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ICS4231-03
Low EMI Clock Generator
Features
• • • •
Pin and function compatible to Cypress W42C31-03 Packaged in 8-pin SOIC (Pb free available) Provides a spread spectrum output clock Accepts a clock or crystal input and provides same frequency dithered output
Description
The ICS4231-03 generates a low EMI output clock from a clock or crystal input. The device uses ICS’ proprietary mix of analog and digital Phase Locked Loop (PLL) technology to spread the frequency spectrum of the output, thereby reducing the frequency amplitude peaks by several dB. The ICS4231-03 offers four different center and down spread selections. Refer to the MK1714-01/02 for the widest selection of input frequencies and multipliers. ICS offers a complete line of EMI reducing clock generators. Consult us when you need to remove crystals and oscillators from your board.
• Input clock frequency of 10 to 33 MHz • Peak reduction by 8dB - 14dB typical on 3rd - 19th
odd harmonics
• Spread percentage selections of ±1.875%, ±1.0%,
and -2.0%
• Operating voltage of 5V • Advanced, low-power CMOS process
Block Diagram
VDD
FS1:0 OE# PLL Clock Synthesis and Spread Spectrum Circuitry
CLK
X1/CLKIN X2
Clock Buffer/ Crystal Oscillator
GND
MDS 4231-03 A
1
●
Revision 110404 tel (408) 297-1 201 ● w w w. i c s t . c o m
In te grated Circuit Systems ● 5 25 Race Stree t, San Jose, CA 951 26
ICS4231-03 LOW EMI CLOCK GENERATOR
Pin Assignment
X1/CLKIN X2 GND FS0 1 2 3 4 8 7 6 5 OE# FS1 VDD CLKOUT
Output Enable Function Table
OE# (Pin 8) 0 1 Output Status Running Tri-state
8 pin (150 mil) SOIC
0 = connect to GND 1 = connect directly to VDD Note: OE# pin has an internal pull-down resistor
Frequency Range and Spread Table
FS1 (Pin 7) FS0 (Pin 4) Clock Input Frequency (MHz) 10-20 10-20 20-33 20-33 Crystal Input Frequency (MHz) 10-20 10-20 20-25 20-25 Spread Amount
0 0 1 1
0 1 0 1
±1.875% ±1.0% ±1.875% -2.0%
Note: FS1:0 have internal pull-up resistors
Pin Descriptions
Pin Number Pin Name Pin Type Pin Description
1 2 3 4 5 6 7 8
X1/CLKIN X2 GND FS0 CLKOUT VDD FS1 OE#
Input Output Power Input Output Power Input Input
Crystal or Clock Input. Crystal output. Float for a clock input. Connect to ground. Select pin for input frequency and spread amount. See table above. Internal pull up resistor. Spread spectrum clock output per table above. Connect to 5V. Select pin for input frequency and spread amount. See table above. Internal pull up resistor. Output Enable. Active Low. See table above. Internal pull-down resistor.
MDS 4231-03 A
2
●
Revision 110404 tel (408) 297-1 201 ● w w w. i c s t . c o m
In te grated Circuit Systems ● 5 25 Race Stree t, San Jose, CA 951 26
ICS4231-03 LOW EMI CLOCK GENERATOR
External Components
The ICS4231-03 requires a minimum number of external components for proper operation.
value of these capacitors is given by the following equation:
PCB Layout Recommendations
For optimum device performance and lowest output phase noise, the following guidelines should be observed. 1) The 0.01µF decoupling capacitor should be mounted on 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. 2) To minimize EMI the 33Ω series termination resistor, if needed, should be placed close to the clock output. 3) 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 ICS4231-03. This includes signal traces just underneath the device, or on layers adjacent to the ground plane layer used by the device.
Decoupling Capacitor
A decoupling capacitor of 0.01µF must be connected between VDD and GND on pins 6 and 3, as close to these pins as possible. For optimum device performance, the decoupling capacitor should be mounted on the component side of the PCB. Avoid the use of vias in the decoupling circuit.
Series Termination Resistor
When the PCB trace between the clock output and the load is over 1 inch, series termination should be used. To series terminate a 50Ω trace (a commonly used trace impedance) place a 33Ω resistor in series with the clock line, as close to the clock output pin as possible. The nominal impedance of the clock output is 20Ω.
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS4231-03. 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.
Item
Supply Voltage.