MK3722中文资料

The crystal traces should include pads for small fixed capacitors, one between X1 and ground, and another between X2 and ground. Stuffing of these capacitors on the PCB is optional. The need for these capacitors is determined at system prototype evaluation, and is influenced by the particular crystal used (manufacture and frequency) and by PCB layout. The typical required capacitor value is 1 to 4 pF. To determine the need for and value of the crystal adjustment capacitors, you will need a PC board of your final layout, a frequency counter capable of about 1 ppm resolution and accuracy, two power supplies, and samples of the crystals which you plan to use in production. You will also need measured initial accuracy for each crystal at the specified crystal load capacitance (CL). To determine the value of the crystal capacitors: 1. Connect VDD to 3.3V. Connect pin 5 to the second power supply. Adjust the voltage on pin 5 to 0V. Measure and record the frequency of the CLK output. 2. Adjust the voltage on pin 5 to 3.3V. Measure and record the frequency of the same output. To calculate the centering error:
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MK3722
VCXO PLUS AUDIO CLOCK FOR STB
Description
The MK3722 is a low cost, low jitter, high performance VCXO and PLL clock synthesizer designed to replace expensive discrete VCXOs and multipliers. The patented on-chip Voltage Controlled Crystal Oscillator accepts a 0 to 3.3 V input voltage to cause the output clocks to vary by ±115 ppm. Using ICS’ analog/digital Phase-Locked Loop (PLL) techniques, the device uses an inexpensive 27 MHz pullable crystal input to produce a reference output and a selectable audio clock. ICS manufactures the largest variety of VCXO based timing devices for all applications. Consult ICS to eliminate VCXOs, crystals, and oscillators from your board. The frequency of the on-chip VCXO is adjusted by an external control voltage connected to VIN. Because VIN is a high impedance input, it can be driven directly from an PWM RC integrator circuit.
Series Termination Resistor
When the PCB traces between the clock outputs and the loads are 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.
Pin Descriptions
Pin Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pin Name
X2 X1 VDD VDD VIN GND GND PDTS S2 ACLK GND 27M S0Power Power Input Power Power Power Input Output Power Output Input Power -Input
MK3722 VCXO PLUS AUDIO CLOCK FOR STB
External Component Selection
The MK3722 requires a minimum number of external components for proper operation.
Crystal Tuning Load Capacitors
6 ( f 3.3 ( 3.0 )V – f t arg et ) + ( f 0V – f t arg et ) Error = 10 x --------------------------------------------------------------------------------------- – errorxtal f t arg et
• VCXO tuning voltage of 0 to 3.3 V • Advanced, low power, sub-micron CMOS process
Block Diagram
VDD
3
S2:S0 VIN X1 27 MHz Pullable Crystal
3
PLL/Clock Synthesis Circuitry
Audio Clock Select Table
S2
0 0 0 0 1 1 1 1
S1
0 0 1 1 0 0 1 1
S0
0 1 0 1 0 1 0 1
ACLK (MHz)
8.192 11.2896 12.288 16.9344 18.432 16.384 22.5792 24.576
16 Pin 4.40m m body, 0.65m m pitch TSSO P
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MK3722 VCXO PLUS AUDIO CLOCK FOR STB
Pin Assignment
X2 X1 VD D VD D VIN GND GND PD TS 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 S1 NC VDD S0 27M GND AC LK S2
Decoupling Capacitors
Decoupling capacitors of 0.01µF should be connected between VDD and GND on pins 3 and 4, pins 6 and 7, and pins 11 and 14 as close to the MK3722 as possible. For optimum device performance, the decoupling capacitors should be mounted on the component side of the PCB. Avoid the use of vias in the decoupling circuit.
MDS 3722 B Int egrat ed C ircuit Syste ms
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525 R ace S tr eet, San Jose, CA 95126
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Revision 092502 t el (40 8) 295 -9800
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ACLK
X2
Voltage Controlled Crystal Oscillator
3
27MHz
GND
PDTS
MDS 3722 B In tegr ated C ir cu it S yst ems
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1
5 25 Ra ce Str eet, San Jose, C A 95 126
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Revision 092502 tel ( 408) 2 95-9 800
Features
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