDATA
Serial Interface
Spread Spectrum
Output
(EMI suppressed)
SCLK
Notes:
1. Pins marked with ^ are internal pull-down resistors with weak 250 kΩ.
2. Pins marked with * are internal pull-up resistors with weak 80 kΩ.
Cypress Semiconductor Corporation
Document #: 38-07124 Rev. *A
•
3901 North First Street
•
San Jose, CA 95134
•
408-943-2600
Revised January 7, 2003
CY25245
Pin Definitions
Pin Name Pin No. Pin Type
Pin Description
SSOUT
15
O
Output Modulated Frequency. Frequency modulated copy of the input clock (SSON# asserted).
REFOUT
20
O
Non-modulated Output. This pin provides a copy of the reference frequency. This output will
not have the Spread Spectrum feature enabled regardless of the state of logic input SSON#.
X1
1
I
Crystal Connection or External Reference Frequency Input. This pin has dual functions. It
may either be connected to an external crystal, or to an external reference clock.
X2
2
I
Crystal Connection. Input connection for an external crystal. If using an external reference, this
pin must be left unconnected.
SSON#
10
I
Spread Spectrum Control (Active LOW). Asserting this signal (active LOW) turns the internal
modulation waveform on. This pin has an internal pull-down resistor.
MW0:2
4, 11, 14
I
Modulation Width Selection. When Spread Spectrum feature is turned on, these pins are used
to select the amount of variation and peak EMI reduction that is desired on the output signal.
MW0:Down, MW1:Up, MW2:Down (see Table 2).
IR1:2
17, 16
I
Reference Frequency Selection. The logic level provided at this input indicates to the internal
logic what range the reference frequency is in and determines the factor by which the device
multiplies the input frequency. Refer to Table 3. These pins have internal pull-up resistors.
OR1:2
6, 9
I
Output Frequency Selection Bits. These pins select the frequency operation for the output.
Refer to Table 1. The OR2 pin has an internal pull-up resistor. The OR1 pin has an internal
pull-down resistors.
SCLK
7
I
Clock Pin for SMBus Circuitry.
5
I/O
Data Pin for SMBus Circuitry.
12, 19
P
Power Connection. Connected to 3.3V or 5V power supply.
SData
VDD
AVDD
3
P
Analog Power Connection. Connected to 3.3V or 5V power supply.
GND
8, 13, 18
G
Ground Connection. Connect all ground pins to the common ground plane.
Table 1. Frequency Configuration (Frequencies in MHz)
Range of Fin Frequency
Multiplier
Settings
Output/
Input
Modulation and
Range of Fout Required R Settings Power-down Settings
Min.
Max.
OR2
OR1
Min.
Max.
IR2
IR1
14
41.7
0
1
1
14
41.7
0
1
MW2
Table 2
MW1
14
41.7
1
0
2
28
83.3
0
1
Table 2
14
41.7
1
1
4
56
166
0
1
Table 2
25
83.3
0
1
0.5
13
41.7
1
0
Table 2
25
83.3
1
0
1
25
83.3
1
0
Table 2
25
83.3
1
1
2
50
166
1
0
Table 2
50
166
0
1
0.25
13
41.7
1
1
Table 2
50
166
1
0
0.5
25
83.3
1
1
Table 2
50
166
1
1
1
50
166
1
1
Table 2
Reserved
0
0
N/A
N/A
N/A
As Set
As Set
1
0
Power-down Hi-Z
0
0
N/A
N/A
N/A
As Set
As Set
1
1
Power-down 0
0
0
N/A
N/A
N/A
As Set
As Set
0
0
Power-down 1
0
0
N/A
N/A
N/A
As Set
As Set
0
1
Document #: 38-07124 Rev. *A
Page 2 of 11
CY25245
Table 2. Modulation Width Selection Table
Bandwith Limit Frequencies as a % Value of Fout
EMI Reduction
Modulation Setting
MW0 = 0
MW0 = 1
MW2
MW1
Low
High
Low
High
Minimum EMI Control
0
0
98.75%
100%
99.375%
100.625%
Suggested Setting
0
1
97.5%
100%
98.75%
101.25%
Alternate Setting
1
0
95.0%
100%
97.5%
102.5%
Maximum EMI reduction
1
1
90.0%
100%
95%
105%
Overview
The CY25245 product is one of a series of devices in the
Cypress PREMIS family. The PREMIS family incorporates the
latest advances in PLL spread spectrum frequency synthesizer techniques. By frequency modulating the output with
a low-frequency carrier, peak EMI is greatly reduced. Use of
this technology allows systems to pass increasingly difficult
EMI testing without resorting to costly shielding or redesign.
In a system, not only is EMI reduced in the various clock lines,
but also in all signals which are synchronized to the clock.
