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ISL59119IBZ Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL59119IBZ Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 10 page 8 FN6319.1 January 28, 2008 Application Information The ISL59119 is a single-supply rail-to-rail triple (one S-video channel and one composite channel) video amplifier with internal sync tip clamps, a typical -3dB bandwidth of 8MHz and slew rate of about 25V/µs. This part is ideally suited for applications requiring high composite and S-video performance with very low power consumption. As the performance characteristics and features illustrate, the ISL59119 is optimized for portable video applications. Internal Sync Clamp Embedded video DACs typically use ground as their most negative supply. This places the sync tip voltage at a minimum of 0V. Presenting a 0V input to most single supply amplifiers will saturate the output stage of the amplifier resulting in a clipped sync tip and degraded video image. The ISL59119 features an internal sync clamp and offset function that level shifts the entire video signal to the optimum level before it reaches the amplifiers’ input stage. These features also help avoid saturation of the output stage of the amplifier by setting the signal closer to the best voltage range. The simplified block diagram on page 1 shows the basic operation of the ISL59119’s sync clamp. The Y and CVBS inputs’ AC-coupled video sync signal is pulled negative by a current source at the input. When the sync tip goes below the comparator threshold, the comparator output goes high, pulling up on the input through the diode, forcing current into the coupling capacitor until the voltage at the input is again 0V, and the comparator turns off. This forces the sync tip clamp to always be 0V, setting the offset for the entire video signal. The C-Channel is slaved to the Y-Channel and clamped to a 500mV level at the input. Figure 27 shows the setup for testing the clamp’s response to a large step response at the input. Once the signals are clamped at the input they are level shifted by +65mV before being amplified by a gain of x2. The Sallen Key Low Pass Filter The Sallen Key is a classic low pass configuration. This provides a very stable low pass function, and in the case of the ISL59119, a three-pole roll-off at 8MHz. The three-pole function is accomplished with an RC low pass network placed in series with and before the Sallen Key. The first pole is formed by an RC network, with poles two and three generated with a Sallen Key, creating a nice three-pole roll-off at 8MHz. Output Coupling The ISL59119 can be AC or DC coupled to its output. When AC coupling, a 220µF coupling capacitor is recommended to ensure that low frequencies are passed, preventing video “tilt” or “droop” across a line. The ISL59119’s internal sync clamp makes it possible to DC couple the output to a video load, eliminating the need for any AC coupling capacitors, saving board space, cost, and eliminating any “tilt” or offset shift in the output signal. The FIGURE 25. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE FIGURE 26. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE Typical Performance Curves (Continued) JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0 0.4 1.0 0.8 0.2 0.6 0 100 125 150 AMBIENT TEMPERATURE (°C) 50 25 75 85 435mW 909mW θ JA = +23 0°C /W SO T23 -6 JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0 0.2 0.7 0.6 0.1 0.4 0.5 0.3 0 100 125 150 AMBIENT TEMPERATURE (°C) 50 25 75 85 391mW 625mW θ JA = +2 56 °C /W SO T2 3-6 75 Ω 75 Ω 500 Ω 0.1µF NTSC VIDEO 1Hz SQUARE WAVE 150 Ω OUTPUT ISL59119 CH1 CH2 FIGURE 27. DC STEP RESPONSE CIRCUIT ISL59119 |
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