PDF EL4585C Data sheet ( Hoja de datos )

Número de pieza	EL4585C
Descripción	Horizontal Genlock/ 8 FSC
Fabricantes	Elantec Semiconductor
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EL4585C Horizontal Genlock 8 FSC Features 36 MHz general purpose PLL 8 FSC timing (Use the EL4584 for 4 FSC) Compatible with EL4583C Sync Separator VCXO Xtal or LC tank oscillator k2nS jitter (VCXO) User-controlled PLL capture and lock Compatible with NTSC and PAL TV formats 8 pre-programmed popular TV scan rate clock divisors Single 5V low current operation Applications Pixel Clock regeneration Video compression engine (MPEG) clock generator Video Capture or digitization PIP (Picture In Picture) timing generator Text or Graphics overlay timing Ordering Information Part No Temp Range Package Outline EL4585CN b40 C to a85 C 16-Pin DIP MDP0031 EL4585CS b40 C to a85 C 16-Lead SO MDP0027 For 3Fsc and 4Fsc clock frequency operation see EL4584 datasheet Demo Board A demo PCB is available for this product Request ‘‘EL4584 5 Demo Board’’ General Description The EL4585C is a PLL (Phase Lock Loop) sub system designed for video applications but also suitable for general purpose use up to 36 MHz In a video application this device generates a TTL CMOS compatible Pixel Clock (Clk Out) which is a multi- ple of the TV Horizontal scan rate and phase locked to it The reference signal is a horizontal sync signal TTL CMOS format which can be easily derived from an analog composite video signal with the EL4583 Sync Separator An input signal to ‘‘coast’’ is provided for applications where periodic distur- bances are present in the reference video timing such as VTR head switching The Lock detector output indicates correct lock The divider ratio is four ratios for NTSC and four similar ratios for the PAL video timing standards by external selection of three control pins These four ratios have been selected for com- mon video applications including 8 FSC 6 FSC 27 MHz (CCIR 601 format) and square picture elements used in some worksta- tion graphics To generate 4 FSC 3 FSC 13 5 MHz (CCIR 601 format) etc use the EL4584 which does not have the addition- al divide by 2 stage of the EL4585 For applications where these frequencies are inappropriate or for general purpose PLL applications the internal divider can be by passed and an external divider chain used FREQUENCIES and DIVISORS Function 6Fsc CCIR 601 Square Divisor PAL Fosc (MHz) 1702 26 602 1728 27 0 1888 29 5 Divisor NTSC Fosc (MHz) 1364 21 476 1716 27 0 1560 24 546 CCIR 601 divisors yield 1440 pixels in the active portion of each line for NTSC and PAL Square pixels format gives 640 pixels for NTSC and 768 pixels for PAL 6Fsc frequencies do not yield integer divisors Divisor does not include d 2 block 8Fsc 2270 35 468 1820 28 636 Connection Diagram EL4585 SO P-DIP Packages 4585 – 17 Note All information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publication however this data sheet cannot be a ‘‘controlled document’’ Current revisions if any to these specifications are maintained at the factory and are available upon your request We recommend checking the revision level before finalization of your design documentation 4585C 1995 Elantec Inc 1 page Typical Performance Curves Contd Idd vs Fosc EL4585C Horizontal Genlock 8 FSC OSC Gain 20 MHz vs Temp Typical Varactor 4585 – 4 OSC Gain vs Fosc 4585 – 6 Charge Pump Duty Cycle Vs iE 4585 – 7 EL4585 Block Diagram 4585 – 8 4585 – 9 4585 – 1 5 5 Page EL4585C Horizontal Genlock 8 FSC creases Ti decreases For LDET to be low at l llock Ti k 50nS C4 is used mainly to attenuate high frequency noise from the charge pump The effect these components have on time to lock is illustrated below Lock Time Let TeR3C3 As T increases damping increases but so does lock time Decreasing T decreases damping and speeds up loop response but in- creases overshoot and thus increases the number of hunting oscillations before lock Critical damp- ing (ge1) occurs at minimum lock time Because decreased damping also decreases loop stability it is sometimes desirable to design slightly over- damped (gl1) trading lock time for increased stability Typical Loop Filter 4585 – 16 LC Loop Filter Components (Approximate) Frequency (MHz) R2 (kX) R3 (kX) C3 (mF) C4 (mF) 26 602 100 39 0 01 0 001 27 0 100 39 0 01 0 001 29 5 100 43 0 01 0 001 35 468 100 51 0 01 0 001 21 476 100 30 0 01 0 001 24 546 100 36 0 01 0 001 28 636 100 43 0 01 0 001 Xtal Loop Filter Components (Approximate) Frequency (MHz) R2 (kX) R3 (MX) C3 (pF) C4 (pF) 26 602 100 4 3 68 6 8 27 0 100 4 3 68 6 8 29 5 100 4 3 68 6 8 35 468 100 4 3 68 6 8 21 476 100 4 3 68 6 8 24 546 100 4 3 68 6 8 28 636 100 4 3 68 6 8 PCB Layout Considerations It is highly recommended that power and ground planes be used in layout The oscillator and filter sections constitute a feedback loop and thus care must be taken to avoid any feedback signal influ- encing the oscillator except at the control input The entire oscillator filter section should be sur- rounded by copper ground to prevent unwanted influences from nearby signals Use separate paths for analog and digital supplies keeping the analog (oscillator section) as short and free from spurious signals as possible Careful attention must be paid to correct bypassing Keep lead lengths short and place bypass caps as close to the supply pins as possible If laying out a PCB to use discrete components for the VCO section care must be taken to avoid parasitic capacitance at the OSC pins 3 and 5 and FILTER out (pin 7) Remove ground and power plane copper above and below these traces to avoid making a capacitive connection to them It is also recom- mended to enclose the oscillator section within a shielded cage to reduce external influences on the VCO as they tend to be very sensitive to ‘‘hand waving’’ influences the LC variety being more sensitive than crystal controlled oscillators In general the higher the operating frequency the more important these considerations are Self contained VCXO or VCO modules are already mounted in a shielding cage and therefore do not require as much consideration in layout Many crystal manufacturers publish informative litera- ture regarding use and layout of oscillators which should be helpful 11 11 Page

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