Last month, we reported an incident that occurred with an assortment of high-performance equipment having trouble operating up to full potential when using AOC (active optical cable) devices. This month, let’s continue with more discoveries involving power management in HDMI products.

Measuring 18 different branded AOC devices at DPL Labs proved that none of these samples met HDMI power current limits. This is serious and can leave an integrator walking in circles searching for the problem, not only during installation but well after the project is complete.

The interface has power limitations designed specifically for its own operation when working with only passive cable products. There is little left after the system initializes and starts up. It’s designed to generate a 5-volt DC output to be routed to the sink device and deliver a minimum of 50mA (.05 Amps).

This small amount does not leave much energy left to operate other electronic devices on the same bus. But again, it was never intended to be used this way. It is designed for only one purpose and that is to support the HDMI system environment, that’s all.

As we conveyed, when you throw in any active cable devices, more power is required to operate these types of cable products. Now, with so many AOC devices in service, test sampling can be achieved proving that AOC power consumption, in most cases, was causing interoperability issues in the field. 

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These power demands vary from one AOC to another. DPL found that out of 18 AOC products, there were five levels of power consumption measured, all being over HDMI minimums. As an example, there were some AOCs that operated at a reasonable 65mA. For sure, they still breached HDMI limits, but it at least made a good attempt compared with others that had demands of better than 200mA. 

Keep in mind that every source product (AVR, switch, set-top box, etc.) is assigned the job of providing this power to the bus. Remember, under HDMI limits, every source must supply at least 50mA to earn certification.

This also means that any source product can provide more power should companies want to invest in their device’s built-in power supply. This is why a fair amount of devices function when first put into service. But the rules have changed a bit as we’ve entered into full 8K and 10K resolutions. These AOC devices can pull even more power, starving its supply bus and causing failures to occur. 

One such device that was tested reinforced this claim. It was a simple 8K 1×3 switch. Its power output was adequate at 100mA. It had the best 8K and 10K response out of all the other contenders. Then, after 10 minutes of cable testing the device, went dead for no perceptible reason.

Digging in to determine what had occurred, it became evident that one AOC that DPL tested demanded 195mA to function. This high-current demand caused the internal power supply in the switch to overheat and eventually took out the supply. It was not the fault of the switch, but the high current demand of the AOC.

This is something that any integrator should be cautious of — it’s kind of like a delayed fuse reaction that can eventually open and that system you installed a year ago dies.

DPL Labs added cable current testing to its Argumentative Matrix Testing Platform some time ago recognizing these power supply shortfalls. Every AOC tested under the Matrix Test Platform uses the manufacturer’s supplemental external power to alleviate these issues. If you aren’t sure, contact the cable manufacturer directly to help limit your liability. 

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