Therefore, the benefits of using this technology increase with
the number of address and data lines in the system. The
Simplified Block Diagram shows a simple implementation.
Functional Description
The CY25245 uses a phase-locked loop (PLL) to frequency
modulate an input clock. The result is an output clock whose
frequency is slowly swept over a narrow band near the input
signal. The basic circuit topology is shown in Figure 1. The
input reference signal is divided by Q and fed to the phase
detector. A signal from the VCO is divided by P and fed back
to the phase detector also. The PLL will force the frequency of
the VCO output signal to change until the divided output signal
and the divided reference signal match at the phase detector
input. The output frequency is then equal to the ratio of P/Q
times the reference frequency.[3] The unique feature of the
Spread Spectrum Frequency Timing Generator is that a
modulating waveform is superimposed at the input to the VCO.
This causes the VCO output to be slowly swept across a
predetermined frequency band.
Because the modulating frequency is typically 1000 times
slower than the fundamental clock, the spread spectrum
process has little impact on system performance.
Frequency Selection With SSFTG
In spread spectrum frequency timing generation, EMI
reduction depends on the shape, modulation percentage, and
frequency of the modulating waveform. While the shape and
frequency of the modulating waveform are fixed for a given
frequency, the modulation percentage may be varied.
Using frequency select bits (FS2:1 pins), the frequency range
can be set (see Table 2). Spreading percentage is set with pins
MW0:2 as shown in Table 2.
A larger spreading percentage improves EMI reduction.
However, large spread percentages may either exceed
system maximum frequency ratings or lower the average
frequency to a point where performance is affected. For these
reasons, spreading percentage options are provided.
VDD
Clock Input
Reference Input
Freq.
Divider
Q
Phase
Detector
Σ
Charge
Pump
VCO
Post
Dividers
CLKOUT
(EMI suppressed)
Modulating
Waveform
Feedback
Divider
P
PLL
GND
Figure 1. Functional Block Diagram
Note:
3. For the CY25245, the output frequency is nominally equal to the input frequency.
Document #: 38-07124 Rev. *A
Page 3 of 11
CY25245
Spread Spectrum Frequency Timing Generator
where P is the percentage of deviation and F is the frequency
in MHz where the reduction is measured.
The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occupies. By increasing
the bandwidth of the fundamental and its harmonics, the amplitudes of the radiated electromagnetic emissions are reduced.
This effect is depicted in Figure 2.
The output clock is modulated with a waveform depicted in
Figure 3. This waveform, as discussed in “Spread Spectrum
Clock Generation for the Reduction of Radiated Emissions” by
Bush, Fessler, and Hardin, produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. The
deviation selected for this chip is as described in Table 2.
Figure 3 details the Cypress spreading pattern. Cypress does
offer options with more spread and greater EMI reduction.
Contact your local Sales representative for details on these
devices.
As shown in Figure 2, a harmonic of a modulated clock has a
much lower amplitude than that of an unmodulated signal. The
reduction in amplitude is dependent on the harmonic number
and the frequency deviation or spread. The equation for the
reduction is
dB = 6.5 + 9*log10(P) + 9*log10(F)
Amplitude (dB)
EMI Reduction
Spread
Spectrum
Enabled
NonSpread
Spectrum
Frequency Span (MHz)
Down Spread
Figure 2. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
FREQUENCY
MAX.
MIN.
Figure 3. Typical Modulation Profile
Serial Data Interface
The CY25245 features a two-pin, serial data interface that can
be used to configure internal register settings that control
particular device functions. Upon power-up, the CY25245
initializes with default register settings, therefore the use of this
serial data interface is optional. The serial interface is
write-only (to the clock chip) and is the dedicated function of
device pins SDATA and SCLOCK. In motherboard applications, SDATA and SCLOCK are typically driven by two logic
outputs of the chipset. Clock device register changes are
Document #: 38-07124 Rev. *A
normally made upon system initialization, if any are required.
The interface can also be used during system operation for
power management functions. Table 3 summarizes the control
functions of the serial data interface.
Operation
Data is written to the CY25245 in eleven bytes of eight bits
each. Bytes are written in the order shown in Table 4.
Page 4 of 11
CY25245
Table 3. Serial Data Interface Control Functions Summary
Control Function
Description
Common Application
Clock Output Disable Any individual clock output(s) can be disabled.
Disabled outputs are actively held LOW.
Unused outputs are disabled to reduce EMI and
system power. Examples are clock outputs to unused
PCI slots.
CPU Clock Frequency Provides CPU/PCI frequency selections through For alternate microprocessors and power
Selection
software. Frequency is changed in a smooth and management options. Smooth frequency transition
controlled fashion.
allows CPU frequency change under normal system
operation.
