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NCS2564DTBR2G Datasheet(PDF) 11 Page - ON Semiconductor |
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NCS2564DTBR2G Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 15 page NCS2564 http://onsemi.com 11 APPLICATIONS INFORMATION The NCS2564 quad video driver has been optimized for Standard and High Definition video applications covering the requirements of the standards Composite video (CVBS), S−Video, Component Video (480i/525i, 576i/625i, 720p/1080i) and related (RGB). The three SD/HD channels have selectable filters (8 MHz and 34 MHz) for covering either standard definition−like video applications or High Definition video applications. These frequencies are selectable using the pin SD/HD. In the regular mode of operation each channel provides an internal voltage−to−voltage gain of 2 from input to output. This effectively reduces the number of external components required as compared to discrete approached implemented with stand alone op amps. An internal level shifter is employed shifting up the output voltage by adding an offset of 200 mV. This prevents sync pulse clipping and allows DC−coupled output to the 150 W video load. In addition, the NCS2564 integrates a 6th order Butterworth filter for each. This allows rejection of the aliases or unwanted over-sampling effects produced by the video DAC. Similarly for the case of DVD recorders which use an ADC, this anti−aliasing filter (reconstruction filter) will avoid picture quality issue and will aide filtration of parasitic signals caused by EMI interference. Figure 22. AC−Coupled Configuration at the Input and Output 0.1 mF VCC SD/HD 3 2 114 13 12 CVBS_IN GND GND CVBS_OUT 6 7 411 8 9 SD/HD_EN 5 10 TV 220 mF 75 W 75 W 220 mF 220 mF 75 W 75 W 75 W 75 W Rs Y / G Pb / B Pr / R CVBS Y / G Pb / B Pr / R SD/HD EN CVBS EN SD/HD SEL 75 W Cable 75 W Cable 75 W Cable 220 mF 75 W 75 W CVBS 75 W Cable 0.1 mF 10 mF + 5 V CVBS_EN SD/HD IN1 SD/HD IN2 SD/HD IN3 SD/HD OUT1 SD/HD OUT2 SD/HD OUT3 Rs Rs Rs 0.1 mF 0.1 mF 0.1 mF A built−in diode−like clamp is used into the chip for each channel to support the AC−coupled mode of operation. The clamp is active when the input signal goes below 0 V. The built−in clamp and level shifter allow the device to operate in different configuration modes depending on the DAC output signal level and the input common mode voltage of the video driver. When the configuration is DC−Coupled at the Inputs and Outputs the 0.1 mF and 220 mF coupling capacitors are no longer used, and the clamps are in that case inactive; this configuration provides a low cost solution which can be implemented with few external components (Figure 23). The input is AC−coupled when either the input−signal amplitude goes over the range 0 V to 1.4 V or the video source requires such a coupling. In some circumstances it may be necessary to auto−bias signals with the addition of a pullup and pulldown resistors or only pullup resistor (Typical 7.5 M W combined with the internal 800 kW pulldown) making the clamp inactive. The output AC−coupling configuration is advantageous for eliminating DC ground loop with the drawback of making the device more sensitive to video line or field tilt issues in the case of a too low output coupling capacitor. In some cases it may be necessary to increase the nominal 220 mF capacitor value. Shutdown Mode If the enable pins are left open by default the circuit will be enabled. The Enable pin offers a shutdown function, so the NCS2564 can consequently be disabled when not used. The NCS2564’s quiescent current reduces to 42 mA typical during shutdown mode. DC−Coupled Output The outputs of the NCS2564 can be DC−coupled to a 150 W load (Figure 23). This has the advantage of eliminating the AC−coupling capacitors at the output by reducing the number of external components and saving space on the board. This can be a key advantage for some applications with limited space. The problems of field tilt effects on the video signal are also eliminated providing the best video quality with optimal dynamic or peak−to−peak amplitude of the video signal allowing operating thanks to the built−in level shifter without risk of signal clipping. In this coupling configuration the average output voltage is higher than 0 V and the power consumption can be a little higher than with an AC−coupled configuration. |
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