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ISL59111IZ-T7 датащи(PDF) 7 Page - Intersil Corporation |
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ISL59111IZ-T7 датащи(HTML) 7 Page - Intersil Corporation |
7 / 10 page 7 FN6172.4 April 19, 2007 Application Information The ISL59111 is a single supply rail-to-rail output amplifier achieving a -3dB bandwidth of around 8MHz and slew rate of about 40V/µs while demanding only 2mA of supply current. This part is ideally suited for applications with specific micropower consumption and high bandwidth demands. As the performance characteristics above and the features described below, the ISL59111 is designed to be very attractive for portable composite video applications. The ISL59111 features a sync clamp, low pass function, and SAG network at the output facilitating reduction of typically large AC coupling capacitors. See Figure 22. Internal Sync Clamp The typical embedded video DAC operates from a ground referenced single supply. This becomes an issue because the lower level of the sync pulse output may be at a 0V reference level to some positive level. The problem is presenting a 0V input to most single supply driven amplifiers will saturate the output stage of the amplifier resulting in a clipped sync tip and degrading the video image. A larger positive reference may offset the input above its positive range. The ISL59111 features an internal sync clamp and offset function to level shift the entire video signal to the best level before it reaches the input of the amplifier stage. These features are also helpful to avoid saturation of the output stage of the amplifier by setting the signal closer to the best voltage range. The simplified block diagram of the ISL59111 in Figure 22 is divided into four sections. The first, Section A is the Sync Clamp. The AC coupled video sync signal is pulled negative by a current source at the input of the comparator amplifier. When the sync tip goes below the comparator threshold the output comparator is driven negative, The PMOS device turns on clamping sync tip to near ground level. The network triggers on the sync tip of video signal. The Sallen Key Low Pass Filter The Sallen Key is a classic low pass configuration illustrated in Figure 22. This provides a very stable low pass function, and in the case of the ISL59111, a three-pole roll-off at around 8MHz. The three-pole function is accomplished with an RC low pass network placed in series with and before the Sallen Key. One pole provided by the RC network and poles two and three provided by the Sallen Key for a nice three- pole roll-off at around 8MHz. If more aggressive, multiple- pole roll-offs are needed, multiple ISL59111 can be placed in series. There will, of course, be a loss of bandwidth as additional devices are added. AC Output Coupling and the SAG Network Composite video signals carry viable information at frequencies as low as 30Hz up to 5MHz. When a video system output is AC coupled it is critical that the filter represented by the output coupling capacitor and the - + - + IN RIN CIN VDD IN EN GND VDD VDD EN=GND: SHUTDOWN IDD~0 EN=VDD: ACTIVE IDD~1.5mA R1 R2 R3 C1 C3 VDC C2 R6 R5 R4 R7 OUT SAG C5 C4 ROUT RL SYNC CLAMP SALLEN KEY LOW PASS FILTER SAG NETWORK AC COUPLING CAPACITOR 100nF 47µF 22µF 75 Ω 75 Ω FIGURE 22. BLOCK DIAGRAM ISL59111 |
Аналогичный номер детали - ISL59111IZ-T7 |
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Аналогичное описание - ISL59111IZ-T7 |
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