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ICS722
LOW COST 27 MHZ 3.3 VOLT VCXO
Description
The ICS722 is a low cost, low-jitter, high-performance 3.3 volt VCXO designed to replace expensive discrete VCXOs modules. The on-chip Voltage Controlled Crystal Oscillator accepts a 0 to 3.3 V input voltage to cause the output clocks to vary by over ±100 ppm. Using ICS’ patented VCXO techniques, the device uses an inexpensive external pullable crystal in the range of 16.2 to 28 MHz to produce a VCXO output clock at that same frequency. The frequency of the on-chip VCXO is adjusted by an external control voltage input into pin VIN. Because VIN is a high-impedance input, it can be driven directly from an PWM RC integrator circuit. Frequency output increases with VIN voltage input. The usable range of VIN is 0 to 3.3 V. ICS manufactures the largest variety of Set-Top Box and multimedia clock synthesizers for all applications. Consult ICS to eliminate VCXOs, crystals, and oscillators from your board.
Features
• • • • • • • •
Packaged in 8-pin SOIC Operational frequency range of 16.2 MHz to 28 MHz Uses an inexpensive external crystal On-chip patented VCXO with pull range of 230 ppm (minimum) VCXO tuning voltage of 0 to 3.3 V Operating voltage of 3.3 V 12 mA output drive capability at TTL levels Advanced, low-power, sub-micron CMOS process
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Block Diagram
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VDD VIN
X1 16.2-28MHz Pullable Crystal X2
Voltage Controlled Crystal Oscillator
16.2-28MHz Clock (REFOUT)
GND
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MDS 722 A I n t e gra te d C i r c u i t S y s t e m s
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1
525 Race Stre et, San Jo se, CA 9 5126
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Revision 121404 te l (40 8) 2 97-12 01
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w w w. i c st . c o m
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ICS722 LOW COST 27 MHZ 3.3 VOLT VCXO
Pin Assignment
X1 VDD VIN GND 1 2 3 4 8 7 6 5 X2 DC DC REFOUT
ICS722 8-Pin (150 mil) SOIC
Pin Descriptions
Pin Number
1 2 3 4 5 6 7 8
Pin Name
XI VDD VIN GND REFOUT DC DC X2
Pin Type
Input Power Input Power Output — — Input
Pin Description
Crystal connection. Connect to the external pullable crystal. Connect to +3.3 V (0.01µf decoupling capacitor recommended). DataSheet4U.com Voltage input to VCXO. Zero to 3.3 V signal which controls the VCXO frequency. Connect to ground. VCXO CMOS level clock output matches the nominal frequency of the crystal. Do not connect anything to this pin. Do not connect anything to this pin. Crystal connection. Connect to a external pullable crystal.
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MDS 722 A
2
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Revision 121404
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In te grated Circuit Systems
525 Ra ce Street, San Jose, CA 9512 6
tel (4 08) 297-1 201
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ICS722 LOW COST 27 MHZ 3.3 VOLT VCXO
External Component Selection
The ICS722 requires a minimum number of external components for proper operation.
variable load capacitors that “pull” (change) the frequency of the crystal. The crystal specified for use with the ICS722 is designed to have zero frequency error when the total of on-chip + stray capacitance is 14 pF. Recommended Crystal Parameters: Initial Accuracy at 25°C Temperature Stability Aging Load Capacitance Shunt Capacitance, C0 C0/C1 Ratio Equivalent Series Resistance
Decoupling Capacitors
A decoupling capacitor of 0.01µF should be connected between VDD and GND on pins 2 and 4 as close to the ICS722 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.
±20 ppm ±30 ppm ±20 ppm 14 pf 7 pF Max 250 Max 35 Ω Max
The external crystal must be connected as close to the chip as possible and should be on the same side of the PCB as the ICS722. There should be no via’s between the crystal pins and the X1 and X2 device pins. There should be no signal traces underneath or close to the crystal. See application note MAN05.
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Quartz Crystal
Crystal Tuning Load Capacitors
The crystal traces should include pads for small fixed The ICS722 VCXO function consists of the external capacitors, one between X1 and ground, and another crystal and the integrated VCXO oscillator circuit. To DataSheet4U.com between X2 and ground. Stuffing of these capacitors assure the best system performance (frequency pull on the PCB is optional. The need for these capacitors is range) and reliability, a crystal device with the determined at system prototype evaluation, and is recommended parameters (shown below) must be influenced by the particular crystal used (manufacture used, and the layout guidelines discussed in the and frequency) and by PCB layout. The typical required following section shown .