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DATASHEET
FIELD PROGRAMMABLE SS VERSACLOCK SYNTHESIZER Description
The ICS251 is a low cost, single-output, field programmable clock synthesizer. The ICS251 can generate an output frequency from 314 kHz to 200 MHz and may employ Spread Spectrum techniques to reduce system electro-magnetic interference (EMI). Using ICS' VersaClockTM software to configure the PLL and output, the ICS251 contains a One-Time Programmable (OTP) ROM to allow field programmability. Programming features include 4 selectable configuration registers. The device employs Phase-Locked Loop (PLL) techniques to run from a standard fundamental mode, inexpensive crystal, or clock. It can replace multiple crystals and oscillators, saving board space and cost. The device also has a power-down feature that tri-states the clock outputs and turns off the PLLs when the PDTS pin is taken low. The ICS251 is also available in factory programmed custom versions for high-volume applications.
ICS251
Features
* * * * * * * * * * *
8-pin SOIC package Four addressable registers Input crystal frequency of 5 to 27 MHz Clock input frequency of 3 to 150 MHz Output clock frequencies up to 200 MHz Configurable Spread Spectrum Modulation Operating voltage of 3.3 V Replaces multiple crystals and oscillators Controllable output drive levels Advanced, low-power CMOS process Available in RoHS compliant packaging
Block Diagram
VDD
S1:0
Crystal or clock input X1/ICLK
2
OTP ROM with PLL Divider Values
PLL Clock Synthesis, Spred Spectrum and Control Circuitry
CLK
Crystal Oscillator X2 External capacitors are required with a crystal input.
GND PDTS (output and PLL)
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Pin Assignment
S0 VDD X1/ICLK X2 1 2 3 4 8 7 6 5 PDTS GND S1 CLK
Output Clock Selection Table
S1
0 0 1 1
S0
0 1 0 1
CLK (MHz)
User Configurable User Configurable User Configurable User Configurable
Spread Percentage
User Configurable User Configurable User Configurable User Configurable
8-pin (150 mil) SOIC
Pin Descriptions
Pin Number
1 2 3 4 5 6 7 8
Pin Name
S0 VDD X1/ICLK X2 CLK S1 GND PDTS
Pin Type
Input Power XI XO Output Input Power Input Connect to +3.3 V.
Pin Description
Select pin 0 for frequency selection on CLK. Internal pull-up resistor. Connect this pin to a crystal or external clock input. Connect this pin to a crystal, or float for clock input. Clock output. Weak internal pull-down when tri-state. Select pin 1 for frequency selection on CLK. Internal pull-up resistor. Connect this to Ground. Powers down entire chip. Tri-states CLK outputs when low. Internal pull-up resistor.
External Components
The ICS251 requires a minimum number of external components for proper operation. small capacitors from X1 to ground and from X2 to ground. These capacitors are used to adjust the stray capacitance of the board to match the nominally required crystal load capacitance. Because load capacitance can only be increased in this trimming process, it is important to keep stray capacitance to a minimum by using very short PCB traces (and no vias) been the crystal and device. Crystal capacitors must be connected from each of the pins X1 and X2 to ground. The value (in pF) of these crystal caps should equal (CL -6 pF)*2. In this equation, CL= crystal load capacitance in pF. Example: For a crystal with a 16 pF load capacitance, each crystal capacitor would be 20 pF [(16-6) x 2] = 20.
Series Termination Resistor
Clock output traces over one inch should use series termination. To series terminate a 50 trace (a commonly used trace impedance), place a 33 resistor in series with the clock line, as close to the clock output pin as possible. The nominal impedance of the clock output is 20.
Decoupling Capacitor
As with any high-performance mixed-signal IC, the ICS251 must be isolated from system power supply noise to perform optimally. A decoupling capacitor of 0.01F must be connected between VDD and the PCB ground plane.
PCB Layout Recommendations
For optimum device performance and lowest output phase noise, the following guidelines should be observed. 1) The 0.01F decoupling capacitor should be mounted on
Crystal Load Capacitors
The device crystal connections should include pads for
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the component side of the board as close to the VDD pin as possible. No vias should be used between the decoupling capacitor and VDD pin. The PCB trace to VDD pin should be kept as short as possible, as should the PCB trace to the ground via. Distance of the ferrite bead and bulk decoupling from the device is less critical. 2) The external crystal should be mounted just next to the device with short traces. The X1 and X2 traces should not be routed next to each other with minimum spaces, instead they should be separated and away from other traces. 3) To minimize EMI, the 33 series termination resistor (if needed) should be placed close to the clock output. 4) An optimum layout is one with all components on the same side of the board, minimizing vias through other signal layers. Other signal traces should be routed away from the ICS251. This includes signal traces just underneath the device, or on layers adjacent to the ground plane layer used by the device.
fall times for each drive option.)
