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ML6427CS Datasheet(PDF) 6 Page - Fairchild Semiconductor |
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ML6427CS Datasheet(HTML) 6 Page - Fairchild Semiconductor |
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6 / 17 page  ML6427 6 FUNCTIONAL DESCRIPTION The ML6427 is a quad monolithic continuous time analog video filter designed for reconstructing signals from four video D/A sources. The ML6427 is intended for use in AC coupled input and output applications. The filters approximate a 4th-order Butterworth characteristic with an optimization toward low overshoot and flat group delay. All outputs are capable of driving 2VP-P into AC coupled 150W video loads with up to 35pF of load capacitance at the output pin. They are also capable of driving a 75 W load at 1VP-P. All channels are clamped during sync to establish the appropriate output voltage swing range. Consequently the input coupling capacitors do not behave according to the conventional RC time constant. Clamping for all channels settles within 10ms of a change in video sources. Input coupling capacitors of 0.1µF are recommended for all channels. During sync a feedback error amplifier sources/sinks current to restore the DC level. The net result is that the average input current is zero. Any change in the value of the input coupling capacitors will linearly affect the clamp response times. The RGB channels have no pulldown current sources and are essentially tilt-free. The inputs of the CV channels sink less than 1µA during active video, resulting in a tilt of less than 1mV for 220µF output capacitors. A 1000µF capacitor is recommended for TV applications to minimize tilt in the CV channels. SWAP MULTIPLEXER CONTROL Output pins CVOUT1/YOUTA and CVOUT2/YOUTB are each independently selectable among three input sources (CVINU/Y1, CVINFA/Y2, or CVINFB/Y3) depending on the state of digital inputs SWAP CVF, SWAP CVU, and A/B MUX. This allows the two outputs to remain independent and pass straight through, or to remain independent but swapped, or for both outputs to have the same signal sourcing from either CVINU/Y1, CVINFA/Y2, or CVINFB/Y3 (See Table 1). If SWAP CVF is forced to logic low then CVOUT2/YOUTB is sourced from either the CVINFA/Y2 OR THE CVINFB/Y3 input. If SWAP CVU is logic low then CVOUT1/YOUTA provides video from either the CVINFA/Y2 OR THE CVINFB/Y3 input. If SWAP CVF is logic high then CVOUT2/YOUTB provides video from the CVINU/Y1 input. If SWAP CVU is high then CVOUT1/YOUTA provides video from either the CVINFA/Y2 or the CVINFB/Y3 input. Both SWAP CVF and SWAP CVU will pull low if they are not driven. The ML6427 is robust and stable under all stated load and input conditions. Bypassing both VCC pins directly to ground ensures this performance. Two ML6427s can be connected in a master-slave sync configuration. When using this configuration (See Figure 6) only the “master” ML6427 is required to have a signal with embedded sync present on the CVINFA/Y2 and CVINFB/Y3 inputs. In the absence of sync on the CVINFA/Y2 and CVINFB/Y3 inputs of the “slave” ML6427 it will have its SYNCIN input connected to the SYNCOUT output of the “master” ML6427. SYNCIN AND SYNCOUT PINS Each ML6427 has two sync detectors which control the DC restore functions. The unfiltered channel has its own detector, which controls the DC restore function during the horizontal sync period of the CVINU/Y1 input. The other sync detector controls the DC restore functions for the filtered channels based upon the composite or luma silgnal at the CVINFA/Y2 or CVINFB/Y3 input. Required Setup: A composite or luma or green signal must be present on CVINFA/Y2 or CVINFB/Y3 inputs to provide necessary sync signals to other channels (R, G, B, Y, C). Otherwise, sync must be provided at the SYNCIN pin. For RGB applications the green channel with sync can be used as an input to CVINFA/Y2 or CVINFB/Y3. The SYNCOUT pin provides a logic high when it detects the horizontal sync of either the CVINFA/Y2 or CVINFB/Y3 input (note that one input is selected by the A/B MUX pin). The SYNCIN pin is an input for an external H-sync logic signal to enable or disable the internal DC restore loop for the filtered channels. When SYNCIN is logic high the DC restore function is enabled. For normal operation the SYNCOUT pin is connected to the SYNCIN pin (see Figure 4). If neither the CVINFA/Y2 nor the CVINFB/Y3 has an embedded sync an external sync can be applied on the SYNCIN pin. In master-slave configurations the SYNCOUT of a ML6427 master can be used as the SYNCIN of a ML6427 slave (see Figure 6). VIDEO I/O DESCRIPTION Each input is driven by either a low impedance source or the output of a 75 W terminated line. The input is required to be AC coupled via a 0.1µF coupling capacitor which gives a nominal clamping time of 10ms. All outputs are capable of driving an AC coupled 150 W load at 2VP-P or 1VP-P into a 75W load. At the output pin, up to 35pF of load capacitance can be driven without stability or slew issues. A 220µF AC coupling capacitor is recommended at the output to reduce power consumption. For DC coupled outputs see the Typical Applications section. ANALOG MULTIPLEXER CONTROL The four filter channels each have two input multiplexers which are paired to select between two four-channel video sources ( i.e., composite video plus RGB component video). If A/B MUX is forced to logic high, it will select Bank<A> of the video inputs (CVINFA/Y2, RINA/Y4, GINA/ Y6, BINA/C1) to be enabled. If A/B MUX is logic low then Bank<B> of video inputs (CVINFB/Y3, RINB/Y5,GINB/Y7, BINFB/C2) will be selected. If the A/B MUX is open it will pull to logic high. |
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