Spread Spectrum
Enabling
Enables or disables spread spectrum clocking.
For EMI reduction.
Output three-state
Puts clock output into a high-impedance state.
Production PCB testing.
(Reserved)
Reserved function for future device revision or
production device testing.
No user application. Register bit must be written as 0.
Table 4. Byte Writing Sequence
Byte
Sequence
Byte Name
Bit Sequence
11010010
Byte Description
1
Slave Address
Commands the CY25245 to accept the bits in Data Bytes 0–6 for internal register
configuration. Since other devices may exist on the same common serial data
bus, it is necessary to have a specific slave address for each potential receiver.
The slave receiver address for the CY25245 is 11010010. Register setting will
not be made if the Slave Address is not correct (or is for an alternate slave
receiver).
2
Command Code Don’t Care
Unused by the CY25245, therefore bit values are ignored (“don’t care”). This byte
must be included in the data write sequence to maintain proper byte allocation.
The Command Code Byte is part of the standard serial communication protocol
and may be used when writing to another addressed slave receiver on the serial
data bus.
3
Byte Count
Don’t Care
Unused by the CY25245, therefore bit values are ignored (“don’t care”). This byte
must be included in the data write sequence to maintain proper byte allocation.
The Byte Count Byte is part of the standard serial communication protocol and may
be used when writing to another addressed slave receiver on the serial data bus.
4
Data Byte 0
5
Data Byte 1
6
Data Byte 2
Refer to Table 5 The data bits in Data Bytes 0–7 set internal CY25245 registers that control device
operation. The data bits are only accepted when the Address Byte bit sequence
is 11010010, as noted above. For description of bit control functions, refer to
Table 5, Data Byte Serial Configuration Map.
7
Data Byte 3
8
Data Byte 4
9
Data Byte 5
10
Data Byte 6
11
Data Byte 7
Writing Data Bytes
Each bit in Data Bytes 0–7 control a particular device function
except for the “reserved” bits which must be written as a logic
0. Bits are written MSB (most significant bit) first, which is bit 7.
Document #: 38-07124 Rev. *A
Table 5 gives the bit formats for registers located in Data Bytes
0–7.
Page 5 of 11
CY25245
Table 5. Data Bytes 0–7 Serial Configuration Map
Affected Pin
Bit(s)
Pin No.
Bit Control
Pin Name
Control Function
0
1
Default
Data Byte 0
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
Data Byte 1
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
7
16
IR2
MSB of Input Range Select
Refer to Table 1
0
6
17
IR1
LSB of Input Range Select
Refer to Table 1
1
5
9
OR2
MSB of Output Range Select
Refer to Table 1
1
4
6
OR1
LSB of Output Range Select
Refer to Table 1
0
3
–
–
Hardware/Software Frequency Select
2
–
–
Stop Function
Data Byte 2
Data Byte 3
Data Byte 4
Document #: 38-07124 Rev. *A
Hardware
Software
0
Normal
Stop
0
Page 6 of 11
CY25245
Table 5. Data Bytes 0–7 Serial Configuration Map (continued)
Affected Pin
Bit Control
Bit(s)
Pin No.
Pin Name
1
10
SSON#
Control Function
0
4
MW0
7
11
6
14
5
20
REFOUT
Output Enable
Disabled
Enabled
1
4
15
SSOUT
Output Enable
Disabled
Enabled
1
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
7
–
–
(Reserved)
–
–
0
6
–
–
(Reserved)
–
–
0
5
–
–
(Reserved)
–
–
0
4
–
–
(Reserved)
–
–
0
3
–
–
(Reserved)
–
–
0
2
–
–
(Reserved)
–
–
0
1
–
–
(Reserved)
–
–
0
0
–
–
(Reserved)
–
–
0
Spread Spectrum
0
1
Default
Spread On
Spread Off
0
LSB of Modulation Width Selection
Refer to Table 2
0
MW2
MSB of Modulation Width Selection
Refer to Table 2
0
MW1
Modulation Width Selection Bit
Refer to Table 2
1
Data Byte 5
Data Byte 6
Data Byte 7
Document #: 38-07124 Rev. *A
Page 7 of 11
CY25245
Absolute Maximum Ratings
Stresses greater than those listed in this table may cause
permanent damage to the device. These represent a stress
rating only. Operation of the device at these or any other condiParameter
tions above those specified in the operating sections of this
specification is not implied. Maximum conditions for extended
periods may affect reliability.
Description
Rating
Unit
VDD, VIN
Voltage on Any Pin with Respect to GND
–0.5 to +7.0
V
TSTG
Storage Temperature
–65 to +150
°C
TA
Operating Temperature
TB
Ambient Temperature under Bias
PD
Power Dissipation
0 to +70
°C
–55 to +125
°C
0.5
W
DC Electrical Characteristics: 0°C < TA < 70°C, VDD = 3.3V ±0.3V[4]
Parameter
Description
IDD
Supply Current
tON
Power Up Time
VIL
Input Low Voltage
VIH
Input High Voltage
VOL
Output Low Voltage
Test Condition
Min.