ICS VersaClock Software
ICS applies years of PLL optimization experience into a user friendly software that accepts the user's target reference clock and output frequencies and generates the lowest jitter, lowest power configuration, with only a press of a button. The user does not need to have prior PLL experience or determine the optimal VCO frequency to support multiple output frequencies. VersaClock software quickly evaluates accessible VCO frequencies with available output divide values and provides an easy to understand, bar code rating for the target output frequencies. The user may evaluate output accuracy, performance trade-off scenarios in seconds.
Spread Spectrum Modulation
The ICS251 utilizes frequency modulation (FM) to distribute energy over a range of frequencies. By modulating the output clock frequencies, the device effectively lowers energy across a broader range of frequencies; thus, lowering a system's electro-magnetic interference (EMI). The modulation rate is the time from transitioning from a minimum frequency to a maximum frequency and then back to the minimum. Spread Spectrum Modulation can be applied as either "center spread" or "down spread". During center spread modulation, the deviation from the target frequency is equal in the positive and negative directions. The effective average frequency is equal to the target frequency. In applications where the clock is driving a component with a maximum frequency rating, down spread should be applied. In this case, the maximum frequency, including modulation, is the target frequency. The effective average frequency is less than the target frequency. The ICS251 operates in both center spread and down spread modes. For center spread, the frequency can be modulated between +/- 0.125% to +/-2.0%. For down spread, the frequency can be modulated between -0.25% to -4.0%. Both output frequency banks will utilize identical spread spectrum percentage deviations and modulation rates, if a common VCO frequency can be identified.
ICS251 Configuration Capabilities
The architecture of the ICS251 allows the user to easily configure the device to a wide range of output frequencies, for a given input reference frequency. The frequency multiplier PLL provides a high degree of precision. The M/N values (the multiplier/divide values available to generate the target VCO frequency) can be set within the range of M = 1 to 2048 and N = 1 to 1024. The ICS251 also provides separate output divide values, from 2 through 20, to allow the two output clock banks to support widely differing frequency values from the same PLL. Each output frequency can be represented as:
OutputFreq
=
REFFreq ------------------------------------OutputDivide
---M N
Output Drive Control
The ICS251 has two output drive settings. Low drive should be selected when outputs are less than 100 MHz. High drive should be selected when outputs are greater than 100 MHz. (Consult the AC Electrical Characteristics for output rise and
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Spread Spectrum Modulation Rate
The spread spectrum modulation frequency applied to the output clock frequency may occur at a variety of rates. For applications requiring the driving of "down-circuit" PLLs, Zero Delay Buffers, or those adhering to PCI standards, the
spread spectrum modulation rate should be set to 30-33 kHz. For other applications, a 120 kHz modulation option is available.
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS251. These ratings, which are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can affect product reliability. Electrical parameters are guaranteed only over the recommended operating temperature range.
Parameter
Supply Voltage, VDD Inputs Clock Outputs Storage Temperature Soldering Temperature Junction Temperature
Condition
Referenced to GND Referenced to GND Referenced to GND Max 10 seconds
Min.
-0.5 -0.5 -0.5 -65
Typ.
Max.
7 VDD+ 0.5 VDD+ 0.5 150 260 125
Units
V V V C C C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature (ICS251M) Ambient Operating Temperature (ICS251MI) Power Supply Voltage (measured in respect to GND) Power Supply Ramp Time
Min.
0 -40 +3.15
Typ.
Max.
+70 +85
Units
C C V ms
+3.3
+3.45 4
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DC Electrical Characteristics
Unless stated otherwise, VDD = 3.3 V 5%, Ambient Temperature -40 to +85C
Parameter
Operating Voltage
Symbol
VDD
Conditions
Configuration Dependent - See VersaClockTM
Min.
3.15
Typ.
3.3
Max.
3.45
Units
V mA
Operating Supply Current Input High Voltage
IDD
33.3333 MHz output, PDTS = 1, no load Note 1 PDTS = 0 S1:S0 S1:S0 VDD-0.5
14
mA
500 VDD/2+1 0.4 0.4
Input High Voltage Input Low Voltage Input High Voltage, PDTS Input Low Voltage, PDTS Input High Voltage Input Low Voltage Output High Voltage (CMOS High) Output High Voltage Output Low Voltage Short Circuit Current Nominal Output Impedance Internal pull-up resistor Internal pull-down resistor Input Capacitance
VIH VIL VIH VIL VIH VIL VOH VOH VOL IOS ZO RPUP RPD CIN
A V V V V V VDD/2-1 V V V 0.4 V mA k k pF
ICLK ICLK IOH = -4 mA IOH = -8 mA (Low Drive); IOH = -12 mA (High Drive) IOL = 8 mA (Low Drive); IOL = 12 mA (High Drive)
VDD/2+1 VDD-0.4 2.4 VDD-0.4
70 20 S1:S0, PDTS CLK output inputs 190 120 4
Note 1: Example with 25 MHz crystal input with output of 33.3 MHz, no load, and VDD = 3.3 V.
