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MAX9512 Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX9512 Datasheet(HTML) 11 Page - Maxim Integrated Products |
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11 / 19 page  Video Filter Amplifier with SmartSleep and Y/C Mixer Circuit _ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ _ 11 Active-Detect Mode The active video detect circuit slices the YIN signal at 4.7% of the power supply (155mV for a 3.3V supply). If the transitions occur at a rate of 14kHz or higher, then a video signal is present. When the MAX9512 detects a video signal with sync at the YIN input, the control logic enters the active-detect mode and enables the load sense circuitry (Figure 3). The supply current is typically 17µA. If an output load is not connected to any amplifier, the MAX9512 remains in active-detect mode. Eight times per second, each load-sense circuit checks for a load by connecting an internal 15kΩ pullup resistor to the output for 1ms. If the output is pulled up, then no load is pre- sent. If the output stays low, a load is connected. Full-Operation Mode If a load is connected to an output, the corresponding filter and amplifier turn on and remain on until the out- put load is disconnected. In full-operation mode, SmartSleep intelligently reduces the supply current based on the input signal presence and output loading. Figures 4 and 5 show which portions of the MAX9512 turn on and which remain off with different load configu- rations. In Figure 4, both filters and the Y/C mixer turn on to generate the composite video signal for the amplifier connected to CVBSOUT1. In Figure 5, only the luma filter turns on, and the Y/C mixer stays off. When an amplifier is on, it continually checks if the load has been disconnected by detecting if the amplifier output is sourcing current during a horizontal line time. If no sourcing current is detected within one horizontal line time (approximately 64µs), the load has been dis- connected and the amplifier returns to active-detect mode. If, at any time, the input video signal is removed, the MAX9512 returns to standby mode. If the SmartSleep feature is not activated and the part is not in shutdown, then the filters and amplifiers com- pletely turn on, regardless of whether there is a video signal at the CVBSIN input and whether there are loads connected at the outputs. CVBS1 CIN YIN COUT YOUT CVBSOUT1 CVBSOUT2 LPF GND +3.3V VDD LOAD SENSE 6dB 75 Ω 75 Ω LPF BUFFER LOAD SENSE BUFFER 6dB LOAD SENSE 6dB 75 Ω LOAD SENSE 6dB 75 Ω MAX9512 17 µA CHROMA LUMA NO LOADS CURRENT DAC CURRENT DAC VIDEO ENCODER VIDEO SIGNAL PRESENT OFF OFF OFF OFF OFF OFF OFF OFF OFF CVBS2 SHDN SMARTSLEEP CONTROL LOGIC ACTIVE VIDEO DETECT +3.3V Figure 3. Active-Detect Mode with No Output Loads |
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Similar Description - MAX9512 |
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