Typ.
Max.
Unit
18
32
mA
5
ms
0.8
V
0.4
V
50
µA
First locked clock cycle after Power
Good
2.4
V
VOH
Output High Voltage
IIL
Input Low Current
Note 4
–50
2.4
V
IIH
Input High Current
Note 4
–50
IOL
Output Low Current
@ 0.4V, VDD = 3.3V
15
IOH
Output High Current
@ 2.4V, VDD = 3.3V
15
CI
Input Capacitance
RP
Input Pull-Up Resistor
250
kΩ
ZOUT
Clock Output Impedance
25
Ω
µA
50
mA
mA
7
pF
DC Electrical Characteristics: 0°C < TA < 70°C, VDD = 5V ±10%
Parameter
Description
IDD
Supply Current
tON
Power Up Time
VIL
Input Low Voltage
VIH
Input High Voltage
VOL
Output Low Voltage
VOH
Output High Voltage
Test Condition
Min.
Typ.
Max.
Unit
30
50
mA
5
ms
0.15VDD
V
First locked clock cycle after
Power Good
0.7VDD
V
0.4
2.4
V
V
IIL
Input Low Current
Note 4
–50
50
µA
IIH
Input High Current
Note 4
–50
50
µA
IOL
Output Low Current
@ 0.4V, VDD = 5V
24
mA
IOH
Output High Current
@ 2.4V, VDD = 5V
24
mA
CI
Input Capacitance
RP
Input Pull-up Resistor
Clock Output Impedance
ZOUT
Note:
4. Inputs OR1:2 and IR1:2 have a pull-up resistor, Input SSON# has a pull-down resistor.
Document #: 38-07124 Rev. *A
7
pF
250
kΩ
25
Ω
Page 8 of 11
CY25245
AC Electrical Characteristics: TA = 0°C to +70°C, VDD = 3.3V ±0.3V or 5V±10%
Parameter
Description
Test Condition
Min.
Typ.
Max.
Unit
fIN
Input Frequency
Input Clock
14
166
MHz
fOUT
Output Frequency
Spread Off
13
166
MHz
tR
Output Rise Time
15-pF load, 0.8V–2.4V
2
5
ns
tF
Output Fall Time
15-pF load, 2.4V–0.8V
2
5
ns
tOD
Output Duty Cycle
15-pF load
40
60
%
tID
Input Duty Cycle
40
60
%
tJCYC
Jitter, Cycle-to-cycle
300
ps
250
Ordering Information
Ordering Code
Package Type
Product Flow
CY25245PVC
20-pin Plastic SSOP (209-mil)
Commercial, 0°C to 70°C
CY25245PVCT
20-pin Plastic SSOP (209-mil)- Tape and Reel
Layout Example
FB
VDDQ3
µF
0.005 µF
G
C3
G
1
G
20
G
3
V
4
G
5
6
7
8
G
9
10 G
V
CY25245
G
2
G
19
G
18
17
16
G
15
14
G
13
V
12
G
11
G
= 0.005
FB = Vishay
ILB1206
– 300 (300Ω
@C2
100
MHz) µF
or TDK ACB2012L-120 or Murata BLM21B601
µF
Ceramic
Caps
C1 = 10–22
G = VIA to GND plane layer
V =VIA to respective supply plane layer
Note: Each supply plane or strip should have a ferrite bead and capacitors
All bypass caps = 0.1 µF ceramic.
Document #: 38-07124 Rev. *A
Page 9 of 11
CY25245
Package Drawing and Dimension
20-pin (5.3 mm) Shrunk Small Outline Package O20
51-85077-*C
PREMIS and SMARTSPREAD are trademarks of Cypress Semiconductor Corporation. All product and company names
mentioned in this document are the trademarks of their respective holders.
Document #: 38-07124 Rev. *A
Page 10 of 11
© Cypress Semiconductor Corporation, 2003. 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 Semiconductor product. Nor does it convey or imply any license under patent or other rights. Cypress Semiconductor 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
Semiconductor products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress Semiconductor against all charges.
CY25245
Document History Page
Document Title: CY25245 Frequency-multiplying, Peak-reducing EMI Solution
Document Number: 38-07124
Issue
Date
Orig. of
Change
REV.
ECN NO.
**
109865
11/13/01
IKA
New data sheet
*A
122550
01/08/03
RGL
Added SMARTSPREAD in the features area
Document #: 38-07124 Rev. *A
Description of Change
Page 11 of 11