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AC Electrical Characteristics
Unless stated otherwise, VDD = 3.3 V 5%, Ambient Temperature -40 to +85 C
Parameter
Input Frequency Output Frequency Output Rise Time Output Fall Time Duty Cycle Power-up time
Symbol
FIN
Conditions
Fundamental Crystal Input Clock
Min.
5 3 0.314
Typ.
Max. Units
27 150 200 MHz MHz MHz ns ns 60 10 2 % ms ms
tOR tOF
20% to 80%, Note 1 80% to 20%, Note 1 Note 2 PLL lock time from power-up PDTS goes high until stable CLK output, Spread Spectrum Off PDTS goes high until stable CLK output, Spread Spectrum On 40
1 1 49-51 4 .6
4
7
ms
One Sigma Clock Period Jitter Maximum Absolute Jitter Note 1: Measured with 15 pF load. tja
Configuration Dependent Deviation from Mean. Configuration Dependent
50 +200
ps ps
Note 2: Duty Cycle is configuration dependent. Most configurations are minimum 45% and maximum 55%.
Thermal Characteristics
Parameter
Thermal Resistance Junction to Ambient
Symbol
JA JA JA JC
Conditions
Still air 1 m/s air flow 3 m/s air flow
Min.
Typ.
150 140 120 40
Max. Units
C/W C/W C/W C/W
Thermal Resistance Junction to Case
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Marking Diagram
8 5
Marking Diagram (Pb free)
8 5
251PM ###### YYWW
1
8
251PML ###### YYWW
1 4
4
5
8
5
251PMI ###### YYWW
1 4 1
251PMIL ###### YYWW
4
Notes: 1. ###### is the lot number. 2. YYWW is the last two digits of the year and week that the part was assembled. 3. "I" denotes industrial temp. range (if applicable). 4. "L" denotes RoHS compliant package. 5. Bottom marking: country of origin.
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Package Outline and Package Dimensions (8-pin SOIC, 150 Mil. Body)
Package dimensions are kept current with JEDEC Publication No. 95
8
Millimeters Symbol Min Max
Inches Min Max
E INDEX AREA
H
12 D
A A1 B C D E e H h L
1.35 1.75 0.10 0.25 0.33 0.51 0.19 0.25 4.80 5.00 3.80 4.00 1.27 BASIC 5.80 6.20 0.25 0.50 0.40 1.27 0 8
.0532 .0688 .0040 .0098 .013 .020 .0075 .0098 .1890 .1968 .1497 .1574 0.050 BASIC .2284 .2440 .010 .020 .016 .050 0 8
A A1
h x 45 C
-Ce
B SEATING PLANE L
.10 (.004)
C
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Ordering Information
Part / Order Number
ICS251PM ICS251PMI ICS251PMLF ICS251PMILF ICS251M-XX ICS251MI-XX ICS251M-XXLF ICS251MI-XXLF ICS251M-XXT ICS251MI-XXT ICS251M-XXLFT ICS251MI-XXLFT
Marking
See Page 7 Above
Shipping Packaging
Tubes Tubes Tubes Tubes Tubes Tubes Tubes Tubes Tape and Reel Tape and Reel Tape and Reel Tape and Reel
Package
8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC
Temperature
0 to +70 C -40 to +85 C 0 to +70 C -40 to +85 C 0 to +70 C -40 to +85 C 0 to +70 C -40 to +85 C 0 to +70 C -40 to +85 C 0 to +70 C -40 to +85 C
251M-XX 251MIXX 251MXXL 251MIXXL 251M-XX 251MIXX 251MXXL 251MIXXL
Parts that are ordered with a "LF" suffix to the part number are the Pb-Free configuration and are RoHS compliant. The ICS251M-XX, ICS251M-XXLF, ICS251MI-XX, and ICS251MI-XXLF are factory programmed versions of the ICS251PM, ICS251PMLF, ICS251PMI, and ICS251PMILF. A unique "-XX" suffix is assigned by the factory for each custom configuration, and a separate data sheet is kept on file. For more information on custom part numbers programmed at the factory, please contact your local IDT sales and marketing representative. While the information presented herein has been checked for both accuracy and reliability, IDT assumes no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial applications. Any other applications such as those requiring extended temperature range, high reliability, or other extraordinary environmental requirements are not recommended without additional processing by IDT. IDT reserves the right to change any circuitry or specifications without notice. IDT does not authorize or warrant any IDT product for use in life support devices or critical medical instruments. VersaClockTM is a trademark of Integrated Circuit Systems, Inc. All rights reserved.
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Europe
IDT Europe, Limited Prime House Barnett Wood Lane Leatherhead, Surrey United Kingdom KT22 7DE +44 1372 363 339
(c) 2006 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice. IDT and the IDT logo are trademarks of Integrated Device Technology, Inc. Accelerated Thinking is a service mark of Integrated Device Technology, Inc. All other brands, product names and marks are or may be trademarks or registered trademarks used to identify products or services of their respective owners. Printed in USA

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