Electronic Design

Power-Efficient Video Amp Detects Loads

The MAX9516 video amplifier from Maxim Integrated Products doesn’t just detect and report the presence of a video load. It also reduces power consumption when the load isn’t present so system designers can better manage power (see the figure). On top of that, additional features further reduce power consumption in the system.

Designers who use have used traditional video amplifiers have had to add an external circuit or a specialized video connector if they wanted to detect the presence of a video load. Even then, they would only be able detect whether a cable had been connected to the device, not whether there was an actual video load at the other end of the cable. The MAX9516, though, provides built-in load detection and reporting. In addition to providing an external signal via its LOAD pin, in the absence of a load, it automatically places itself in a 31-µW low-power state.

Every 128 ms, the part checks for a load by connecting a 7.5-kO pull-up resistor to the video output for 1 ms. If the video output is pulled up during this test, then no load is present and the LOAD pin remains in the low state. If the video output stays low during the test, then a load is connected and LOAD goes high.

The LOAD state is latched during the sleep time between sense pulses, and load-detect changes are deglitched over a nominal 128-ms period. The status of the video load must remain constant during this deglitch period for LOAD to change state.

The amp consumes just 6 mW quiescent and 12 mW average. It operates from a single 1.8-V supply while retaining the ability to drive a 2-V p-p video signal into a 150-O load, thanks to an internal charge pump that generates the negative supply required for negative-going sync pulses. (On the input side, a transparent input sync-tip clamp allows ac-coupling of input signals with different dc biases.)

The part also offers high input impedance. So if it’s used with a video digital-to-analog converter (DAC), the DAC’s output current can be reduced by a total factor of 16, relative to what would be required when working with conventional video amps.

That’s because the high input impedance means the size of the DAC’s output resistor can be increased from 37.5 to 150 O. Additionally, the video-DAC output current can be reduced by a factor of four, if the system designer takes advantage of the MAX9516’s reduced (0.25 V p-p) full-scale input level.

Beyond that, the MAX9516’s 49-dB (at 100 kHz) power-supply rejection ratio eliminates problems that might arise due to the noise from digital power supplies. Designers can therefore use the system’s digital 1.8-V power supply to power these analog video amps, eliminating the analog supply and saving space and cost.

Priced at $0.55 in lots of 1000 and up, the MAX9516 comes in a 10-pin µDFN package.

Maxim Integrated Products www.maxim-ic.com

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